OPERATION VOLTAGE CONTROLLER AND METHOD FOR CONTROLLING AN OPERATION VOLTAGE CONTROLLER

Description

[0001] The present invention relates to an operation voltage controller for a signal powered device having a display and a method for controlling an operation voltage controller of a signal powered device having a display in accordance with claim 1 and claim 12, respectively.

[0002] There are so called signal powered devices. Such devices are operated at locations where it is not desired to have a separate power supply, for instance for safety reasons, because at these locations sparks and heat is to be avoided such as a gas and/or fuel pipe.

[0003] Such devices are normally powered by a loop signal and/or a transmission signal, for instance an analogue 4-20 mA loop signal or a bus signal, like the Fieldbus H1 or the Profibus PA. For example, the loop signal can be an analogue 4-20 mA output signal provided for instance to an electro pneumatic actuator position controller for a pneumatic valve actuator, as SRD991, SRD960 or any competitive device. The loop signal can be an analogue 4-20 mA input signal from, for example, a transmitter device, which converts any physical measured value to a 4-20 mA loop signal. The transmission signal can be a 2-wire bus that provides the communication signal to transfer process variables and other information and the power distribution of the field device at the same time.

[0004] Devices, which are powered by a signal have in most cases a limited power budget and need a special power management to drive their own electronic. In addition energy has to be provided for any special tasks of the device, for instance if the device is an output device for a process control system, which for instance has to drive an electro pneumatic transducer or converter (current or voltage to pneumatic flow or pneumatic pressure), and/or other output actuators and/or to drive in addition sensors e. g. to measure pressure and/or position of the actuator and/or sensors for additional diagnostic measurements. For instance, if the device is an input device for a process control system, the device has to drive in addition to its own basic operating electronic the sensor for the physical input, diagnostic sensors, a local display etc. A bus device can be used as input or output device or both for a process system. In most cases it is necessary, to have on such devices also a local display in addition to the communication, or if communication is not featured or not available, to operate the device by configuring the features, calibrating physical inputs or calibrating actuators to any process needs or it is to read measured values. Because of the lack on power on such signal powered devices, back lightening of the local LCD display has never been provided and/or envisaged by the skilled person.

[0005] As stated the signal powered devices normally do have a display for providing the operator with information needed, for instance for services such as configuration, operation and/or diagnostics services. These displays have never been commercial available with a back light means due to the limited power available for the signal powered devices. For the same reasons self-luminous displays like OLED panels have never been commercial available for such displays. However the back light means and/or an OLED display would be advantageous to have, especially for signal powered devices at dark locations where the display cannot read without having a back light means. It is clear, that external lighting means cannot easily be used for safety reasons.

[0006] US 2007/0161273 A1 discloses a a field unit having a power measuring device determining the power existing in the field unit and a power distribution device for activating and deactivating the display light drive device. This known field unit has the disadvantage that power is needed for the power measuring device and the power distribution device. Therefore the display light drive device may not be activated if there is not enough power in the field unit. Furthermore measuring the power and calculating the available excess power takes some time resulting in a response to changes of the signal power and the power demand of the field device.

[0007] Accordingly it is an object of the present invention to provide a signal powered device having a display with an improved power management being able to provide a back light means and/or a self illuminated display such as an OLED panel.

[0008] This object of the invention is achieved by a signal powered device in accordance with the features of claim 1. Preferred embodiments are disclosed in the dependent claims.

[0009] The object of the invention is also achieved by method in accordance with the features of claim 12. Preferred embodiments are disclosed in the dependent claims.

[0010] An OLED-panel may be used instead of using a LCD display with a backlighting device. OLED-panel need to be provided with a current and are self-luminous. Accordingly OLED-panels do not require a backlighting device. Normally OLED's have three separate matrices, one for each colour. In order to safe energy, it may be preferred to use less colours. It also may be possible to use an OLED-panel with one colour. Alternatively or in addition it may be possible to control less pixel, for instance every second in each direction which will result into a quarter of required energy for driving the OLED-panel. Alternatively or in addition it may be possible to reduce the contrast such that the writing a still readable. Alternatively or in addition it may be possible to increase the contrast as much as possible due to the excess power available. Preferably the contrast should be limited to an upper threshold, at which any further excess energy is to be sunk.

[0011] In accordance with the invention the regulation may be made with an analogous regulation for regulating the operation voltage of the basic device functions means, for instance a transistor.

[0012] The use of an analogous regulation has the advantage that the regulation can be very quick because no measuring and calculating is required. Accordingly the operation voltage for the basic device functions means can be better stabilized. Preferably the regulation does not consider the power the basic device function means required but regulates the stability of the operation voltage (for instance 3 volt). Any excess power will be provided to the back lighting means. If there is more power provided by the signal, a higher current may be provided to the back lighting means. If the power provided to the back lighting means exceeds a predetermined threshold, the power exceeding the threshold will be sunk, for instance by means of a resistor into heat.

[0013] The embodiment of the invention has the advantage that no means for measuring the signal power and the available excess power are needed. The regulation of the operation voltage is sufficient to ensure the proper function of the basic device functions means. Accordingly the regulation means provides a power distribution based on the operation voltage control for the basic device functions means. Therefore any load changes of the basic device functions means and/or changes of the signal power are compensated very quickly and in any case much faster as compared with the prior art field unit having a measuring device and a calculation unit.

[0014] Changes of the power consumption of the basic device functions means may result for instance from digital components like processors, storage means, timers, A/D-converters and D/A-converters, from switching measuring bridges on and off, and from current changes of actuators (Current-pressure-converters, current-pressure-converters), especially if such actions are using only short time peak currents and are set thereafter into a sleeping mode where no current is consumed.

[0015] In accordance with the invention a strategy has been developed, to deal with the low amount of available energy, such that the operation of a back light with some power reserve becomes possible. According to the invention the highest priority is given for applying enough power to the basic device functions for operating the device. The power consumption of the basic device functions varies over time and depends on the operation tasks.

[0016] The system signal, for example the 4-20mA signal, provides more or less power from the system to the signal powered device. If for instance the signal current of a 4-20mA signal is 4mA, and if then the terminal input voltage of the signal powered device is for instance 10V, the power consumed by the device is 40mW. For a 20mA signal current at the same voltage of 10V, the power consumption is 200mW.

[0017] In the worst cases the basic function of the device has to be operable at least at 3.6mA, even if the basic function can have its highest power consumption. The power consumption of the basic functions mostly vary in time cycles of approximately 1ms to Is, especially, if micro controllers are used in the electronic design, which normally have an interrupt controlled software system.

[0018] The power consumption peaks and consumption breaks vary sometimes from 10% to 200% of the minimum input power (36mW). Without an efficient energy buffer the operation above 100% peak power would not be possible, even not for a short time. The energy buffer takes the loop signal power that is more or less not used from the basic function.

[0019] When the buffer is full the unused power must be eliminated. The usual way is to sink the current into a zener diode or to sink the current with a transistor or any variable resistor element. In accordance with the invention most of this energy, which would be otherwise sunk, is stored and used to drive a minimum of one back light LED, or some back light LED's in series or parallel with this unused current. With other words, the LED's are used to sink excess energy and also used to provide back light illumination for the display of the signal powered device.

