Pulse generator device and method for evaluating a sensor break

Abstract

An electronic device having at least one connector for at least one wired sensor. The device has a sensor break detection unit, wherein the sensor break detection unit comprises a pulse generator outputting pulses of different polarity being adapted to output at least one electrical signal to the wired sensor and detector means for detecting a response signal from the wired sensor.

Claims

1. An electronic device, adapted to be supplied with voltage from a mains supply having a frequency, the device having at least one connector for at least one wired sensor, the device comprising a sensor break detection unit, the sensor break detection unit having a pulse generator being adapted to output at least one electrical signal to the wired sensor and detector means for detecting a response signal (SB.sub.+, SB.sub.) from the wired sensor wherein said at least one electrical signal output by the pulse generator includes at least two pulses having different polarity.

2. The device according to claim 1, wherein said at least one electrical signal output by the pulse generator includes two pulses within a time span being selected from approximately 40% to approximately 60% of a full cycle of the frequency of the mains supply from which the electronic device is supplied with voltage.

3. The device according to claim 1, wherein said detector means comprise at least one Analog/Digital-Converter and wherein said detector means are adapted to execute at least one measurement cycle selected from one or more of the following: at least one measurement of a predefined main input value (MIV) denoting a measurement of a data of interest sensed by the wired sensor before the pulse generator outputs the at least one electrical signal including the at least two pulses during the measurement cycle, at least one measurement of the response signal (SB.sub.+, SB.sub.), and if the wired sensor comprises a thermocouple, at least one measurement of a cold junction temperature (CJ) of the connector measured by a cold junction temperature sensor after the pulse generator outputs the at least one electrical signal including the at least two pulses during the measurement cycle.

4. The device according to claim 3, having an evaluation circuit being adapted to calculate a sensor break value (SB.sub.val) from the difference of the at least one response signal (SB.sub.+, SB.sub.) and the main input value (MIV) according to the following formulae:
SB.sub.val=SBMIV or
SB.sub.val=SB.sub.++SB.sub.2.Math.MIV,

5. The device according to claim 4, wherein the evaluation circuit is adapted to calculate a first order moving average (SB.sub.filt1) of the sensor break value (SB.sub.val) using a predefined time constant (SB.sub.TC) according to the following formula: ${\mathrm{SB}}_{\mathrm{filt}1}={\mathrm{SB}}_{\mathrm{filt}1}+\frac{{\mathrm{SB}}_{\mathrm{val}}-{\mathrm{SB}}_{\mathrm{filt}1}}{{\mathrm{SB}}_{\mathrm{TC}}}.$

6. The device according to claim 5, wherein the evaluation circuit is adapted to calculate a second order moving average (SB.sub.filt2)) of the sensor break value (SB.sub.val) using the time constant (SB.sub.TC) according to the following formula: ${\mathrm{SB}}_{\mathrm{filt}2}={\mathrm{SB}}_{\mathrm{filt}2}+\frac{{\mathrm{SB}}_{\mathrm{filt}1}-{\mathrm{SB}}_{\mathrm{filt}2}}{{\mathrm{SB}}_{\mathrm{TC}}}.$

7. The device according to claim 6, wherein the evaluation circuit is adapted to calculate a modulus difference between the raw sensor break value (SB.sub.val) and any of the first order or the second order moving averages (SB.sub.filt1, SB.sub.filt2) and wherein the evaluation circuit (4) is adapted further to compare the result with a predefined first threshold value (TH.sub.1).

8. The device according to claim 1, wherein the evaluation circuit is adapted to reject a sensor break signal if a resulting value of a modulus calculation of two or more consecutive measurements of the main input value (MIV) is greater than a predefined second threshold value.

9. A method for detecting a break of at least one wired sensor, the method comprising: sensing a mains supply voltage having a frequency, supplying at least one electrical signal to the wired sensor by means of a pulse generator, wherein the at least one electrical signal includes at least two pulses having different polarity, and receiving a response signal (SB+, SB) from the wired sensor within a time span selected as a function of the mains supply voltage frequency, wherein a predefined difference between the response signal and a predefined main input value (MIV) is indicative of a break of the at least one wired sensor, wherein the main input value (MIV) denotes a measurement of a data of interest sensed by the wired sensor.

