GB2539954A

GB2539954A - A test apparatus

Info

Publication number: GB2539954A
Application number: GB1511666.8A
Authority: GB
Inventors: Richardson Steven
Original assignee: RAMTECH ELECTRONICS Ltd
Current assignee: RAMTECH ELECTRONICS Ltd
Priority date: 2015-07-03
Filing date: 2015-07-03
Publication date: 2017-01-04
Also published as: GB201511666D0

Abstract

A test apparatus 1 for triggering a heat sensitive sensor 2 uses a wire resistor 3 as a heat source. It may be used to ensure that sensor products are in working order prior to either distribution or mounting in final devices. The resistor may be a wound wire resistor and may be configured to emit photons in the infrared range. The apparatus may comprise a comparator 5 adapted to compare an operational parameter of the sensor, such as the current or the resistance, to a predetermined range. It may further comprise a controller 6 adapted to control the flow of current through the resistor, and this flow may be supplied in discrete pulses. The apparatus may also comprise a housing 7 to receive the wire resistor, and a recessed portion 8 adapted to receive the sensor.

Description

A TEST APPARATUS

This invention relates to a test apparatus. More specifically the invention relates to a test apparatus for testing heat sensitive sensors by using a wire resistor as an infra-red (IR) radiation source. It also relates to a method of testing a heat sensitive sensor using a test apparatus.

Pyroelectric sensors detect variations in temperature by measuring a flux of infra-red radiation on a sensing surface of the sensor. Such components are useful in a range of applications Including; fire and flame detection; gas analysis for industrial and medical applications; non-contact temperature measurement; spectroscopy and explosion detection to name a few. A common use of pyroelectric sensors is in motion sensitive passive infra-red detectors (PIR) which are commonly used in homes and businesses as security devices.

It Is vital to ensure that sensor products are in working order prior to either distribution to consumers or mounting the sensors in final devices. In order to perform the testing of heat sensitive sensors, an appropriate source must be chosen.

It is known to test a pyroelectric sensor by exposing the sensor to IR radiation from a source such as a black body radiator with a moving mechanical chopper or a commercial IR source such as the IRS EMIRS200 available from Axetris. Disadvantageously, the use of such sources for testing pyroelectric sensors can be expensive and they may be difficult to control at the low powers required for production testing.

According to a first aspect of the present invention there is provided a test apparatus for triggering a heat sensitive sensor, comprising a wire resistor.

An advantage of the invention as claimed is that the wire resistor may be configured to emit photons substantially in the infra-red range when a current is passed through it. The photons emitted by the wire resistor may trigger the heat sensitive sensor. A wire resistor used as an infra-red source may be cheaper than commercially designed sources, such as the IRS EMIRS200, or black body radiators. A wire resistor may also be easier to control at a range of powers and have long lifetimes.

The wire resistor may be a wound wire resistor. This may be advantageous as it may increase the maximum intensity of photons which can be emitted from the wire resistor per unit length of the wire resistor. The wire resistor may be a bare wire resistor. Alternatively, the wire resistor may be encased by a material which is substantially transparent to at least the desired range of infra-red wavelengths. This may be advantageous as it may serve to physically protect the wire resistor while not greatly inhibiting the transmission of the photons to the heat sensitive sensor.

The test apparatus may comprise a comparator adapted to compare an operational parameter of the heat sensitive sensor to a predetermined range of the operational parameter. The test apparatus may be configured to indicate that the operational parameter is outside of the predetermined range. The test apparatus may be configured to indicate that the operational parameter is within the predetermined range. The operational parameter may be the potential difference across the heat sensitive sensor, for example. This may be advantageous, as both large and small variations in the potential difference across the heat sensitive sensor may be particularly easy to measure.

The controller may set a sensing period during which current is provided to the wire resistor. The controller may inform the comparator when a sensing period is active. The test apparatus may be configured to indicate if the signal from the sensor is not outside of the predetermined range, i.e. a signal event has not been recorded, during the sensing period. This would inform a user if the sensor is not responding as expected.