[0020] Every load variation of the basic function leads to a variation of back light current. The fast load variation cycles are normally not recognized from the user eyes, when he is viewing the LCD display graphics. Therefore the operator will not recognize a variation of the back light level but see a constantly back lighted display.

[0021] In accordance with the invention the back light means (for instance LED's) can be operated by the operation voltage as follows: If there are high operation voltage changes due to load changes of the basic device functions, the back light current will sink the excess energy and improves the stability of the operating voltage. Further excess energy can be sunk by directing some current through a load (For instance if maximum energy is provided to the back light means). In accordance with this embodiment changes of the back light current will be smoothed.

[0022] In accordance with the invention the back light means (for instance LED's) can be coupled to the buffer. If the energy buffer is charged sufficiently, the unused current can be directed through the back light means. Further excess energy can be sunk by directing some current through a load (For instance if maximum energy is provided to the back light means). In accordance with this embodiment changes of the back light current will be smoothed.

[0023] In accordance with the invention the stability of the power supply can also be achieved by a voltage controller that charges and discharges a buffer. Details of this solution are disclosed for instance in the document EP 1 22 427 A1 having the title "Load Voltage Control for a Field Device".

[0024] The buffer can comprise for instance a capacitor or a gold capacitor with a very high capacitance, as described for instance in EP 1 22 427 A1. In accordance with one embodiment the back light means (for instance the LED's) can be switched on whenever the operating power as used by the signal powered device is less than available input power from the signal and/or the energy buffer can provide sufficient energy.

[0025] Preferably, a threshold can be provided for the operation of the back light means, such that the back light means will be switched on only if sufficient excess energy is available from the signal and/or the buffer.

[0026] In accordance with the invention the buffer can comprise an accumulator. Depending on the exact design, the charge time and discharge time of the buffer can be increased.

[0027] Preferably, a threshold can be provided for the operation of the back light means, such that the back light means will be switched on only if sufficient excess energy is available from the signal and/or the buffer.

[0028] In accordance with the invention the buffer can comprise in addition a battery. One advantage of providing a battery is that power for the back light means will be available from the very beginning of operation. One disadvantage is that the battery has to be exchanged from time to time, if this advantage is needed anymore.

[0029] To save additional battery or accumulator power for the above mentioned embodiments comprising a buffer with a battery and/or an accumulator, it can be an improvement to switch off the back light means after the operator has used the display and to switch the back light means on again, if the operator starts using the local display of the device (configuration, maintenance, viewing measure values etc.). The switch off function can be provided with a time delay, i.e. the back light means will be switched after a specific time of not operating the device buttons, or can be provided by a menu item. The switch on function can be provided immediately after any button has been pushed by the operator.

[0030] According to the invention the back lighting means can comprise at least one light emitting diode, preferably a plurality of light emitting diodes and more preferred three light emitting diodes.

[0031] According to the invention at least one filter capacitor may be connected in parallel to the at least one light emitting diode or the plurality of light emitting diodes.

[0032] Such embodiments of the invention have the advantage that the backlighting means of the display and/or the self-illuminating display can be operated more stable, for instance without the risk of flaring. Fast changes of the current will result first into charging and discharging of the filter capacitor, before the current at the display will change. Variations of the brightness of the display will be reduced accordingly.

[0033] According to the invention the backlighting means may comprise at least one "true green" LED and preferably three "true green" LED's.

[0034] These embodiments of the invention have the advantage that the operation voltage for backlighting means do not have to be emphasised, because the forward bias of the "true green"-LED is between 2,2 volt to 2,7 volt depending on the current of 0-10 mA. The distribution of the excess current of the operation voltage will be very easy, for instance by means of a transistor as regulation means. If a constant operation voltage is required for the basic device functions means, a current limit for the backlighting means (LED's) can be realised by means of a resistor (I_limit=(U_operation - U_LED)/R. At the current limit the regulation means will respond with a considerable increase of the regulation output, because with a minimal increase of the operation voltage the regulation means attempts to distribute more current to the backlighting means. In accordance with preferred embodiments of the invention a further transistor is provided which will be activated by this increase of the operation voltage in order to sunk further excess power into a resistor to generate heat such that the operation voltage will be stabilized further. For embodiments having a user operated switch for deactivating the backlight means, the excess power can be sunk by such a transistor to resistors after the backlighting means is deactivated.

[0035] In accordance with the invention the communication can be made by: HART, FOXCOM, Profibus PA, Foundation Fieldbus H1, etc..

[0036] In accordance with the invention the following actuators made by used: positioners and binary outputs.

[0037] In accordance with the invention transmitters may be used for the filling level (displacer principle or lift force measurement, and radar, infrared, or ultrasonic based distance measurement) and/or for pressure measurement, measurement of fluid flow, temperature measurement, position measurement and path measurement.

[0038] In accordance with the invention the following field unit indications may be used: Indication of the standard signal (4 to 20 mA) and any process parameters or physical parameters derived therefore and/or indication of communication of process parameters, physical parameters, measurements signals, positioning signals and/or other conditions from transmitters, actuators and other system components.

[0039] In accordance with the invention the following signals may be used: the standard signal (4 to 20mA, bus signals, which simultaneously provide the power for the operation of the field unit, for instance Profibus PA, Foundation Fieldbus H1, Powered Ethernet etc.).

[0040] Explosion-proof means adapting and designing the circuits for a selfsafe operation in explosion exposed environments for a fault-tolerant backup of circuit components, which otherwise would result to an explosion danger due to overheating or sparking. This will be achieved by using voltage limiting elements, which are preferable provided double to be fault proof, and pre-resistors, which limit power and current. To avoid sparking of discharging capacitors the maximum load voltage is to be adapted to their capacity. Below 5 volt capacities of up to 100µF are possible. For higher voltages the components have to be protected by moulding or other means.

[0041] In accordance with the invention the forward bias of the LED's can be adapted to existing operation voltages by means of switch controls, which transform a higher voltage into a lower voltage und thereby transform the current of the higher voltage into a higher current of the lower voltage or the other way round, if the forward bias of the LED is higher than the operation voltage. For these embodiments the losses are not zero. Therefore the voltage difference and the efficiency of the transformer are critical, whether the effort will be justified in the energy balance. The energy loss of the transformer corresponds to the product of voltage difference times current.

[0042] In accordance with the invention the excess energy being not used to drive the back lighting means may be buffered in a capacitor or an accumulator and used later, if needed.

[0043] In accordance with the invention the display may comprise green, white, yellow and/or blue LED's. These LED's have different forward bias and intensities. The higher the forward bias is, the more energy is needed for the same intensity. Because of the high sensitivity of the human eye for the colour green and the high light yield especially for "true green" LED's, these LED's are preferred. Also green, yellow or red LED's are preferred compared to white and blue LED's because their forward bias is less than 3 volt such that the operation voltage stabilisation can be kept simple and efficient. For white and blue LED's the voltage has to be increased for operating the LED's.

[0044] According to the invention the back lighting means comprises a back light current adjusting means for adjusting the back light current depending on the operation voltage applied at the basic device functions means. Preferably the back light current can be decreased if the operation voltage is below a preset level and can be increased if the operation voltage exceeds the preset level.