10. The method according to claim 9, wherein the at least two pulses are supplied within the time span being selected from approximately 40% to approximately 60% of a full cycle of the frequency of the mains supply.

11. The method according to claim 9, further comprising executing at least one measurement cycle comprising at least one measurement of the predefined main input value (MIV) denoting a measurement of a data of interest before said supplying the at least one electrical signal, at least one measurement of the response signal (SB.sub.+, SB.sub.), and optionally at least one measurement of a cold junction temperature (CJ) after said supplying the at least one electrical signal.

12. The method according to claim 9, further comprising calculating a sensor break value (SB.sub.val) from the difference of the at least one response signal (SB.sub.+, SB.sub.) and the main input value (MIV) according to the following formulae:
SB.sub.val=SBMIV or
SB.sub.val=SB.sub.++SB.sub.2.Math.MIV.

13. The method according to claim 9, further comprising calculating by means of an evaluation circuit a first order moving average (SB.sub.filt1) of the sensor break value (SB.sub.val) using a time constant (SB.sub.TC) according to the following formula: ${\mathrm{SB}}_{\mathrm{filt}1}={\mathrm{SB}}_{\mathrm{filt}1}+\frac{{\mathrm{SB}}_{\mathrm{val}}-{\mathrm{SB}}_{\mathrm{filt}1}}{{\mathrm{SB}}_{\mathrm{TC}}},$ and calculating by means of the evaluation circuit an optional second order moving average (SB.sub.filt2) of the sensor break value (SB.sub.val) using the time constant (SB.sub.TC) according to the following formula: ${\mathrm{SB}}_{\mathrm{filt}2}={\mathrm{SB}}_{\mathrm{filt}2}+\frac{{\mathrm{SB}}_{\mathrm{filt}1}-{\mathrm{SB}}_{\mathrm{filt}2}}{{\mathrm{SB}}_{\mathrm{TC}}}.$

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention may be more easily understood and better appreciated when taken in conjunction with the accompanying drawing, in which:

(2) FIG. 1 illustrates one embodiment of an electronic device according to the invention.

(3) FIG. 2 illustrates one embodiment of the timing of pulses used for sensor break detection according to the invention.

(4) FIG. 3 illustrates one embodiment of the timing of data acquisition.

(5) FIG. 4 illustrates a flow chart of one embodiment of a method according to the invention.

DETAILED DESCRIPTION

(6) The following description is merely exemplary and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principle of the present disclosure.

(7) Looking now at FIG. 1, an exemplary embodiment of an electronic device 1 is shown. The electronic device 1 may consist of or comprise a data logger, a control circuit or a feedback control circuit. In some embodiments, the electronic device 1 is a temperature controller.

(8) The electronic device 1 has at least one connector 26 for at least one wired sensor 2. The wired sensor 2 may generate a voltage in response to changing ambient conditions. In other embodiments of the invention, the sensor 2 may change its electrical resistance in response to changing ambient conditions. In some embodiments of the invention, the sensor 2 may comprise any of a thermo couple, a resistance thermometer, a hot-wire mass flow meter or a hot-wire anemometer. It should be clear to one of ordinary skill in the art that the sensors mentioned are not limiting the invention. Those skilled in the art will apply the principles disclosed easily to any other known sensor.

(9) The sensor 2 has two wires 21 and 22 which are intended to supply electrical signals from the sensor 2 via the connector 26 to the electronic device 1. In other embodiments of the invention, the sensor 2 may have a greater number of wires. In some embodiments of the invention, the number of wires may amount 2, 3 or 4.

(10) If the wired sensor 2 comprises a thereto couple, the connector 26 constitutes the cold junction of the voltage generating circuit. In order to enhance accuracy of the temperature measurement, the temperature of the cold junction can be measured by at least one cold junction temperature sensor 25. In some embodiments, the cold junction temperature sensor 25 may comprise a platinum thermometer or any other type of resistance thermometer.

(11) The signal generated by the sensor 2 connects to an input of detector means 32. Detector means 32 are provided to gather at least one main input value of the sensor 2, e.g. a wind speed, a flow or a temperature. Furthermore, detector means 32 are adapted to detect a response signal for calculating a sensor break value.