The predetermined range may be calculated by obtaining a standard response profile for a working pyroelectric detector, calculating an average signal response and setting a threshold level. The predetermined range may be the range of values below the threshold level. Measurements which are above the threshold value may be considered as signal events. Measurements which are below the threshold may be considered as background signals.

The test apparatus may comprise a controller adapted to control the flow of current through the wire resistor. Photons may be emitted from the wire resistor as a result of passing a current through the wire resistor. The controller may be adapted to vary the current flowing through the wire resistor to thereby vary the intensity of emitted infra-red photons. This may be advantageous as a greater or lesser intensity of photons may simulate objects either closer or further from the detector, respectively.

The controller may be adapted to provide current to the wire resistor in a discrete pulse and/or in a plurality of discrete pulses. Each pulse may have an on duration wherein the on duration is the period over which current is supplied to the wire resistor. Between the discrete pulses there may be an off duration wherein the off duration is the period over which current is not supplied to the wire resistor. Typically, when a pyroelectric sensor is used in a PIR apparatus, a Fresnel lens is placed in front of the sensor. A Fresnel lens comprises a plurality of lens sections which focus light onto the sensor while filling a smaller volume than a typical lens, allowing smaller devices to be produced. Providing the current in pulses may be advantageous as it may simulate a response which would be observed by a sensor in typical use in a PIR. A plurality of pulses may be used in order to simulate a plurality of zone breaks on a Fresnel lens. The on duration and the off duration of the current pulses may be varied in order to simulate objects travelling at a range of speeds. The choice of the on duration and the off duration of the current pulses may be, at least in part, based on the bandwidth of the sensor. The on duration of each pulse may be between 0.5 - 2 seconds. The off duration of each pulse may be between 0.5 - 2 seconds.

The comparator and the controller may be the same device. This may advantageously reduce the number of components required in the apparatus.

The test apparatus may further comprise a housing adapted to receive the wire resistor. The controiier may be disposed within the housing. The housing may act as an isolator, substantially isolating the heat sensitive sensor from ambient sources of infra-red radiation. The housing may comprise a recessed portion adapted to receive the heat sensitive sensor. The recessed portion act as the isolator. The recessed portion may have a base and a wall portion. The wire resistor may be disposed within the recessed portion, for example on the base of the recessed portion. The heat sensitive sensor may have a sensing surface which is adapted to face the wire resistor. This may be particularly advantageous as the sensing surface of the heat sensitive sensor may be substantially protected from ambient sources of IR radiation while being in close proximity to the wire resistor.

The test apparatus may be configured to test a piuraiity of sensors consecutiveiy by successiveiy replacing a tested sensor with an untested sensor. The housing may comprise a iocator for iocating the heat sensitive sensor at a predetermined position. An advantage of such a iocator is that the distance between the sensor and the wire resistor may be repeatable, allowing successive tests to be directly comparable. The predetermined position may be defined as a distance between the heat sensitive sensor and the wire resistor. The predetermined distance may be between 2 and 8 mm and optionally between 4.5 and 5.5 mm. The locator may comprise a support member connectable to the housing. The support member may be a printed circuit board which may be advantageous, as additional circuitry required to test the heat sensitive sensor may be mounted on the printed circuit board.

The housing may comprise a connector pin or a plurality of connector pins. The connector pin may be electrically conductive. The controller and/or the comparator may be in electrically conductive connection with the heat sensitive sensor. The engagement of the support member with the connector pin may result in the heat sensitive sensor being located at the predetermined distance from the wire resistor.

The heat sensitive sensor may be a pyroelectric sensor.

In a second aspect of the disclosure there is provided a method for testing a heat sensitive sensor comprising: supplying a current to a wire resistor in proximity to a heat sensitive sensor; measuring an operational parameter of the heat sensitive sensor; and determining if the operational parameter is outside of a predetermined range.

