Technical Field
[0001] The invention relates to a process and products as per the first portion of the independent
claims.
Background Art
[0002] In the art of electrical engineering, by the term "mercury switch" is known an electrical
switch that closes a circuit when a small amount of the liquid metal mercury connects
metal electrodes. The mercury tilt switch represents the most common design of this
control element. It remains in a defined state (open or closed) when tilted one direction
with respect to horizontal and enters the other state when tilted the other direction.
[0004] In recent years, the industry has developed a broad portfolio of tilt switches and
sensors. Owing to the widespread availability of sensor elements based on MEMS technology,
numerous solutions have flooded the market. State-of-the-art tilt sensors measure
inclination at a precision of approximately 0.01 degrees and offer programmable switching
points and various analog and digital interfaces.
[0005] Furthermore, solutions based on liquid or pendulum elements are available, typically
being evaluated inductively, capacitively, or optically. However, these devices as
well are increasingly displaced by MEMS technology.
[0006] US 5751074 A (EDWARD B PRIOR) 05.12.1998 discloses an electrical switch sensitive to an externally
applied inertial and gravitational force, having an enclosure with a closed space;
a conductive fluid filing a first portion of the space and a non- conductive medium
filling a second portion of the space, the conductive fluid and the non-conductive
medium having differing densities; at least two electrodes in communication with the
space; an electrical circuit coupled the contacts and having electrical connections
for connection with a power source and a load, having a semiconductor switching device,
which is responsive to a current through the contacts, a current through the contacts
causing the semiconductor switching device to change in conductivity. An externally
applied force, e.g., gravity or inertial force, causes the conductive fluid to move
within the enclosure with respect to the contacts, altering a current through the
contacts, and thereby changing a conducting state of the semiconductor switching device.
The switch resides within a housing, containing both the enclosure and the electrical
circuit.
[0007] JP H09274842 A (R B CONTROLS KK) 21.10.1997 discloses an earth leakage breaker. An operation test
switch is provided in the earth leakage breaker, and when the switch is manually turned
on, a part of the current bypasses a leakage detecting unit through a resistor, and
the condition the same as the case where a leakage is generated can be artificially
generated. When a leakage is intentionally generated, a relay is electrified, and
a relay contact is turned off. An inclination switch is connected in parallel with
the switch, and when the inclination switch is inclined at the predetermined angle
or more and turned off, the condition that a leakage is generated in the same way
as the condition that the switch is turned off is generated, and a relay contact is
turned off to stop the power supply to an equipment.
[0008] JP 2000146579 A (TOYO DENSO KK) 26.05.2000 discloses a time-constant circuit formed out of capacitors
and a resistor in a detecting circuit and a constant current circuit in the collector
of a controlling transistor. The detecting circuit, formed to output a detected signal
of high level when a Hall detects the rotational condition of a movement beyond a
prescribed angle and comes into a switch-on state, is provided with a time constant
circuit consisting of capacitors and a resistor therein. A constant current circuit
is provided which supplies constant current to the collector of a controlling transistor.
A breakdown diode is provided to serve as a constant current circuit. As a result,
a battery power supply is changed into constant voltage, and collector current which
is consistently constant is fed through the resistor in turning-on the transistor.
Summary of invention
[0009] The invention as claimed is hereinafter disclosed in such a way that the technical
problem with which it deals can be appreciated and the solution can be understood.
Technical Problem
[0010] The described solutions as per the prior art bears two significant downsides compared
to the mercury switch: Due to the use of a sensor element that must be evaluated electronically,
a power supply and at least one switching output are needed which, when procured at
a level of robustness and reliability comparable to that of a mercury switch, are
considerably more expensive. For existing applications requiring a one-to-one replacement
of legacy switches, this often represents a major technical and pricing problem.
Solution to Problem
[0011] The invention proposes a two-wire tilt switch based on electronics which, by design
of a combined supply and output stage, is supplied in both the switch's open and closed
states.
[0012] Preferably, the combined supply and output stage is constructed to produce a small
voltage drop across the switch in its closed state and a low leakage current through
the switch in its open state. This ensures that the switch electronics continues to
be supplied in both switching states.
[0013] In most use cases, these characteristics prove unproblematic, since for applications
such as PLC inputs, switching relays, or simple consumers, such behavior lies well
within the tolerated range. Switching arrangements of this type are known, for example,
in the field of inductive proximity switches and considered customary for both AC
and DC switches.
[0014] As a sensor element, a MEMS acceleration sensor with analog output signal may be
used within the scope of the invention. The currents and voltages required for the
operation and signal evaluation of such MEMS sensor are very low and can thus be supplied
by a combined supply and output stage as outlined above. Further, the switching point
of a tilt switch based on a MEMS sensor may be easily adjusted by suitable analog
or digital signal processing of the sensor output signal.
Advantageous effect of invention
[0015] A switch as per the invention requires only two terminals and may serve to retrofit
any device depending on mercury switches.
Brief description of drawings
[0016]
Figure 1 shows the structural features of the two-wire tilt switch.
Figure 2 illustrates a typical application of the two-wire tilt switch.