(12) In the embodiment shown, detector means 32 comprise at least one analog/digital converter 320. The analog/digital converter 320 may have a resolution from 16 bits to 24 bits in order to ensure high quality measurements with low errors. The ADC 320 is adapted to generate a digital data stream representing the data of the sensor 2.

(13) Furthermore, detector means 32 may comprise an optional multiplexer 325. The multiplexer 325 may allow data acquisition from a plurality of sensors 2 with a single ADC 320. In other embodiments of the invention, every sensor 2 out of plurality of sensors may have a dedicated ADC 320, so that data acquisition may be performed at higher data rate. In theses cases, a multiplexer 325 may be omitted.

(14) The digital data stream digital data stream from the ADC 320 is supplied to an evaluation circuit 4. The evaluation circuit 4 may comprise a memory 42. The memory 42 may comprise any of a DRAM or a flash memory or a hard drive to store acquired data.

(15) Furthermore, the evaluation circuit 4 may comprise a microprocessor 41. The microprocessor 41 may be adapted to calculate at least one sensor break value being indicative of the health status of the sensor 2. In some embodiments, the microprocessor 41 may calculate a plurality of sensor break values. In some embodiments, the microprocessor 41 may be adapted to validate a plurality of sensor break values in order to increase accuracy and to avoid false sensor break signals.

(16) Furthermore, an optional display 44 may be present to visualize acquired data. In some embodiments, an optional interface 43 may be present to supply sensor data and/or to signal a sensor break to machinery comprising the electronic device 1.

(17) To perform sensor break detection, a pulse generator 31 is present. The pulse detector 31 and detector means 32 are part of a sensor break detection unit 3. The pulse detector outputs at least one electrical signal to the wired sensor 2. The electrical signal may comprise at least one current pulse or at least one voltage pulse, The raw signal outputted by the pulse generator is altered by the impedance of the connector 26 and the sensor 2. This altered signal is detected by the ADC 320, After a sensor break, the impedance of the sensor 2 changes, which causes a change of the response signal detected by the ADC 320. These changes of the response signal are assessed by the evaluation circuit 4 and a sensor break may be signaled.

(18) With respect to FIG. 2 and FIG. 3, exemplary embodiments for electrical signals and timing diagrams are shown.

(19) The upper part of FIG. 2 illustrates a timing diagram for a first sensor being attached to a first input channel of the electronic device 1. The lower part of FIG. 2 illustrates a timing diagram for a second sensor being connected to a second channel of the electronic device 1. Both channels can be connected to a single ADC by means of a multiplexer 325. In other embodiments two ADCs 320 may be present, so that each channel has a dedicated ADC 320 for signal conversion.

(20) Looking at channel 1, an exemplary measurement cycle starts with a measurement of a main input value MIV. The main input value denotes a measurement of the data of interest, e.g. a temperature, if the sensor 2 is a temperature sensor. In some embodiments of the invention, the measurement of the main input value may take between 40 ms and 80 ms. In the exemplary embodiment shown in FIG. 3, measurement of the main input value takes 66.552 ms.

(21) After the main input value measurement has been finished, the pulse generator 31 generates a voltage pulse on the sensor connector. Reference 50 of FIG. 2 shows the voltage pulse as seen on the wires 21 and 21 during an open circuit condition. In some embodiments of the invention, the peak voltage may be smaller than 120 mV, so that interference with other devices or disturbance of a digital data bus can be avoided. Furthermore, the power dissipation inside the sensor 2 is negligible small, so that disturbance of the measurement of the main input variable can be avoided.

(22) Line 6 of FIG. 2 illustrates the response signal as seen by the ADC 320 during an open circuit condition of the sensor 2. Due to the sample-and-hold stage of the ADC acting as a low pass filter, only one half of the wave form generated by the pulse generator 31 is seen by the ADC. The response signal 6 is converted into a digital value by the ADC 320 and supplied to the memory 42 of the evaluation circuit 4.

(23) After pulse generation and measurement of the response signal, an optional measurement of a cold junction temperature CLT or a measurement of a common mode voltage can be performed.