The step of supplying a current may be preceded by controlling the controller to supply a current. The method may comprise the step of exposing the heat sensitive sensor to infrared photons after the step of supplying a current to the wire resistor. The method may comprise the step of locating the wire resistor on the housing. The method may comprise the step of substantially isolating the heat sensitive senor from ambient sources of infrared radiation. The step of isolating the heat sensitive sensor may be accomplished by locating the heat sensitive sensor in a recessed portion of the housing. The method may comprise the step of locating the heat sensitive sensor at a predetermined distance from the wire resistor. The step of supplying a current to the wire resistor comprises supplying a current to the wire a plurality of discrete times such that pulses of infra-red radiation are emitted by the wire resistor. The method may comprise the step of indicating that the operational parameter is outside of the predetermined range.

One or more embodiments will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 shows a test apparatus according to an embodiment of the invention having a heat sensitive sensor received within the recess thereof; and

Figure 2 illustrates a method according an embodiment of the invention fortesting the heat sensitive sensor of Figure 1.

Figure 1 shows a cross section through a test apparatus 1 for triggering a heat sensitive sensor 2 comprising a wire resistor 3. In this example, the heat sensitive sensor 2 is a pyroelectric sensor 2 having a sensing surface 4, however it will be appreciated that other forms of heat sensitive sensor may be triggered by the test apparatus 1, such as thermoelectric sensors. The wire resistor 3 acts as a source of infra-red photons which trigger the pyroeiectric sensor 2 when the photons are incident on the sensing surface 4 of the pyroelectric sensor 2. The pyroelectric sensor 2 is triggered by having infra-red photons incident thereon at which point a change in the potential difference across the sensor 2 is induced. The change in the potentiai difference can be read in order to give an indication or a measure of the change in infra-red emitting sources in the vicinity of the sensor 2.

In this example the wire resistor 3 is a wound wire resistor however it will be appreciated that the resistor 3 may be a straight wire resistor or have another configuration so long as it is able to act as a source of infra-red photons for the pyroeiectric sensor 2. It will also be appreciated that the wire resistor 3 may be bare, i.e. not encased in a protective casing, or it may be enclosed in a protective casing which is substantially transparent to infra-red radiation of a desirable energy or wavelength. The wire resistor 3 provides a cheaper alternative to the infra-red sources used previously and has a long lifetime.

The test apparatus 1 comprises a comparator 5 which is adapted to compare an operational parameter of the heat sensitive sensor 2 to a predetermined range. In this example, the operational parameter to be measured is the potential difference across the sensor 2, however it will be appreciated that a range of operational parameters may provide an indication of photons being incident on the sensor 2, such as the current or the resistance over the sensor 2. The predetermined range can be calculated by obtaining a standard response profile for a working pyroelectric detector, calculating an average signal response and setting a threshold level. The predetermined range will be the range of values below the threshold level. Only measurements which are above the threshold value will be considered as signal events. Measurements which are below the threshold may be considered as background signals. It will be appreciated that alternative ranges may be chosen depending on what may be most advantageous for the sensor 2 being tested, the wire resistor 3 and the comparator 5 being used. The test apparatus 1 is configured to indicate when the potential difference is outside of the predetermined range. In another embodiment, there is provided a sensing period during which current is provided to the wire resistor 3. in this embodiment the controiier 6 may inform the comparator 5 when a sensing period is active. An indication may be provided if the signai from the sensor 2 is not outside of the predetermined range, i.e. a signai event has not been recorded, during the sensing period. This wouid inform a user if the sensor 2 is not responding as expected.

The test apparatus 1 further comprises a controller 6 adapted to control the flow of current through the wire resistor 3. In this example the controller 6 controls the magnitude of the current provided to the wire resistor 3, consequently controlling the intensity of photons generated by the wire resistor 3. Controlling the current in this manner allows for the simulation of objects at a range of distances from the sensor 2 without moving either the wire resistor 3 or the sensor 2. It will be appreciated that if only the detection of photons is of interest, and not any measurement of intensity, then the controller 6 may be configured to provide current at a fixed magnitude only. An additional advantage of using a wire resistor 3 as a source of infra-red radiation is that it can be controlled easily at low powers.