[0045] According to the invention the operation voltage controller comprises a buffer designed and adapted to be charged by connecting the buffer to the high voltage output and designed and adapted to be discharged by connecting the buffer to the low voltage output, wherein preferably the back lighting means comprises a back light current adjusting means for adjusting the back light current depending on the charge level of the buffer. Preferably the back light current can be decreased if the charge level of the buffer is below a preset level, preferably a high limit of charge, and can be increased, if the charge level of the buffer exceeds the preset level. In addition and/or alternatively the buffer can be charged, if the output voltage exceeds a set point value, and the buffer can be discharged, if the output voltage does not exceed a set point value. In addition and/or alternatively the buffer can comprise a capacitor, an accumulator and/or a battery.

[0046] According to the invention the operation voltage controller can further comprise a test load for sinking excess energy by applying a test load voltage to the test load such that a test load current is flowing through the test load. Preferably the test load current can be increased, if the back light current is at its maximum, and the test load current can be decreased, if the back light current is below its maximum. In addition and/or alternatively the test load current can be increased, if the buffer voltage exceeds a high limit, and the test load current can be decreased, if buffer voltage does not exceed the high limit.

[0047] According to the invention the operation voltage controller can further comprise a power management controller for controlling the charge level of the buffer, the back light current and/or the test load current. Preferably the power management controller can be supplied with energy by the high voltage output and/or the low voltage output.

[0048] According to the invention the back lighting means can comprise a reflector. Preferably the reflector can be designed and adapted for reflecting light emitted from a light source to the display of the signal powered field device and for providing a support for the display such that the display is located in a specific distance above a printed circuit board onto which the light source is mounted.

[0049] This embodiment has the advantage that the reflector serves a double function. Besides guiding the light the mounting of the display onto the printed circuit board in a specific desired distance will be much simplified, as explained in the detailed description of the preferred embodiments in further detail.

[0050] According to the invention there is also provided a signal powered field device comprising an operation voltage controller in accordance with the invention. Preferably the signal powered field device can further comprise an explosion proof and/or flame proof and/or pressure tight housing which preferably can comprise a window for the display. Preferably the operation voltage controller can comprise at least one switch, preferably a push button, mounted on a printed circuit board and the housing can comprise a corresponding number of actuating means for actuating the switches or push buttons through the wall of the housing.

[0051] According to the invention the back lighting can be made by means of at least one light emitting diode, preferably by means of a plurality of light emitting diodes and more preferred by means of three light emitting diodes.

[0052] According to the invention a back light current can be adjusted depending on the operation voltage applied at the basic device functions means. Preferably the back light current can be decreased, if the operation voltage is below a preset level, and increased, if the operation voltage exceeds the preset level.

[0053] According to the invention the operation voltage controller comprises a buffer, wherein the buffer can be charged by connecting the buffer to the high voltage output and discharged by connecting the buffer to the low voltage output, wherein the back lighting means comprises a back light current adjusting means for adjusting the back light current depending on the operation voltage. Preferably the back light current can be decreased, if the operation voltage is below a preset level, which is preferably a high limit of charge, and increased, if the operation voltage exceeds the preset level. In addition and/or alternatively the buffer can be charged, if the low output voltage exceeds a set point value, and the buffer can be discharged, if the low output voltage does not exceed a set point value.

[0054] According to the invention the method can further comprise the step of sinking excess energy by applying a test load voltage to a test load of the operation voltage controller such that a test load current is flowing through the test load. Preferably the test load current can be increased, if the back light current is at its maximum, and the test load current can be decreased, if the back light current is below its maximum. In addition and/or alternatively the test load current can be increased, if the buffer voltage exceeds a high limit, and the test load current can be decreased, if the buffer voltage does not exceed the high limit.

[0055] According to the invention the method can further comprise the step of switching the basic device functions on, if the test load voltage exceeds an operation start limit.

[0056] In accordance with the invention the method can use an operation voltage controller and/or a signal powered field device in accordance with the invention.

[0057] The LEDs, if used for the back light illumination, can be very sensitive, e.g. 1000-5000 mlum/20mA and/or can have a radiation angle of approx. 120° (depending on the design). Preferably the LEDs are located at optimal locations beneath the display, such that the light is equalized over the backside area of the display (for instance an LCD). There may be provided a diffusing film and a polarization filter. The light reflector of the display at the bottom side of the display (for instance the bottom glass of the LCD) needs to be transparent for the back light, normally 10% transparent and 90% reflecting day light. To improve the back light equalization a diffusing film, a polarization filter and/or a light reflector (preferably having a parabolic profile around the LEDs) can be used. The equalization of light intensity is more important than the intensity itself, in order to provide a better display such that smaller pixel graphics on the display can be read by the operator.

[0058] The invention will be explained in further detail with reference to the drawings, wherein the following reference numbers are used:

1

display and printed circuit board assembly

10

printed circuit board

11

push button

12

light emitting device (LED)

20

reflector

21

edge

22

leg

23

end wall

24

side wall

25

ridge wall

26

extension

27

snap fit

28

pin

30

display

100

cycle of method for controlling an operation voltage controller

101

test: buffer beneath low limit of charge?

102

operation: switch basic device functions off (open switch 206)

103

test: low voltage output exceeds a set point value?

104

operation: charge buffer (close switch 204; open switch 205)

105

operation: discharge buffer (close switch 205, open switch 204)

106

test: buffer exceeds high limit of charge?

107

operation: increase test load current

108

operation: decrease test load current

109

test: test load voltage exceeds operation start limit?

110

operation: switch basic device functions on (close switch 206)

111

test: basic device functions on? (or: switch 206 closed?)

112

test: buffer voltage exceeds high limit?

113

operation: increase back light current

114

operation: decrease back light current

115

test: back light current at maximum?

116

operation: increase test load current

117

operation: decrease test load current

120

node

121

node

122

node

123

node

123A

node

124

node

125

node

200

operation voltage controller

201

power supply

202

test load current adjusting means

203

test load

204

switch (for charging buffer 210)

205

switch (for discharging buffer 210)

206

switch (for switching back lighting means and basic device functions means 212)

207

back light current adjusting means

208

resistor (for current distribution)

209

light emitting device (LED, for back lighting display 30)

210

buffer

211

power management controller

212

basic device functions

213

energy consumption means

214

sensors

215

actuators

216

high voltage output

217

low voltage output

218

operation voltage

219

test load voltage

220

charge buffer signal

221

discharge buffer signal

222

basic device functions on/off signal

223

increase or decrease back light current signal

224

increase or decrease test load current signal

230

filter capacitor

308

graphic pixel controller

309

OLED panel (OLED = Organic light emitting diode)

323

step up driver control signal

330

filter capacitor

331

filter capacitor

332

filter resistor

340

step up DC/DC converter

341

shunt controller

351

row control signal

352

column control signal

[0059] Preferred embodiments of the invention are shown in the attached drawings:

Fig. 1

is a schematic side view of a display and printed circuit board assembly in accordance with an embodiment of the invention.

