[0001] This invention relates to electrically operated apparatus for indicating the lapse
of a pre-determined time period. This may be a continuous, uninterrupted period or
it may be the aggregate of a series of discontinuous time periods of equal or unequal
length.
[0002] Apparatus according to the invention may be used for indicating the end or the approach
of the end of the shelf life of material, such as gold bonding wire, which deteriorates
within a relatively short period of its manufacture. It may also be used for indicating
when, for example, electronic equipment which is required to be periodically aligned
or adjusted is due for such attention. Apparatus according to the invention is, however,
especially well adapted for use in connection with the maintenance of equipment in
the quality assurance field.
[0003] The invention provides an electrically operated apparatus for indicating the lapse
of a predetermined time period the apparatus comprising an indicator element which
is changeable from a first state to a second state when an electrical potential difference
greater than a specified value is applied thereto and is automatically revertable
to the first state when the electrical potential difference applied to the element
is equal to or less that the specified value, in combination with a circuit with means
for controlling as a function of time a potential difference, applied to the indicator
element.
[0004] In use a potential difference is applied to the indicator element such that at the
beginning of the time period the potential difference is greater than the specified
value so that the indicator element changes from the first state to the second state
and at the end of the time period the potential difference is less than or equal to
the specified value and the element reverts to the first state to indicate the lapse
of the period.
[0005] Accordingly the present invention provides a method for indicating the lapse of a
predetermined time period comprising applying a potential difference to an indicator
element which is changeable from a first state to a second state when an electrical
potential difference greater than a specified value is applied thereto and is automatically
revertable to the first state when the electrical potential difference applied to
the element is equal to or less that the specified value, the potential difference
being controlled as a function of time.
[0006] Preferably the applied potential difference is provided R
88 by a source of electric current of known capacity by which any be / meant a source
of electric current that will supply a known current at a substantially constant potential
difference for a known time period, at the end of which period or fairly shortly thereafter
the source is discharged or effectively discharged. The source is effectively discharged
when its potential difference has been reduced to a value equal to or lower than the
specified value as defined above of potential difference referred to in the immediately
preceding definition.
[0007] The source of electric current of known current may be any suitable type of electric
cell or battery such as one or more silver oxide cells. These cells have a relatively
constant voltage during discharge and this voltage falls rapidly when the completely
discharged condition is closely approached.
[0008] An indicator element is a device having a high electrical resistance, usually not
less than 500 kilohm, which changes from a first to a second state when there is applied
to it, via, for example, suitable terminals, an electrical potential difference greater
than a specified value and which reverts automatically to the said first state upon
the reduction of the applied potential difference to a value equal to or less than
the specified value.
[0009] The indicator element may be any suitable electrically operated device. Particularly
suitable is an optical shutter comprising or consisting of an electrochromic device
or a sheet of liquid crystal material. In the latter case the material is associated
with an oscillator or has an oscillator secured to or embedded in it. In one of its
states the optical shutter is transparent and in the other opaque.
[0010] Preferably the applied potential difference is controlled as a function of time by
the circuit, in which a current flows, with a means for controlling the magnitude
of the current.
[0011] The means for controlling the magnitude of the current in the circuit may be a bleed
resistor connected in parallel with the indicator device, or a current controlling
circuit suitably incorporated in the circuit of the apparatus according to the invention.
[0012] In a modification of apparatus according to the invention, so as to enable the apparatus
to indicate the lapse of a predetermined time period which is the aggregate of a series
of discontinuous time periods, means are provided for reducing the current to a very
low if not insignificant value at the end of each time period and then re-establishing
it at or effectively at its previous value at the beginning of the next succeeding
time period without, in either case, the potential difference applied to the indicator
element being materially affected.
[0013] When a bleed resistor is provided in parallel with the indicator device as a means
for controlling the magnitude of the current in the circuit, this resistor may simply
be disconnected at the end of each time period and reconnected at the beginning of
the next succeeding time period.