Further, the wire resistor 3 can trigger the pyroelectric sensor 2 a plurality of times in succession by providing current through the wire resistor 3 in pulses. In one embodiment, the controller 6 is configured to provide the current to the wire resistor 3 in one or more pulses. The duration of the pulses can be separated into two components: an on duration and an off duration. The on duration is the length of time for which current is provided to the wire resistor 3 and the off duration is the length of time for which current is not provided to the wire resistor 3 between two on durations. Commonly, when a pyroelectric sensor 2 is used in a PIR detector, a Fresnel lens is placed in front of the sensor 2. The Fresnel lens is split into a number of sections which focuses light onto the detector. Pulsing the generation of photons by pulsing the current provided to the wire resistor 3 simulates a heat source moving between sections of the Fresnel lens. Thus, altering the length of the pulses will allow the simulation objects moving at different speeds. In this example on durations and off durations between 0.6 and 2 seconds have been found to be particularly advantageous. The on duration of each pulse need not be equal to the off duration.

In this example the comparator 5 and the controller 6 are the same device however it will be appreciated that these may be two separate devices.

As shown in the embodiment of Figure 1, the test apparatus 1 comprises a housing 7 adapted to receive the wire resistor 3. In this example, a recessed portion 8 in the housing 7 serves as an isolator adapted to substantially isolate the pyroelectric sensor 2 from ambient sources of infra-red radiation when at least the sensing surface 4 of the sensor 2 is received within the recessed portion 8. While in this example a recessed portion 8 acts as an isolator, alternative means of substantially isolating the sensor 2 from ambient sources of infra-red radiation are readily available to the skilled person, such as extending wall portions configured to extend from the housing 7 or be separately placed to surround the sensor 2. The wire resistor 3 is disposed within the recessed portion 8, in this case on the base of the recessed portion 8. The sensing surface 4 of the heat sensitive surface is adapted to face the wire resistor 3 such that the generated photons are incident thereon.

The housing 7 further comprises a locator for locating the heat sensitive sensor 2 at a predetermined position. In the example of Figure 1, the predetermined position is a fixed distance from the wire resistor 3 such that at least the sensing surface 4 of the pyroelectric sensor 2 is received within the recessed portion 8. The distance between the wire resistor 3 and the pyroelectric sensor 2 may vary between test apparatus, however in this case the predetermined distance is between 2 and 8 mm. The locator comprises a support member 11 which is connectable to the housing 7. In this case the support member 11 is a printed circuit board which provides mechanical support to the pyroelectric sensor 2 along with circuitry and additional electronic components required fortesting the sensor 2. In another embodiment, the support member 11 provides mechanical support only to the pyroelectric sensor 2 and electrically connects the sensor 2 to further circuitry located elsewhere, for example with the comparator 5. In this example the controller 6 and the comparator 5 are stored within the housing 7.

The locator 10 is connectable to the housing 7 via connector pins 12. Proper engagement of the support member 11 with the connector pins 12 results in the pyroelectric sensor 2 being located at the predetermined distance from the wire resistor 3. In this example the connector pins 12 are disposed on the housing 7, although in alternative embodiments they may be part of the housing 7 or part of the locator 10. A plurality of connector pins 12 are shown in Figure 1, however it will be appreciated that a single connector pin 12 may be sufficient in order to provide engagement means for the locator 10. In this example the connector pins 12 are electrically conductive and provide, via the support member 11, an electrical connection between the pyroelectric sensor 2 and the comparator 5 and/or the controller 6.

It will be appreciated to a person skilled in the art that the test apparatus 1 need not include the sensor 2 nor its support member 11 but rather that these are required only when the test apparatus 1 is in use when testing a pyroelectric sensor 2. Instead, the test apparatus is adapted to receive these components. These features have been included in the description and the drawings in order to illustrate their relative positions to the test apparatus 1.

