TWO-WIRE TILT SWITCH

Abstract

 Known tilt switches are less than ideally suited for replacing mercury switches.
Solution
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.

Description

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.

[0003] Since mercury is a poisonous heavy metal, devices containing such switches must be treated as hazardous waste for disposal. In many jurisdictions, mercury is now a restricted substance, and most modern applications have eliminated it. A metal ball and contact wires can directly replace it but may require additional circuitry to eliminate switch bounce. This method of action is further elucidated in FRADEN, Jacob. Handbook of Modern Sensors - Physics, Designs and Applications. 5th edition. Cham Heidelberg New York Dordrecht London: Springer, 2016. ISBN 3319193023.

[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

[0027] 

UXS 5751074 A (EDWARD B PRIOR) 05.12.1998

JP H09274842 A (R B CONTROLS KK) 21.10.1997

JP 2000146579 A (TOYO DENSO KK) 26.05.2000

Non-patent literature

[0028] FRADEN, Jacob. Handbook of Modern Sensors - Physics, Designs and Applications. 5th edition. Cham Heidelberg New York Dordrecht London: Springer, 2016. ISBN 3319193023.

Claims

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).

Drawing