[0014] Apparatus according to this invention may also include a sensor and an associated
latch circuit. This apparatus will indicate either that a predetermined time period
has elapsed or that certain physical conditions have changed to above or below a preset
limit so that for example the apparatus will indicate that equipment which has been
moved requires recalibration before the predetermined time period has elapsed. Weighing
scales used in shops and in trade should be recalibrated after a certain time period
or after the weighing scales have been moved. Apparatus which includes a sensor that
detects movement can be fixed onto a weighing scales so that the indicator element
will show that the weighing scales need recalibration either after the predetemined
time period has elapsed or the scales have been moved.
[0015] The sensor is used to measure or detect a physical condition such as movement, acceleration,
temperature, pressure, humidity, electro-magnetic radiation, magnetic field, electric
field, alpha particles, beta particles, fluid flow or level or the presence of a certain
gas or fluid. When movement is the physical condition to be detected the sensor may
be a mercury tilt switch which is normally either on or off. When the switch changes
from off to on the associated latch circuit will come into operation and the potential
difference applied to the indicator element will decrease or cease so that the indicator
element will revert to its first state. The latch circuit may be a means of shorting
the terminals of the source of electric current in its simplest form.
[0016] If the sensor has a continuous output, for example a thermistor, a comparator is
included in the apparatus. The comparator compares the output of the sensor with a
preset value and when the output of the sensor reaches that value or is above or below
it as appropriate the associated latch circuit becomes operative and the indicator
element will revert to its first state.
[0017] An apparatus as described as above may be used to indicate the end of the shelf life
of a material which deteriorates after a certain period of time. The material may
also deteriorate if it is subjected to for example high humidity or high temperature.
An apparatus comprising a source of electric current connected by a circuit, which
has a means to control the potential difference (a resistor), to an indicator element
with a sensor and associated latch circuit can be used to indicate that a material
has reached the end of its shelf life. If the sensor is a temperature measuring sensor
the apparatus can also indicate that the material should be disposed of if it has
been subjected to a temperature above a set limit. Some chemical products and pharmaceutical
products are examples of materials which have a certain shelf life as long as they
are kept in certain conditions, eg in a refrigerator, but which deteriorate rapidly
if the temperature rises.
[0018] Embodiments of the invention will now be described by way of example with reference
to the accompanying drawings, of which:
figure 1 is a diagrammatic representation of a first embodiment of a device featuring
an optical shutter and the associated electrical circuit,
figure 2 is a discharge characteristic of a cell suitable for use in the circuit of
fig. 1,
figure 3 is a schematic diagram of the embodiment as shown in figure 1,
figure 4 is a schematic diagram of a second embodiment of a device with an optical
shutter, associated electrical circuit, a detector with two states and a latch circuit,
figure 5 is a schematic diagram of the second embodiment of the device with a detector
with a continuous output and a comparator, and
figure 6 is a circuit diagram of the second embodiment as shown in figure 4.
[0019] Referring now to fig. 1, which illustrates apparatus particularly suitable for indicating
when measuring equiment, such as a thermocouple, is due for recalibration, a silver
oxide cell 1 is connected via a switch 2 to the input terminals 3 of a high input
impedance, 30-100 Hz oscillator 4, the output terminals 5 of which are connected to
the input terminals 6 of a sheet 7 of liquid crystal material which acts as an optical
shutter. The input resistance of this optical shutter is at least 500 kilohms. In
parallel with the input terminals 3 of oscillator 4 are a series-connected resistor
9 and switch 10. Finally, on the underside of the optical shutter is a piece of card
8 or other suitable material bearing the legend "RE-CALIBRATE", preferably in fluorescent
ink.
[0020] The apparatus is intended to indicate the lapse of a predetermined time period and
hence that equipment, such as a thermocouple, for example, is due for re-calibration.
In practice, switches 2 and 10 are closed when the equipment is brought into service,
whereupon the cell 1 begins to discharge via the resistor 9 which acts as a bleed
resistor. It is in part discharged through the input circuit of oscillator 4 but here
the current drain is by comparison negligibly small. Oscillator 4 when energised in
this way applies a low frequency (30-100 Hz) oscillating (alternating) voltage to
the optical shutter 7 from its output terminals 5.
[0021] The liquid crystal material of this optical shutter has a 'first state' in which
it is transparent and a 'second state' in which it is opaque (or essentially so).