Fig. 2

is a exploded side view of the display and printed circuit board assembly of Fig. 1.

Fig. 3

is a front view of the display and printed circuit board assembly of Fig. 1.

Fig. 4

is a top view of the reflector of the display and printed circuit board assembly of Fig. 1.

Fig. 5

is a bottom view of the reflector of Fig. 4.

Fig. 6

is a cross section view of the reflector of Fig. 4 along lines VI-VI of Fig. 5.

Fig. 7

is a cross section view of the reflector of Fig. 4 along lines VII-VII of Fig. 5.

Fig. 8

is a perspective top side view of the reflector of Fig. 4.

Fig. 9

is a perspective bottom side view of the reflector of Fig. 4.

Fig. 10

is a circuit diagram of an operation voltage controller in accordance with an embodiment of the invention.

Fig. 11

is a flow chart of the operation voltage controller method in accordance with the invention.

Fig. 12

is a circuit diagram of an operation voltage controller in accordance with another embodiment of the invention.

[0060] Figs. 1 to 3 show a display and printed circuit board assembly 1 in accordance with the invention. On a printed circuit board 10 there is a plurality of push buttons 11 and the display 30.

[0061] The display and printed circuit board assembly 1 of this embodiment is adapted such that it can be mounted into a explosion proof housing. Therefore the display 30 is located a specific distance above the printed circuit board 10 such that the display 30 can be located just beneath a window whereas the push buttons 11 can be located beneath a thick walled housing with actuators extending through the wall in a manner known to the skilled person. Accordingly the display 30 has long pins 31 and 32 to be connected in respective holes of the printed circuit board 10. Normally the pins 31 and 32 are fixed to the holes in the printed circuit board 10 by soldering. However, it is clear that any equivalent means of fixing the pins 31, 32 to the printed circuit board 10 can be used.

[0062] Between the display 30 and the printed circuit board 10 there is arranged a diffusing film 40 and a reflector 20 as it can best be seen from Fig. 2. Optionally a polarization film (not shown) can be located between the display and the diffusing film. Other arrangements known to the skilled person are possible.

[0063] The reflector 20 defines the distance of the display 30 from the printed circuit board 10. The reflector 30 has therefore the double function of providing reflecting walls for reflecting light emitted from light emitting diodes (LEDs) 12 to the display 30 and of ensuring than the display 30 is mounted a specific distance above the printed circuit board 10.

[0064] This is advantageous because in the prior art without having a reflector, fitting the display 30 the specific distance above the printed circuit board has been very difficult and time-consuming. Often a tool has been made by the person fitting the display in order to ensure that the display is located the required specific distance above the printed circuit board. This tool was placed between the display and the printed circuit board before fixing the pins to the printed circuit board. This prior art display and printed circuit board assembly has also the disadvantage that the display may unintentionally be dislocated, for instance by mounting the assembly into its housing, because the pins could have been bent such that the display 30 could have been dislocated to one side and closer to the printed circuit board. In that case an operator may not be able to read the display.

[0065] The reflector 20 will be described in more detail in connection with Figs. 4 to 9. The reflector 20 comprises three openings for LED's 12 (see for instance Fig. 1) mounted at the printed circuit board 10.

[0066] There are parabolic walls at each side of each compartment. As it best can seen from Fig. 4 there are two end walls 23 each defining one wall of the respective outermost compartment. The side walls 24 define opposing walls of all compartments. Between two adjacent compartments, there are respective ridges, each having two ridge walls 25 defining respective side walls of these adjacent compartments.

[0067] Any other walls providing a uniform illumination of the display to be back lighted are possible.

[0068] On the top of the reflector 20 there are means for housing the display and the diffusing film to be placed between the reflector and the display 30. This means as illustrated comprise an extension 26 having at its end a snap fit 27, although other structures known to the skilled person may also be suitable for this purpose.

[0069] As it best can seen in Fig. 7 there are two edges 21 having an inwardly protruding protrusion beneath which the display 30 can be located with its edges.

[0070] The reflector 20 also comprises four legs 22 at the bottom. Two of the legs 22 have a pin 28 to be inserted into a respective hole provided in the printed circuit board 10.

[0071] Fig. 10 is a circuit diagram of an operation voltage controller in accordance with a preferred embodiment of the invention which is generally indicated with the reference number 200.

[0072] This operation voltage controller may be used in a signal powered field device getting its operating power from a signal like a 4-20mA loop signal or getting its operating power from a bus signal like the Fieldbus H1 or the Profibus PA, for example. These field devices have in addition a display to be used for configuration, operation and/or diagnostic purposes on site. For such local operations normally at least one push button is available. Without having a push button information like measurement values and messages may be displayed.

[0073] The power supply 201 gets its energy from the loop signal as schematically indicated at the left hand side of the power supply 201 and indicated by Loop In+ and Loop In-.

[0074] The power supply 201 of this embodiment or any other embodiment of the invention can be embodied with a charged pump for dividing an input voltage and multiplying the output current. Such a charged pump is known to the skilled person from the international application published as WO 98/35430. Such a charged pump is able to move the charge from one voltage level to another voltage level and thus increase the output current while decreasing the output voltage. For instance the charged pump can comprise a current conversion circuit having multiple voltage levels with CMOS gates that switch the output capacitors so as to be coupled to the input of another level to move the charge from one voltage level to another voltage level and thus increase the output current while decreasing the output voltage.

[0075] The loop signal can be a 4-20mA output signal for instance of an electro-pneumatic actuator position controller for pneumatic valve actuators, such as SRD 991, SRD 960 (both are available at the owner of the present invention) or any other competitive device. The loop signal can also be a 4-20mA input signal from for instance a transmitter device, which converts any physically measured value to a 4-20mA loop signal. As stated the energy for the power supply 201 can also be obtained from a transmission signal being a two wire bus that provides the communication signal to transfer process variables and other information and the power distributor of the field device at the same time.

[0076] The power management controller 211 gets the high voltage output 216 of the power supply 201 which is for instance, as shown in Fig. 10, 9V. The power supply 201 also provides a low voltage output 217 which is for instance, as shown in Fig. 10, 3V.

[0077] Between the high voltage output 216 and the low voltage output 217 there are two switches 204, 205 and a buffer 210. The switch 204 is for charging the buffer 210 by connecting the buffer 210 with the high voltage output 216. The switch 205 is for discharging the buffer 210 by connecting the buffer 210 with the low voltage output 217.

[0078] For sinking excess energy there is a test load 203, for instance a resistor which will transform the excess energy into heat. The test load 203 is connected to the low voltage output 217 via an adjusting means 202 provided for increasing or decreasing the test load current 202.

[0079] There are means for back lighting a display as shown for instance in Figs. 1 to 3 and a black box generally depicting the basic device functions means 212. The basic device function means 212 is depicted as black box having energy consumption means 213, schematically depicted sensors 214 and schematically depicted actuators 215. The basic device functions means 212 are known to the skilled person and are not described in further detail here.

[0080] The means for back lighting the display comprise a plurality of LEDs 209. In the depicted embodiment the LEDs are connected in parallel to each other, each having a resistor 208 connected in series thereto. In addition there is an adjusting means 207 provided for increasing or decreasing the back light current for all LEDs. The adjusting means 207 is connected in series to the parallel connection of the LEDs 209 and its respective resistors 208.