(24) After having reached a settled region 55 within a time span t.sub.1, the A/D conversion sequence starts again with the measurement of a main input variable MTV. In some embodiments of the invention, the pulse generator may be adapted to output pulses having different polarity, so that the second measurement is performed with a second pulse 51 having different polarity then the first pulse 50.

(25) The repetition rate of the A/D conversion sequence is indicated as time span t.sub.1 in FIG. 2. In some embodiments of the invention, t.sub.1 may be selected from approximately 110 ms to approximately 300 ms. In other embodiments, T.sub.1 may be selected from approximately 200 ms to approximately 250 ms. In still another embodiment, t.sub.1 may amount approximately 220 ms.

(26) If a multiplexer is used, values from channel 2 may be acquired with a phase shift, so that data from channel 2 is acquired during the relaxation time of channel 1 and vice versa.

(27) FIG. 3 shows an alternative timing diagram for an A/D conversion sequence. This timing diagram comprises measurement of a main input value MIV and subsequent measurement of two sensor break signals. The sensor break signal for a positive pulse SB.sub.+ and the sensor break signal from a negative pulse SB.sub. are acquired within a time span of 18.75 ms. This time is selected to match approximately a full cycle of a mains supply frequency, so that noise from the mains supply may be suppressed by adding both values. The selected time span is higher than the optimum value needed for a 50 Hz mains supply but lower than the optimum value needed for a 60 Hz mains supply, so that the device is equally suited for 50 or 60 Hz mains. Those skilled in the art will easily adjust this timing if a supply voltage having different frequency is used, e.g. on a railroad loco or on board of a plane.

(28) FIG. 4 illustrates the generation of a sensor break signal from the measured response: signal by the evaluation circuit 4.

(29) As can be easily appreciated from FIGS. 2 and 3, measurement of a sensor break value SB is disturbed by the main input value MIV, as the sensor continuously delivers data. On the other hand, measurement of the main input value MIV is not disturbed by the sensor break signal, as MIV measurement is carried out when the pulse generators 31 is switched off. Therefore, a sensor break value SB.sub.val is corrected in a first method step 71 by subtracting the main input value. If a plurality of response signals SB.sub.+ and SB.sub. is taken, a corresponding number of main input values will be subtracted.

(30) In a subsequent second method step 72, the raw value calculated in the first method step 71 is filtered for noise rejection. The time constant SB.sub.TC applied is chosen to afford maximum noise rejection whilst still maintaining a reasonable response time, e.g. less than 0.25 s. Optionally, a two-stage filtering may be applied to improve noise rejection.

(31) As the raw sensor break value SB.sub.val is derived from three separate measurements, the algorithm may be susceptible to input signal transients during the measurement cycle. Therefore, the third method step 73 is carried out to reject such potential disturbances. The third method step 73 comprises a calculation of the modulus of the difference between the raw sensor break value SB.sub.val and the current filtered value SB.sub.filt2. The resulting value is compared against a first threshold value TH.sub.1 and if it is found to be greater, a false sensor break detection is rejected.

(32) As protection against low frequency input clewing causing false sensor break detections, a fourth method step can be performed. This fourth method step 74 comprises calculating the modulus of the difference between two consecutive main input measurements. The resulting value is compared against a second threshold TH.sub.2. If it is found to be greater, a false sensor break detection is rejected.

(33) In the fifth method steps 75, the filtered value SB.sub.filt2 of the sensor break signal is compared against a third threshold TH.sub.3 being indicative for a sensor break.

(34) In the sixth method step 76, the filtered value SB.sub.filt2 of the sensor break signal is compared against a fourth threshold TH.sub.4. This fourth threshold indicates an open circuit.

(35) Finally, a sensor break signal of high accuracy can be generated in the last method step 77. The method shown in FIG. 4 has the advantage of reasonable response times and low error rates, i.e. false-positive or false-negative sensor break signals are avoided.

(36) Obviously, readily discernable modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practice otherwise then as specifically described herein. For example, while describing the invention in terms of discrete components interactively cooperating, it is contemplated that the system described herein may be practiced entirely in software or by means of an application specific integrated circuit (ASIC). Software may be embodied in a carrier such as a magnetic or an optical disc, or a radio frequency carrier wave.

(37) Those skilled in the art can now appreciate from the foregoing description that a broad teaching of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.