Upon the closure of switch 2 (assuming cell 1 is not discharged) the liquid crystal
material is converted to its second state and becomes opaque, thus making it impossible
to read the legend RE-CALIBRATE.
[0022] Upon the closure of switch 10 (switch 2 also being closed) the cell 1 discharges
through the bleed resistor 9 and becomes discharged or effectively discharged after
a period which depends upon the value of resistor 9, the type of cell employed and
to a lesser extent the ambient temperature.
[0023] Cell 1 and resistor 9 are so chosen that the period from 'switch-on', corresponding
to the bringing into service of the equipment, to the time when the cell is discharged
or effectively discharged, at which point the liquid crystal material of optical shutter
7 reverts to its first (transparent) state and the legend RE-CALIBRATE is visible
through the material, corresponds to the "calibration period" of the equipment, upon
the expiry of which period the equipment needs to be re-calibrated. The length of
this period will depend upon the nature of the equipment and the use to which it is
put. It is assumed here that the equipment is either used continuously or is subject
to a known and predictable regime of use.
[0024] The cell 1 should have a rapid fall-off in voltage as it approaches exhaustion (that
is, until it is discharged or effectively discharged) and should preferably have a
relatively constant voltage during discharge prior to this. A discharge characteristic
of such a cell is shown in fig. 2.
[0025] A suitable cell is a DURACELL (Registered Trade Mark) cell, type D350, which has
a nominal voltage of 1.5 volts and a nominal capacity of 100 mAh. Its voltage stays
substantially constant until very near the end of its life when it falls rapidly to
zero as indicated in fig. 2. If it is required that the apparatus of figure 1 should
indicate the lapse of, say, 1000 hours, the resistor R would need to have a value
of

kilohms. The period of 1000 hours is, for example, a typical figure for the life of
a platinum/platinum-rhodium thermocouple before re-calibration is required, when the
thermocouple is used continuously at 1000°C.
[0026] If the equipment is subject to discontinuous periods of use, switch 10 should be
closed at the beginning of each period of use and opened at the end of it, this process
being repeated until the cell 1 is discharged or effectively discharged, whereupon
the word RE-CALIBRATE becomes visible through the optical shutter.
[0027] If the equipment is in continuous use, then the switch 10 may, of course, be omitted.
In addition, switch 2 may also be omitted so as to prevent the accidental switching
off of the cell or battery during use. In this case, the cell or battery would simply
be connected into the circuit upon the bringing into service of the equipment with
which the apparatus of fig. 1 is to be used.
[0028] The first embodiment of the apparatus is also shown as a schematic diagram in figure
3. The device comprises a cell 11 which is connected to input terminals of an oscillator
gate 13. The output terminals of the oscillator gate 13 are connected to input terminals
of an optical shutter 14. A resistor 12 is connected in parallel with the oscillator.
[0029] Referring to figure 4, the device comprises a cell 11, a resistor 12, an oscillator
13, an optical shutter 14, a sensor 15 and a latch circuit 16. The sensor 15 is connected
in parallel with the resistor 12 with an output to an input terminal of the oscillator
gate 13 via a latch circuit 16. Suitable sensors have two states, on or off, for example
a mercury tilt switch. Such a sensor will normally be in the off position until the
physical condition which it is measuring, eg movement, causes it to switch to the
on postion. Latch circuit 16 will then come into effect and the potential difference
supplied to optical shutter 14 will decrease causing optical shutter 14 to revert
to its first state.
[0030] Referring to figure 5, the device is similar to the second embodiment and enables
sensors with a continuous output to be used. A comparator 17 is connected between
the sensor and the latch circuit. Comparator 17 enables the output from sensor 15
to be compared with a preset value such that when the physical condition being measured
by sensor 15 results in the output from sensor 15 reaching the preset value latch
circuit 16 will come into effect. Sensor 15 may measure temperature, pressure, humidity,
electro-magnetic radiation, magnetic fields, electric fields, alpha particles, beta
particles, fluid flow or level or it may detect the presence of a particular fluid
or compound.
[0031] A circuit diagram for the second embodiment of the invention is shown in figure 6.