[0081] The means for back lighting the display and the basic device functions means 212 are connected in parallel to each other. There is a switch 206 for connecting the back lighting means and the basic device functions means 212 to the low voltage output 217. Switch 206 is therefore for switching the basic device functions means 212 on or off. Since there is a single switch 206, it is clear from Fig. 10, that the back lighting means will only be switched on, if the basic device functions means 212 are switched on and vice versa.

[0082] There is a resulting operation voltage 218 providing energy for operating the back lighting means and the basic device functions means 212.

[0083] In addition there is a power management controller 211 for controlling the power provided to the various means of the circuit.

[0084] The power management controller 211 comprises at least two inputs for observing operation parameters. In the embodiment shown, the power management controller 211 comprises two inputs. The operation voltage 218 is connected to one input for measuring the operation voltage 218. The test load voltage 219 is also observed by the power management controller 211 and connected to its other input.

[0085] The power management controller 211 has at least five outputs controlling the power provided to the various means of the circuit.

[0086] There is the charge buffer signal 220 which is used to close switch 204 if the buffer 210 is to be charged. There is also a discharge buffer signal 221 which is used to close switch 205 if the buffer 210 is to be discharged. It is clear that either switch 204 or 205 is closed. In principal it is also possible that both switches 204 and 205 are open. However in the preferred embodiment the two switches 204 and 205 are closed alternatively and can preferably be embodied as one single component (for instance an OR-switch, or the multistate switch as disclosed in EP 1 202 427 A1.

[0087] There is a basic device functions means on/off signal 222 for operating switch 206. If the basic device functions means 212 are to be switched off switch 206 is opened. If the basic device functions means are to be switched on switch 206 is closed. Together with the basic device functions 212, the back lighting means are switched. However as explained below in further detail, the adjusting means may be regulated such that the back light current is zero if the basic device functions means have been off and are to be switched on.

[0088] There is an increase or decrease back light current signal 223 for operating the adjusting means 207 which will increase or decrease the back light current. The increase or decrease back light current signal 223 can be an analogous signal having a value according to which the adjusting means 207 is to be set. The increase or decrease back light current signal 223 can also be digital, i.e. it can be digital "1" for increasing to back light current and "logical" "0" not decreasing to back light current. In that case the adjusting means 207 will be operated to increase or to decrease the back light current by one step per circle.

[0089] There is an increase or decrease test load current signal 224 for operating the adjusting means 202 which will increase or decrease the test load current. The increase or decrease test load current signal 224 can be realized for instance with one of the options as mentioned in the description of the increase or decrease back light current signal 223.

[0090] Fig. 12 is a circuit diagram of an operation voltage controller in accordance with another embodiment of the invention. This embodiment of the invention essentially corresponds to the embodiment of Fig. 10. Accordingly the same reference numbers have been used for designating similar or the same components. For these components and their related features reference is made to the description of the embodiment of Fig. 10. In the following only the differences are described. In the embodiment of Fig. 12 there is a filter capacitor 230 connected in parallel to the parallel connection of the LED's 209 and its respective resistors 208. It is clear that more than one filter capacitor 230 can be used in order to obtain a higher capacity with lower capacity capacitors. Such capacitors are to be connected in parallel to each other. For instance one filter capacitor 230 can be connected in parallel to a respective series connection of a LED 209 and a resistor 208. This embodiment has the advantage, that fast changes of the backlight means current will result first to charge and discharge currents in and from the filter capacitor(s) 230 before the voltage at the LED's and therefore the current through the LED's changes. Accordingly possible changes of the intensity of the backlight means can be dramatically reduced.

[0091] Fig. 11 is a flow chart of a preferred embodiment of the method according to the invention.

[0092] First the operation will be described if the loop power is switched on the first time and/or the device is installed for the first time and/or after maintenance thereof.

[0093] If the loop power is switched on, the circuit starts at node 120. At block 101 the charge level of the buffer is checked. If the charge level of the buffer is beneath a low limit of charge a signal will be provided, for instance by the power management controller 211 of Fig. 10, according to which the basic device functions are to be switched off. At the very beginning or after a failure the basic device functions will be already off. In that case the basic device functions will not be switched off but kept off. Thereafter the flow chart will jump to node 121. If in block 101 the buffer charge level is not beneath the low limit of charge, the operation will directly jump to node 121.

[0094] Next the operation continues with block 103 where the output voltage of the power supply is checked. If the output voltage exceeds its set point value, the buffer will be charged for a specific time in block 104. If the output voltage does not exceed the set point value the buffer will be discharged in block 105 for a specific time, but only if the charge level of the buffer is above the low limit.

[0095] From block 105 the operation will jump to node 122. From block 104 where the buffer is charged, the operation goes to block 106 where the voltage of the buffer will be checked.

[0096] If the buffer voltage does not exceed a high limit, the operation jumps to node 122. Otherwise the operation continues with block 107 where a signal will be provided in order to increase the test load current. Otherwise following node 122 the operation continues with block 108 where a signal is provided to decrease the test load current. It is clear that in blocks 107, 108 the test load current will be increased or decreased, respectively stepwise, i.e. in each cycle of the flow chart one step.

[0097] The height of the step can be predetermined by a fixed parameter. Alternatively the height of the step can be variable in accordance with the current needs such that the test load current is controlled quicker. It will also be possible to switch the test load current completely on or off in each cycle. Furthermore it is clear that the test load current cannot be decreased below zero or increased above a maximum test load current due to the available energy.

[0098] After block 108 the operation jumps to node 123 and further to node 123A. Following block 107 the operation goes to block 109 where the test load voltage will be checked. If the test load voltage does not exceed the operation start limit, the operation jumps to node 123 and further to node 123A. If the test load voltage exceeds the operation start limit the operation goes to block 110 where a signal will be provided to switch the basic device functions on. If the basic device functions are off, the basic device functions will be switched on for the first time. Otherwise they will stay on. Thereafter the operation goes to node 123A. From node 123A the operation goes to block 111 where a test will be made whether the basic device functions are switched on. If the basic device functions are not switched on, the operation goes back to node 120. This cycle will be made as long as the test load voltage does not exceed the operation start limit.

[0099] From the flow chart of Fig. 11 it is clear that the buffer will be charged at the very beginning after the output voltage exceeds the set point value (see block 103). Thereafter the test load current will be increased until the test load current exceeds an operation start limit (see block 109). During increasing the test load current it will be possible that a buffer voltage falls below the high limit and then the buffer will be recharged sometimes.

[0100] In the following the normal operation will be described, i.e. after the basic device functions have been switched on.

[0101] The operation continues with block 112 where the buffer voltage will be checked. If the buffer voltage does not exceed the high limit the operation goes to block 114 where the back light current will be decreased. Thereafter the operation goes to node 124. If in block 112 the buffer voltage does exceed the high limit, the operation continues with block 113 where the back light current will increased.

