DE2603797A1 - PROCEDURE FOR CHECKING A THERMOELEMENT AND DEVICE FOR ITS IMPLEMENTATION - Google Patents

Description

DIPL ..- ING. H. MARSCH 4 Düsseldorf,

DIPL.-ING. K. SPARING 260 3 797 and bmanxstrassb 31

BOX 140147

PATENT LAWYERS TELEPHONE (0211) 072216

48/67

description
to the patent application

of The Solartron Electronic Group Limited, Victoria Road _f Farnborough, Hampshire / England

concerning:

"Procedure for checking a thermocouple and the device for carrying it out"

The invention relates to a method and a device for checking thermocouples or Thermocouples, especially those thermocouples that interact with a data processing system.

A typical data processing system in the sense used here is connected to a large number of thermocouples, which are each arranged at an assigned point of a plant, such as a power plant or a chemical plant, which is to be monitored by the data processing system. A data processing system in this sense could also be called a process control can be referred to. Each thermocouple can be selectively connected to a measuring device, such as a digital voltmeter, which forms part of the data processing system and measures the respective thermal EMF that is generated by the thermocouple, all the more so the associated temperature at the various points determine where the thermocouples are located. From time to time it is possible that one or the other thermocouple

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damaged, e.g. during its relocation to another point in the system. If the damage causes the If the thermocouple circuit is interrupted, this can be determined without further ado. However, it is possible that the damage causes the thermocouple to have a higher than normal resistance rather than simply breaking the circuit is. In this case the thermocouple can then continue to produce a seemingly normal output EMF, i.e. an output EMF within its normal operating range, which is nonetheless incorrect, and the temperature at which the thermocouple is exposed, does not reflect correctly. The object of the present invention is to provide a method and a device to create its implementation, with which thermocouples, connected to a data processing system or checked can be tested. The method according to the invention is summarized in claim 1, while claims 2 to 4 define preferred training courses. The apparatus for performing the method is in its most general form in Claim 5 defines, while the following subclaims define preferred developments of the device.

An exemplary embodiment of the subject matter of the invention will be described in greater detail below with reference to the accompanying drawings explained; this represents a block diagram of the device which is intended for the use of a data processing system for the purpose of checking thermocouples in the data processing system assigned.

The device, which is shown in the drawing and designated as a whole with 10, forms part of a data processing system. The device 10 comprises a pair of input terminals 11, 12 which, in use, are connected for CM reception the output voltage generated by a thermocouple 14 with

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a hot point 16 and a cold point 18. For convenience only a single thermocouple is shown, although in practice it is typically used in a data processing system a plurality of thermocouples can be selectively connected to the input terminals 11, 12 by means of a scanning unit is.

The terminals 11, 12 are connected within the device 10 to the input terminals 20, 21 of an analog-to-digital converter 22 connected, which has a control input 24 and an output 26. The transducer 22 is designed so that it is at the output 26 when a control signal is applied to the control input 24, a digital output signal is generated which is representative of the size of the voltage that is applied to its input terminals 20, 21.

The terminals 11, 12 are also connected to the outputs 32, 34 of a constant current source 36 via corresponding switches 28, 30. The switches 28, 30 are typically designed as reed relays ¹ .

The output 26 of the converter 22 is connected to a changeover switch which has a first switch position in which the Output 26 is connected to input 39 of a digital memory 40; in a second switch position it connects the output 26 with an input 42 of a digital subtraction circuit 44. The memory 40 has a control input 45 and an output 46 is connected to a further input 48 of the subtracting circuit 44.

The subtraction circuit 44 has a control input 49 and an output 50 which is connected to a changeover switch 52 is. The changeover switch 52 has a first switch position in which it connects the output 50 to the input 54 of a further digital memory 56 connects, as well as a second switching position in which it connects the output 50 with a comparison input 58 of a digital

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Comparator 60 connects. The memory 56 has a control input 61 and an output 62 which is connected to another comparison input 64 of the comparator 60. The comparator 60 has a control input 65.

The comparator 60 also has an output 66 to which it transmits a signal corresponding to a logic level "1" when the digital signals applied to its inputs 58, 64 differ by more than a predetermined amount; if those Digital signals do not differ from one another by more than this predetermined amount, the comparator 60 generates at its output 66, a signal corresponding to a logic "0" level. The signal at the output 66 of the comparator 60 forms the output signal of the device 10.