A cell 21 is connected to an oscillator gate 23A, 23B, 23C, 23D, 23E, 23F which is
connected to an optical shutter 24. A resistor 22 is connected across the terminals
of cell 21. A sensor 25A is connected in parallel with resistor 22. A latch circuit
comprises 26A, 26B, 26C and 26D. The values of resistors 25B and 26D are chosen so
that the power consumption of latch circuit 26A, 26B, 26C and 26D and sensor 25A is
minimal.
[0032] Gates 26A and 26B are NOR gates, 1/4 of a quad 2-input device type 4001B. Gates 23A,
23B and 23C are exclusive OR gates, 1/4 of a quad 2-input device type 4070B.
[0033] It is not of course essential for apparatus according to the invention to be arranged
as just described. A type of optical shutter could for example be used which would
be 'open' (transparent) when the equipment is in use and would only close when the
cell is discharged or effectively discharged. In this case, the legend visible when
the shutter is open could be IN SERVICE, or SERVICEABLE or something similar.
[0034] Yet again, apparatus according to the invention can be used in many fields other
than the indication of the expiry of the "calibration period" of equipment. The legend
displayed could be, for example, RE-ALIGN, SHELF-LIFE ENDED, REPLACE and so on.
[0035] Still further, the indicator element may be one which is not an optical shutter but
which has two messages imprinted on it. One message would be visible in the absence
of an applied potential difference whilst the other message would become visible upon
the application of a potential difference (a.c. or d.c.). The second message could
add to or replace the first message.
[0036] In general, apparatus according to the invention is particularly useful in the quality
assurance field and where any equipment requires periodic attention. It would also
be of considerable value in connection with equipment for the armed forces which requires
periodic checking and in connection with precision laboratory equipment.
[0037] A particular advantage of apparatus according to the invention is that it is fail
safe in that failure of the cell or the battery will have the same effect as its being
discharged or effectively discharged at the end of the period being measured. In other
words, if the cell or battery fails, the apparatus will (prematurely) read RE-CALIBRATE
or RE-ALIGN and so on.
1. An electrically operated apparatus for indicating the lapse of a predetermined
time period, the apparatus comprising an indicator element which is changeable from
a first state to a second state when an electrical potential difference greater than
a specified value is applied thereto and is automatically revertable to the first
state when the electrical potential difference applied to the element is equal to
or less that the specified value, in combination with a circuit with means for controlling
as a function of time a potential difference, applied to the indicator element.
2. An apparatus according to claim 1 wherein a current flows in the circuit and the
applied potential difference is controlled as a function of time by means for controlling
the magnitude of the current.
3. An apparatus according to claim 2 wherein the means for controlling the magnitude
of the current is a bleed resistor.
4. An apparatus according to any preceding claim wherein the indicator element is
an optical shutter.
5. An apparatus according to claim 4 wherein the optical
6. An apparatus according to claim 4 wherein the optical shutter is a sheet of liquid
crystal material.
7. An apparatus according to any preceding claim wherein the circuit further includes
a sensor for sensing a physical condition and a latch circuit, such that the latch
circuit is operable by the sensor to decrease the potential difference and cause the
indicator element to revert to the first state before the end of the predetermined
period of time.
8. An apparatus according to any preceding claim wherein the potential difference
applied to the indicator element is provided by a source of electric current of known
capacity.
9. An apparatus according to claim 7 wherein the source of electric current of known
capacity is at least one electric cell.
10. An apparatus according to claim 8 wherein the cell is a silver oxide cell.
11. A method for indicating the lapse of a predetermined time period comprising applying
a potential difference to an indicator element which is changeable from a first state
to a second state when an electrical potential difference greater than a specified
value is applied thereto and is automatically revertable to the first state when the
electrical potential difference applied to the element is equal to or less that the
specified value, the potential difference being controlled as a function of time.
Dear Sirs, Re: New European Patent Application Johnson Matthey Public Limited Company.
The application was filed on 23rd July 1985 and we regret that we have noticed an
error on page 4 line 13 where "is" should read "may be". Given the priority year has
not yet expired we enclose an amended page 4 in triplicate for insertion into the
specification as filed. Yours Respectfully,