[0102] Thereafter the operation continues with block 115 where it is checked whether the back light current is at its maximum value. If the back light current is not at its maximum value the operation continues with node 124. Otherwise, i.e. if the back light current is at maximum, the operation continues with block 116 where the test load current will be increased. Thereafter the operation goes to node 125 and jumps back to the beginning on node 120.

[0103] According to the flow chart of Fig. 11 the back light current will be regulated each time the operation runs one cycle (in normal operation). The frequency of one cycle is very fast such the operator will not notice the alteration of the back light current. If the power management controller 211 is embodied with operational amplifiers, the control frequency is about 50 kHz, e.g. 10 - 100 kHz.

[0104] Normally, it will be sufficient that the alternation frequency of the back light current is higher than 50 Hz. In principle the back light current will be kept at maximum as long as a buffer voltage exceeds the high limit. If the buffer voltage does not exceed the high limit the back light current will be decreased unless the buffer voltage exceeds the high limit again. Therefore the back light current will be high at times the buffer voltage exceeds the high limit, i.e. at times where the basic device functions do not need much energy to be operated.

[0105] As stated above with regard to the test load current, it also will be possible to switch the back light current on and off, in order to simplify the embodiment and/or to increase the frequency of the back light current changes. Instead of increasing the frequency, it will also be possible to increase the step heights.

[0106] A higher speed of the power management controller 211 will improve the stability of the operation voltage 218 as long as the phase shifts are small enough.

[0107] Furthermore, at these times the buffer will be charged up to its maximum. If the buffer is fully charged, the test load current will be increased to sink the energy not needed as long as the back light current is at its maximum. On the other hand, if the basic device functions need more energy, the back light current will be decreased after the buffer voltage drops below a high limit. Normally, the buffer charge will not fall below a low limit such that the basic device functions will be switched off. The basic device functions, i.e. sensors and/or actuators (they normally do not need so much energy) must be designed such that they do not sink more average in the average than the loop power can provide in order to avoid that the buffer will be emptied beneath a low limit of charge.

[0108] For embodiments where the actuator needs much energy for a long time it is recommended to increase the buffer size accordingly.

Claims

1. Signal powered field device with
a display (30), and
an operation voltage controller (200) comprising
a power supply (201) for transforming a loop signal and/or transmission signal into a high voltage output (216) and a low voltage output (217),
a basic device functions means (212) being supplied with an operation voltage (218) by the low voltage output (217), and
a back lighting means for back lighting the display (30), the back lighting means being supplied with the operation voltage,
wherein the operation voltage controller (200) further comprises a buffer (210) designed and adapted to be charged by connecting the buffer (210) to the high voltage output (216) by means of a first switch (204) and designed and adapted to be discharged by connecting the buffer (210) to the low voltage output (217) by means of a second switch (205), wherein the back lighting means comprises a back light current adjusting means (207) for adjusting the back light current depending on the operation voltage (218).

2. Signal powered field device according to claim 1, wherein the buffer comprises a capacitor.

3. Signal powered field device according to any of the preceding claims, wherein the back lighting means comprises at least one light emitting diode or a plurality of light emitting diodes or three light emitting diodes.

4. Signal powered field device according to any of the preceding claims, wherein the back light current is decreased, if the operation voltage is below a preset level, and increased, if the operation voltage exceeds the preset level.

5. Signal powered field device according to any of the preceding claims, wherein the buffer will be charged, if the low output voltage exceeds a set point value, and the buffer will be discharged, if the low output voltage does not exceed a set point value.

6. Signal powered field device according to any of the preceding claims, further comprising a test load (203) and a test load current adjusting means (202) for sinking excess energy by applying a test load voltage to the test load such that a test load current is flowing through the test load and the test load current adjusting means,
wherein the test load current is increased, if the back light current is at its maximum, and the test load current is decreased, if the back light current is below its maximum,
wherein the test load current is increased, if the buffer voltage exceeds a high limit, and the test load current is decreased, if buffer voltage does not exceed the high limit.

7. Signal powered field device according to any of the preceding claims, further comprising a power management controller for controlling the charge level of the buffer and the back light current, wherein the power management controller is supplied with energy by the high voltage output.

8. Signal powered field device according to claim 8, wherein the power management controller also controls the test load current.

9. Signal powered field device according to any of the preceding claims, wherein the back lighting means comprises a reflector; wherein the reflector is designed and adapted for reflecting light emitted from a light source of the back lighting means to the display of the signal powered field device and for providing a support for the display such that the display is located in a specific distance above a printed circuit board onto which the light source is mounted.

10. Signal powered field device according to any of the preceding claims, further comprising an explosion proof and/or flame proof and/or pressure tight housing, wherein the housing comprises a window for the display.

11. Signal powered field device according to any of the preceding claims, wherein the operation voltage controller (200) comprises at least one push button (11) mounted on a printed circuit board and the housing comprises a corresponding number of actuating means for actuating the switch or switches through the wall of the housing.

12. Method for controlling a signal powered field device having an operation voltage controller (200) and a display (30), wherein the operation voltage controller (200) comprises at least a basic device functions means (212), the method comprising the following steps:

transforming a loop signal and/or transmission signal into a high voltage output (216) and a low voltage output (217),

supplying the basic device functions means (212) with the low voltage output (217) such that it is applied as an operation voltage (218) at the basic device functions means (212), and

back lighting the display (30) of the signal powered field device with a back lighting means being supplied with the operation voltage (218),

wherein the operation voltage controller (200) further comprises a buffer (210), and the method comprises the further step of charging the buffer (210) by connecting the buffer (210) to the high voltage output (216) by means of a first switch (204) and discharging the buffer (210) by connecting the buffer (210) to the low voltage output (217) by means of a second switch (205), wherein the back lighting means comprises a back light current adjusting means (207) for adjusting the back light current depending on the operation voltage (218).

13. Method according to claim 12, wherein the back light current is decreased, if the operation voltage is below a preset level, and increased, if the operation voltage exceeds the preset level.

14. Method according to claim 12 or claim 13, wherein the buffer (210) is charged, if the low output voltage exceeds a set point value, and the buffer (210) is discharged, if the low output voltage does not exceed a set point value.

15. Method according to any of claims 12 to 14, further comprising the step of sinking excess energy by applying a test load voltage (219) to a test load (203) and a test load current adjusting means (202) of the operation voltage controller (200) such that a test load current is flowing through the test load (203) and the test load current adjusting means (202), wherein the test load current is increased, if the back light current is at its maximum, and the test load current is decreased, if the back light current is below its maximum.

Ansprüche

1. Signalgespeistes Feldgerät mit
einer Anzeige (30) und
einer Betriebsspannungssteuerung (200), umfassend
eine Energieversorgung (201) zum Transformieren eines Schleifensignals und/oder Übertragungssignals in einen Ausgang hoher Spannung (216) und einen Ausgang niedriger Spannung (217),
einer Gerätegrundfunktionseinrichtung (212), die mit einer Betriebsspannung (218) vom Ausgang niedriger Spannung (217)versorgt wird, und
einer Hintergrundbeleuchtungseinrichtung zum Hintergrundbeleuchten der Anzeige (30), wobei die Hintergrundbeleuchtungseinrichtung mit der Betriebsspannung versorgt wird,
wobei die Betriebsspannungssteuerung (200) weiter einen Puffer (210) umfasst, der so ausgelegt und angepasst ist, dass er durch Verbinden des Puffers (210) mit dem Ausgang hoher Spannung (216) mittels eines ersten Schalters (204) geladen wird, und so ausgelegt und angepasst ist, dass er durch Verbinden des Puffers (210) mit dem Ausgang niedriger Spannung (217) mittels eines zweiten Schalters (205) entladen wird, wobei die Hintergrundbeleuchtungseinrichtung eine Hintergrundbeleuchtungsstrom-Einstelleinrichtung (207) zum Einstellen des Hintergrundbeleuchtungsstroms in Abhängigkeit von der Betriebsspannung (218) umfasst.