The device 10 further comprises a sequence control circuit 70 with a set input 71, a test start input 72 and a plurality of control outputs 73, 74, 75, 76 and 77: The control output 73 is connected to the control input 23 of the Converter 22; the control output 74 is connected to the switches 28, 30, 38 (as indicated by the arrows 78); the control output 75 is connected to the control inputs 45, 49 of the Memory 40 or the subtracting circuit 44, the Steuerausqanq 76 is connected to the switch 5 2 (as indicated by an arrow 79), and the control output 77 is connected to the Control inputs 61, 65 of the memory 56 and the comparator 60, respectively. The sequence control circuit 70 will not be discussed in detail since it is essentially only one source for clock pulses, at least one counter and a plurality of logic gate circuits and bistable circuits, all in Conventionally designed so that the control outputs 73-77 during predetermined time periods and in a predetermined Sequence are excited, as explained below.

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In operation and at a time when it is known that the thermocouple 14 is working properly and at a stable Temperature, the thermocouple 14 is connected to the input cables 11, 12 of the device 10. To the operation of the device 10 initiate, a pulse is applied to the set input 71 of the sequence control circuit 70, and this If necessary, a pulse causes all switches 28, 30, 38, 52 to be switched to the switch positions shown in FIG will. The output voltage V1 generated by the thermocouple 14, which output voltage is the thermal emf, generated by the thermocouple, g is accordingly applied to the input terminals 20, 21 of the transducer 22.

Shortly after this first pulse, the sequence control circuit 70 generates a "digitization control pulse" at its control output 73, which is applied to the control input 24 of the converter 22 and causes it to generate a first digital signal ν, _ at its output 26, which is representative of the magnitude of the voltage V ,. Accordingly, it can be seen that the digital signal V, _{D is} representative of the magnitude of the thermal EMF generated by the thermocouple 14. This first digital signal V _1D is input into the memory 40 by means of the switch 38.

Shortly after the digital signal V, _{Q has} been stored in the memory 40, the sequence control circuit 70 generates a signal at its control output 74 with which all switches 28, 30, 38 are switched to the respective other switch position (not shown in the drawing). The constant current source 36 is accordingly applied and allows a known current I to flow through the thermocouple 14. The thermocouple now generates an output voltage V ₃ , which represents the sum of its thermal emf, V, and a voltage V-, generated across the thermocouple

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by the flow of the known current K, this voltage V _{3 being} given as IR, with R being the resistance of the thermocouple 14 when it is operating correctly. Shortly thereafter, the sequence control circuit 70 generates a further "digitizing control pulse" at its output 73, which causes the converter 22 to generate a second digital signal V _Q2 , representative of the magnitude of the voltage V_, at its output 26. This second digital signal is applied to the input 42 of the subtraction circuit 44 by means of switch 38. The time interval between the generation of the first and second digital signals is typically less than one second, so that the temperature of the thermocouple 14 can be regarded as constant with a high degree of probability.

The sequence control circuit 70 then generates a pulse at its output 75 which causes the digital signal is read out in the memory 40, and is applied to the other input 48 of the subtracting circuit 44, wherein the same pulse also causes the subtraction circuit to algebraisii one of the two digital signals at its inputs 42, 48 subtracted from the other. The subtracting circuit 44 accordingly generates a value at its output 50 digital difference signal which is representative of the result of this subtraction and therefore representative of the Size of the voltage V_ - V. = V- = IR: This digital difference signal is written into the memory 56 via the switch 52. As a result, the memory 56 now contains a digital signal which is representative of the magnitude of the resistance of the thermocouple 14 at the point in time when it is known that it is working correctly.

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In order to then check or test the thermocouple 14, a pulse is applied to the test start input 72 of the sequence control circuit 70, with which the switch 52 is switched to its switching position, not shown, and the other switches 28, 30, 38 to the one shown Switch positions are brought. The above-described sequence of processes for generating the first and second digital signals and for deriving a digital difference signal therefrom then runs again, but the digital difference signal is now applied to comparison input 58 of comparator 60 via switch 52. The sequence control circuit 70 then generates a pulse at its output 77 with which the digital signal in the memory 56 is read out without deletion and is applied to the other comparison input 64 of the comparator 60, the same pulse also causing the comparator to display the digital signals its inputs 58, 64 checked. If the resistance of the thermocouple 14 has not changed significantly, which means that the thermocouple is still operating reliably, the comparator 60 produces the above-mentioned logic level "0" signal at its output 66, while if the resistance of the thermocouple has changed significantly has changed, the I '<■ arator 60 a Loqikneqel "1" Sianal at its Ausqanq -: i. Lt This latter signal can be used to trigger an Al, ζ.Γ, an 'iarmlamno, -if' ewished.

■> t! I 'ipsamte Pri: ⁴ ier test procedures, the ^ ben described' · ■ ' χ, is repeated from time to time to bring about a subsequent end * τ 1 ".: R.checking of the thermocouple 14, and can be initiated by urine and / or by a timer unit which forms part of the data processing system It does not matter that the temperature of the thermocouple 14 is different for each test, since the thermal emf generated by the thermocouple is independent is compensated for by the subtraction of its size.