Description of embodiments
[0017] The two-wire tilt switch 1 is essentially composed of a combined supply and output
stage 2, a sensor element 3, and an evaluation logic 4.
[0018] The supply and output stage 2 is designed to, in the open state of the switch, exhibit
high resistance between the supply pin 5 and the switching output 6 while still permitting
a low residual current - typically below 1 mA - for internal supply of the sensor
element 7 and evaluation logic 8.
[0019] In the closed state of the switch, the supply and output stage 2 exhibits low resistance
between the supply pin 5 and the switching output 6 while sustaining low residual
voltage - typically about 3 V - to power internal supplies 7 and 8 of the sensor element
3 and evaluation logic 4, respectively.
[0020] In the present embodiment, the sensor element 3 is an analog MEMS sensor with low
current consumption - typically below 500 µA - that provides an analog output signal
9 to the evaluation logic 4. The voltage of the output signal 9 corresponds to the
inclination angle of the MEMS sensor with respect to the horizontal plane.
[0021] The evaluation logic 4 is configured such that it sets or resets, respectively, the
output signal 10 of the evaluation logic 4 depending on the output signal 9 of the
sensor element 3. The evaluation logic 4 is further capable of evaluating and logically
connecting two switching levels. For instance, output signal 10 may be set while output
signal 9 is within a first interval, reset while it is within a second, intermediate
interval, and set again while it is within a third interval. In a preferred embodiment,
such design is employed to implement an axisymmetric switching behavior of the tilt
switch.
[0022] The output signal 10 of the evaluation logic 4 toggles the state of the combined
output and supply stage 2 between the switch's open state (high resistance) and closed
state (low resistance).
[0023] In
Figure 2, the supply pin 5 is connected to a positive supply voltage (traditionally referred
to as "voltage at the common collector", Vcc) while the switching output 6 connects
to an attached load 11. The second terminal of the connected load 11 is connected
to ground (GND) 12.
Industrial applicability
[0024] The invention is applicable, inter alia, throughout the electronics industry.
Reference signs list
[0025] The following reference key lists each reference sign along with the designation
of the feature which it indicates.
- 1
- Two-wire tilt switch
- 2
- Combined supply and output stage
- 3
- Sensor element
- 4
- Evaluation logic
- 5
- Supply pin (Vcc)
- 6
- Switching output
- 7
- Internal supply of sensor element
- 8
- Internal supply of evaluation logic
- 9
- Output signal of sensor element
- 10
- Output signal of evaluation logic
- 11
- Attached load
- 12
- Ground (GND)
Citation list
[0026] The following literature is cited throughout this document.
Patent literature
Non-patent literature
1. A tilt switch (1)
having an open state and a closed state and
comprising an electronics assembly (3, 4),
characterized in
a combined supply and output stage (2) configured such that the assembly (3, 4) is
supplied in both states.
2. Switch (1) as per Claim 1,
characterized in that
the assembly (3, 4) comprises a sensor element (3) and an evaluation logic (4).
3. Switch (1) as per Claim 2,
characterized in that
the supply and output stage (2) has a supply pin (5) and a switching output (6).
4. Switch (1) as per Claim 3,
characterized in that
the supply and output stage (2) is adapted to offer high resistance in the open state
while allowing residual current to pass between the supply pin (5) and the switching
output (6).
5. Switch (1) as per Claim 4,
characterized in that
the residual current amounts to less than 1 mA.
6. Switch (1) as per Claim 3, Claim 4, or Claim 5,
characterized in that
the supply and output stage (2) is adapted to offer low resistance in the closed state
while allowing residual voltage to drop between the supply pin (5) and the switching
output (6).
7. Switch (1) as per Claim 6,
characterized in that
the residual voltage approximates 3 V.
8. Switch (1) as per any of Claim 2 through Claim 7,
characterized in that
the sensor element (3) is microelectromechanical.
9. Switch (1) as per any of Claim 2 through Claim 8,
characterized in that
the sensor element (3) exhibits current consumption below 500 µA.
10. Switch (1) as per any of Claim 2 through Claim 9,
characterized in that
the sensor element (3) is adapted to output an analog signal (9).
11. Switch (1) as per Claim 10,
characterized in that
the analog signal (9) is a voltage signal.
12. Switch (1) as per Claim 10 or Claim 11,
characterized in that
the sensor element (3) is configured such that when the sensor element (3) is supplied
with power, the analog signal (9) of the sensor indicates an inclination angle of
the sensor element (3) with respect to a horizontal plane.
13. Switch (1) as per Claim 10, Claim 11, or Claim 12,
characterized in that
the evaluation logic (4) is adapted to output a digital signal (10) depending on the
analog signal (9).
14. Switch (1) as per Claim 13,
characterized in that
the evaluation logic (4) is configured such that when the sensor element (3) is supplied,
the digital signal (10) is set only if the analog signal (9) falls within a predetermined
range.
15. Switch (1) as per any of the preceding claims,
characterized in that
the combined supply and output stage (2) is adapted to toggle the switch (1) between
the open state and the closed state depending on the digital signal (10).