2. Signalgespeistes Feldgerät nach Anspruch 1, wobei der Puffer einen Kondensator umfasst.

3. Signalgespeistes Feldgerät nach einem der vorhergehenden Ansprüche, wobei die Hintergrundbeleuchtungseinrichtung mindestens eine Leuchtdiode oder mehrere Leuchtdioden oder drei Leuchtdioden umfasst.

4. Signalgespeistes Feldgerät nach einem der vorhergehenden Ansprüche, wobei der Hintergrundbeleuchtungsstrom verringert wird, wenn die Betriebsspannung unter einem vorbestimmten Niveau liegt, und erhöht wird, wenn die Betriebsspannung über dem vorbestimmten Niveau liegt.

5. Signalgespeistes Feldgerät nach einem der vorhergehenden Ansprüche, wobei der Puffer geladen wird, wenn der Ausgang niedriger Spannung einen Sollwert überschreitet, und der Puffer entladen wird, wenn der Ausgang niedriger Spannung einen Sollwert nicht überschreitet.

6. Signalgespeistes Feldgerät nach einem der vorhergehenden Ansprüche, weiter umfassend eine Prüflast (203) und einer Prüflaststrom-Einstelleinrichtung (202) zum Senken von überschüssiger Energie durch Anlegen einer Prüflastspannung an die Prüflast, so dass ein Prüflaststrom durch die Prüflast und die Prüflaststrom-Einstelleinrichtung fließt,
wobei der Prüflaststrom erhöht wird, wenn der Hintergrundbeleuchtungsstrom bei seinem maximalen Wert liegt, und der Prüflaststrom verringert wird, wenn der Hintergrundbeleuchtungsstrom unter seinem maximalen Wert liegt,
wobei der Prüflaststrom erhöht wird, wenn die Pufferspannung eine obere Grenze überschreitet, und der Prüflaststrom verringert wird, wenn die Pufferspannung die obere Grenze nicht überschreitet.

7. Signalgespeistes Feldgerät nach einem der vorhergehenden Ansprüche, weiter umfassend eine Leistungsverbrauchssteuerung zum Steuern des Ladungsniveaus des Puffers und Hintergrundbeleuchtungsstroms, wobei die Leistungsverbrauchssteuerung vom Ausgang hoher Spannung mit Energie versorgt wird.

8. Signalgespeistes Feldgerät nach Anspruch 8, wobei die Leistungsverbrauchssteuerung auch den Prüflaststrom steuert.

9. Signalgespeistes Feldgerät nach einem der vorhergehenden Ansprüche, wobei die Hintergrundbeleuchtungseinrichtung einen Reflektor umfasst; wobei der Reflektor so ausgelegt und angepasst ist, dass er von einer Lichtquelle der Hintergrundbeleuchtungseinrichtung abgestrahltes Licht zur Anzeige des signalgespeisten Feldgeräts reflektiert und eine Halterung für die Anzeige vorsieht, so dass sich die Anzeige in einem bestimmten Abstand über der Leiterplatte befindet, auf der die Lichtquelle angebracht ist.

10. Signalgespeistes Feldgerät nach einem der vorhergehenden Ansprüche, weiter umfassend ein explosionsgeschütztes und/oder nicht entflammbares und/oder druckfestes Gehäuse, wobei das Gehäuse ein Fenster für die Anzeige umfasst.

11. Signalgespeistes Feldgerät nach einem der vorhergehenden Ansprüche, wobei die Betriebsspannungssteuerung (200) mindestens einen Drucktaster (11) umfasst, der auf einer Leiterplatte angebracht ist, und das Gehäuse eine entsprechende Anzahl von Betätigungseinrichtungen zum Betätigen des Schalters oder der Schalter durch die Wand des Gehäuses umfasst.

12. Verfahren zum Steuern eines signalgespeisten Feldgeräts mit einer Betriebsspannungssteuerung (200) und einer Anzeige (30), wobei die Betriebsspannungssteuerung (200) mindestens eine Gerätegrundfunktionseinrichtung (212) umfasst, wobei das Verfahren die folgenden Schritte umfasst:

Transformieren eines Schleifensignals und/oder Übertragungssignals in einen Ausgang hoher Spannung (216) und einen Ausgang niedriger Spannung (217),

Versorgen der Gerätegrundfunktionseinrichtung (212) mit dem Ausgang niedriger Spannung (217), so dass er als Betriebsspannung (218) an die Gerätegrundfunktionseinrichtung (212) angelegt wird, und

Hintergrundbeleuchten der Anzeige (30) des signalgespeisten Feldgeräts mit einer Hintergrundbeleuchtungseinrichtung, die mit der Betriebsspannung (218) versorgt wird,

wobei die Betriebsspannungssteuerung (200) weiter einen Puffer (210) umfasst, und das Verfahren den weiteren Schritt des Ladens des Puffers (210) umfasst, indem der Puffer (210) mit dem Ausgang hoher Spannung (216) mittels eines ersten Schalters (204) verbunden wird, und das Entladen des Puffers (210) umfasst, indem der Puffer (210) mit dem Ausgang niedriger Spannung (217) mittels eines zweiten Schalters (205) verbunden wird, wobei das Hintergrundbeleuchtungsmittel eine Hintergrundbeleuchtungsstrom-Einstelleinrichtung (207) zum Einstellen des Hintergrundbeleuchtungsstroms abhängig von der Betriebsspannung (218) umfasst.

13. Verfahren nach Anspruch 12, wobei der Hintergrundbeleuchtungsstrom verringert wird, wenn die Betriebsspannung unter einem vorbestimmten Niveau liegt, und erhöht wird, wenn die Betriebsspannung das vorbestimmte Niveau überschreitet.

14. Verfahren nach Anspruch 12 oder Anspruch 13, wobei der Puffer (210) geladen wird, wenn der Ausgang niedriger Spannung einen Sollwert überschreitet, und der Puffer (210) entladen wird, wenn der Ausgang niedriger Spannung einen Sollwert nicht überschreitet.

15. Verfahren nach einem der Ansprüche 12 bis 14, weiter umfassend den Schritt des Senkens der überschüssigen Energie durch Anlegen einer Prüflastspannung (219) an eine Prüflast (203) und eine Prüflaststrom-Einstelleinrichtung (202) der Betriebsspannungssteuerung (200), so dass ein Prüflaststrom durch die Prüflast (203) und die Prüflaststrom-Einstelleinrichtung (202) fließt, wobei der Prüflaststrom erhöht wird, wenn der Hintergrundbeleuchtungsstrom bei seinem Maximalwert liegt, und der Prüflaststrom verringert wird, wenn der Hintergrundbeleuchtungsstrom unter seinem Maximalwert liegt.