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To provide for :; a plurality of thermocouples too meet, it is only necessary to train the capacity of the memory 56 so that a corresponding digital difference signal can be stored for each thermocouple, and to train the sequence control circuit so that initially the entire sequence of operations in response to the first pulse applied to input 71 for each thermocouple is carried out separately, and secondly, the entire sequence of switching operations in response to each test start pulse is repeated for each thermocouple (the memory 56 being properly controlled for each thermocouple or addressed). Alternatively, the capacity of the memory 40 and the sequence control circuit can also be increased 70 can be arranged to cause a corresponding first digital signal derived from each thermocouple to be entered sequentially into the memory 40, the switches 28, 30 in the illustrated switching position stand. The sequence control circuit 70 is then operated so that the switches 28, 30 flipped into their other switching positions and the transducer 22 is made to output a corresponding second S digital signal for each thermocouple for itself, with every second digital signal being subtractively combined in the subtraction circuit 44 with the associated first digital signal, read out from the memory 40 in order to generate a corresponding digital difference signal. These digital difference signals are either written into the memory 56 or applied to the comparator 60, depending on whether the generation was originally initiated by a pulse at input 71 or input 72 of the Sequence Control Circuit 70.

It can be seen that numerous modifications to the described embodiment of the invention are possible. In particular can with a computer-controlled data processing system or

the · in a data processing system, by a microprocessor

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with allocated memory is controlled, an appropriate one Current source, such as the source 36, can be provided, and then the method according to the invention can be carried out by corresponding Programming of the computer or the microprocessor can be carried out so that the data processing system the various carries out the required measurements in the correct sequence.

Further, while switches 38 and 52 are shown as simple mechanical switches, it should be understood that in practice they are designed as solid-state semiconductor switches.

(Patent claims)

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Claims (7)

Claims ; 1) j method for checking a data processing system connected thermocouple, characterized by the steps: - Generation of a first electrical output signal that is representative of the resistance of those who practice correctly Thermocouple, - Saving the first output signal, and - from time to time, a further electrical output signal is generated which is representative of the resistance of the thermocouple and comparing this further signal with the stored first signal for the purpose of Detection of a change in resistance. 2) Method according to claim 1, characterized in that the following steps are carried out for generating the first signal will: - Generating a first electrical measurement signal that is representative is for the size of the output voltage generated by the correctly working thermocouple, - Feeding a known current into the correctly working thermocouple and generating a second electrical measurement signal, this is representative of the magnitude of the output voltage generated by the known current through which the thermocouple flows, and - Combining the first and second measurement signals in such a way that a difference signal - representative of the difference in the respective quantities represented by the first and second measurement signals - is generated, which Difierenζsignal the forms the first output signal. - 11 - 609837/0652 3) Method according to claim 2, characterized in that for the generation of the further output signal the following steps must be carried out: - Generating a third electrical measurement signal, representative for the output voltage generated by the thermocouple, "Feeding the known current into the thermocouple and Generation of a fourth electrical measurement signal, representative of the magnitude of the known current flowing through it Thermocouple generated output voltage, and - Combining the third and fourth measurement signals in such a way that a further difference signal - representative of the Difference of the respective quantities represented by the third and fourth measurement signals - is generated, which further difference signal forms the further output signal. 4) Method according to claim 2 or 3, characterized in that the measurement signals are generated and combined digitally and the first and the other output signal as digital Signals are generated. 5) Device for use in a data processing system for checking a thermocouple connected to it, intended for carrying out the method according to one or more of the preceding claims, characterized by: - Circuits (22, 28, 30, 36, 38, 40, 44) for generating the electrical output signals, - a signal memory (56), - a signal comparator (60), and - a control circuit (70) for energizing the signal generator circuits such that the first output is generated and stored in the latch and from time at time thereafter in such a way that further output signals are generated and in the signal comparator with that in the signal memory stored are compared in order to determine a possible change in resistance of the thermocouple (14). 609837/0652 " ¹² " 26 (Π797 6) Device according to claim 5, characterized in that the signal generator circuits have a converter circuit (22) comprise for generating the electrical measurement signal which is representative of the magnitude of the thermocouple output voltage, a Current source (36) which can be connected to the thermocouple via switches (28, 30) for feeding in the known current, and a subtracting circuit (44), the control circuit (70) being adapted to control the signal generator circuitry initially excited to generate the first measurement signal, but at the same time disconnects the current source from the thermocouple, then the current source switches on to the thermocouple with the generation of a second measurement signal by the signal generator circuits, and finally energized the subtracting circuit to form the Difference between the first and the second measurement signal as the first electrical output signal. 7) Device according to claim 6, characterized in that the signal generator circuits have an analog-to-digital converter (22), by means of which the analog output voltage of the thermocouple (14) is converted into a representative of its size Transformed digital signal 609837/0652