With reference to Figure 2, a method 13 for testing the pyroelectric sensor 2 comprises: supplying 14 a current to the wire resistor 3 in proximity to the pyroelectric sensor 2; measuring 15 an operational parameter of the heat sensitive sensor 2; and determining 16 if the operational parameter is outside of a predetermined range.

In this example, the current is supplied and controlled by the controller 6. The step of supplying 14 a current is therefore preceded by the step of controlling the controller 6 to supply a current. In some embodiments the step of supplying 14 the current to the wire resistor 3 comprises supplying a current to the wire resistor 3 a plurality of discrete times. Supplying 14 a current to the wire resistor 3 results in the step of exposing the sensing surface 4 of the pyroelectric sensor 2 to infra-red photons. The steps of measuring 15 the operational parameter and determining 16 if the operational parameter is outside of a predetermined range are performed by the comparator 5 in this example. In this example the method is carried out using the test apparatus 1 of Figure 1. The method includes the step of substantially isolating the heat sensitive sensor 2 from ambient sources of infra-red radiation which is achieved in this example by locating the sensor 2 within the recessed portion 8 of the housing 7. Substantially isolating the sensor 2 from ambient sources of infra-red radiation increases the reliability of each test by removing potential sources of noise so that signal events are more readily observed. In order to further improve the reliability of the measurements, the method may comprise the step of locating the pyroelectric sensor 2 at a predetermined distance from the wire resistor 3. In this example, the method comprises the step of indicating that the operational parameter is outside of the predetermined range.

Claims

1. A test apparatus for triggering a heat sensitive sensor, comprising a wire resistor.

2. The test apparatus of claim 1 wherein the wire resistor is configured to emit photons substantially in the infra-red range.

3. The test apparatus of claim 1 or claim 2 wherein the wire resistor is a wound wire resistor.

4. The test apparatus of any preceding claim comprising a comparator adapted to compare an operational parameter of the heat sensitive sensor to a predetermined range.

5. The test apparatus of any preceding claim comprising a controller adapted to control the flow of current through the wire resistor.

6. The test apparatus of claim 5 wherein the controller is configured to provide current to the wire resistor in discrete pulses.

7. The test apparatus of claim 6 wherein the duration of each discrete pulse is between 0.5 - 2 seconds.

8. The test apparatus of any preceding claim further comprising a housing adapted to receive the wire resistor.

9. The test apparatus of claim 8 wherein the housing comprises a recessed portion adapted to receive the heat sensitive sensor.

10. The test apparatus of claim 8 or any claim dependent thereon wherein the housing comprises a locator for locating the heat sensitive sensor at a predetermined position.

11. The test apparatus of claim 10 wherein the predetermined position is between 2 - 8mm from the wire resistor.

12. The test apparatus of any of claims 10 or any claim dependent thereon wherein the locator comprises a support member connectable to the housing.

13. The test apparatus of any of claims 12 or any claim dependent thereon wherein the support member comprises a printed circuit board.

14. A method for testing a heat sensitive sensor comprising: supplying a current to a wire resistor in proximity to a heat sensitive sensor; measuring an operational parameter of the heat sensitive sensor; and determining if the operational parameter is outside of a predetermined range.

15. The method of either of claim 14 wherein the step of supplying a current is preceded by controlling the controller to supply a current.

16. The method of claim 14 or any claim dependent thereon comprises the step of exposing the heat sensitive sensor to infra-red photons after the step of supplying a current to a wire resistor.

17. The method of any of claim 14 or any claim dependent thereon comprises the step of locating the heat sensitive sensor at a predetermined distance from the wire resistor.

18. The method any of claim 14 or any claim dependent thereon wherein the step of supplying a current to the wire resistor comprises supplying a current to the wire a plurality of discrete times such that pulses of infra-red radiation are emitted by the wire resistor.

19. The method of any of claim 14 or any claim dependent thereon comprising the step of, indicating that the operational parameter is outside of the predetermined range.

20. A test apparatus substantially as described herein with reference to the accompanying drawings.

21. A method for testing a heat sensitive sensor substantially as described herein with reference to the accompanying drawings.