Revendications

1. Appareil de terrain alimenté par signal, comprenant
un affichage (30), et
un contrôleur de voltage opérationnel (200) comprenant une alimentation de puissance (201) pour transformer un signal en boucle et/ou un signal de transmission en une sortie à haut voltage (216) et une sortie à bas voltage (217),
un moyen fonctionnel pour dispositif de base (212) qui est alimenté avec un voltage opérationnel (218) par la sortie à bas voltage (217), et un moyen de rétroéclairage pour rétroéclairer l'affichage (30), le moyen de rétroéclairage étant alimenté avec le voltage opérationnel,
dans lequel le contrôleur de voltage opérationnel (200) comprend en outre un tampon (210) conçu et adapté pour être chargé en connectant le tampon (210) à la sortie à haut voltage (216) au moyen d'un premier commutateur (204), et conçu et adapté pour être déchargé en connectant le tampon (210) à la sortie à bas voltage (217) au moyen d'un second commutateur (205), dans lequel le moyen de rétroéclairage comprend un moyen d'ajustement de courant de rétroéclairage (207) pour ajuster le courant de rétroéclairage en fonction du voltage opérationnel (218).

2. Appareil de terrain alimenté par signal selon la revendication 1, dans lequel le tampon comprend un condensateur.

3. Appareil de terrain alimenté par signal selon l'une quelconque des revendications précédentes, dans lequel le moyen de rétroéclairage comprend au moins une diode électroluminescente ou une pluralité de diodes électroluminescentes, ou encore trois diodes électroluminescentes.

4. Appareil de terrain alimenté par signal selon l'une quelconque des revendications précédentes, dans lequel le courant de rétroéclairage est diminué si le voltage opérationnel est au-dessous d'un niveau préétabli, et il est augmenté si le voltage opérationnel excède le niveau préétabli.

5. Appareil de terrain alimenté par signal selon l'une quelconque des revendications précédentes, dans lequel le tampon sera chargé si le bas voltage de sortie excède une valeur fixée, et le tampon sera déchargé si le bas voltage de sortie n'excède pas une valeur fixée.

6. Appareil de terrain alimenté par signal selon l'une quelconque des revendications précédentes, comprenant en outre une charge test (203) et un moyen d'ajustement de courant de charge test (202) pour abaisser une énergie en excès en appliquant un voltage de charge test à la charge test de telle façon qu'un courant de charge test s'écoule à travers la charge test et le moyen d'ajustement de courant de charge test,
dans lequel le courant de charge test est augmenté si le courant de rétroéclairage est à son maximum, et le courant de charge test est diminué si le courant de rétroéclairage est au-dessous de son maximum, dans lequel le courant de charge test est augmenté si le voltage tampon excède une limite haute, et le courant de charge test est diminué si le voltage tampon n'excède pas la limite haute.

7. Appareil de terrain alimenté par signal selon l'une quelconque des revendications précédentes, comprenant en outre un contrôleur de gestion de puissance pour commander le niveau de charge du tampon et le courant de rétroéclairage, dans lequel le contrôleur de gestion de puissance est alimenté avec une énergie par la sortie à haut voltage.

8. Appareil de terrain alimenté par signal selon la revendication 8, dans lequel le contrôleur de gestion de puissance commande également le courant de charge test.

9. Appareil de terrain alimenté par signal selon l'une quelconque des revendications précédentes, dans lequel le moyen de rétroéclairage comprend un réflecteur ; dans lequel le réflecteur est conçu et adapté pour réfléchir la lumière émise depuis une source de lumière du moyen de rétroéclairage vers l'affichage de l'appareil de terrain alimenté par signal et pour fournir un support pour l'affichage de telle façon que l'affichage est situé à une distance spécifique au-dessus d'une carte à circuits imprimés sur laquelle est montée la source de lumière.

10. Appareil de terrain alimenté par signal selon l'une quelconque des revendications précédentes, comprenant en outre un boîtier à l'épreuve des explosions et/ou à l'épreuve des flammes et/ou étanche à la pression, dans lequel le boîtier comprend une fenêtre pour l'affichage.

11. Appareil de terrain alimenté par signal selon l'une quelconque des revendications précédentes, dans lequel le contrôleur de voltage opérationnel (200) comprend au moins un bouton-poussoir (11) monté sur une carte à circuits imprimés et le boîtier comprend un nombre correspondant de moyens d'actionnement pour actionner le ou les commutateur(s) à travers la paroi du boîtier.

12. Procédé pour commander un appareil de terrain alimenté par signal ayant un contrôleur de voltage opérationnel (200) et un affichage (30), dans lequel le contrôleur de voltage opérationnel (200) comprend au moins un moyen fonctionnel pour dispositif de base (212),
le procédé comprenant les étapes suivantes consistant à :

transformer un signal en boucle et/ou un signal de transmission en une sortie à haut voltage (216) et une sortie à bas voltage (217),

alimenter le moyen fonctionnel pour dispositif de base (212) avec la sortie à bas voltage (217), de sorte qu'elle est appliquée à titre de voltage opérationnel (218) au moyen fonctionnel pour dispositif de base (212), et

rétroéclairer l'affichage (30) de l'appareil de terrain alimenté par signal avec un moyen de rétroéclairage qui est alimenté avec le voltage opérationnel (218),

dans lequel le contrôleur de voltage opérationnel (200) comprend en outre un tampon (210), et le procédé comprend l'étape supplémentaire consistant à charger le tampon (210) en connectant le tampon (210) à la sortie à haut voltage (216) au moyen d'un premier commutateur (204) et à décharger le tampon (210) en connectant le tampon (210) à la sortie à bas voltage (217) au moyen d'un second commutateur (205), dans lequel le moyen de rétroéclairage comprend un moyen d'ajustement de courant de rétroéclairage (207) pour ajuster le courant de rétroéclairage en fonction du voltage opérationnel (218).

13. Procédé selon la revendication 12, dans lequel le courant de rétroéclairage est diminué si le voltage opérationnel est au-dessous d'un niveau préétabli, et il est augmenté si le voltage opérationnel excède le niveau préétabli.

14. Procédé selon la revendication 12 ou 13, dans lequel le tampon (210) est chargé si le bas voltage en sortie excède une valeur fixée, et le tampon (210) est déchargé si le bas voltage en sortie n'excède pas une valeur fixée.

15. Procédé selon l'une quelconque des revendications 12 à 14, comprenant en outre l'étape consistant à abaisser une énergie en excès en appliquant un voltage de charge test (219) à une charge test (103) et un moyen d'ajustement de courant de charge test (202) du contrôleur de voltage opérationnel (200), de sorte qu'un courant de charge test s'écoule à travers la charge test (103) et le moyen d'ajustement de courant de charge test (202), dans lequel le courant de charge test est augmenté si le courant de rétroéclairage est à son maximum, et le courant de charge test est diminué si le courant de rétroéclairage est au-dessous de son maximum.

Drawing