JPH0462439A - Wire breaking detecting circuit of temperature measuring instrument - Google Patents

Abstract

PURPOSE:To speedily and accurately detect the wire breaking of a thermocouple, etc., by enabling the wire breaking detection while an input filter circuit is disconnected. CONSTITUTION:When the wire breaking is detected, an analog switch 9 is turned off and an analog switch 10 is turned on. When the switch 9 is turned off, the charging capacitor 5 of the filter circuit is disconnected from a power source 6, so the voltage at an input terminal 2 rises abruptly to the voltage of the power source 6 in the case of the wire breaking, but when no wire breaking is caused, the voltage is as high as the value of the thermo-electromotive force of the thermocouple 1 and up to about 100mV. Thus, when the switch 9 is turned off while the switch 10 is turned on, the wire breaking can be detected speedily at the output terminal of an amplifier 11 according to the voltage state of the input terminal 2 in the case of the wire breaking.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a disconnection detection circuit for a temperature measuring device, and particularly to a temperature detecting circuit such as a thermocouple or the like in an intelligent temperature measuring device equipped with a microcomputer. This invention relates to an improvement in a disconnection detection circuit that detects disconnection in electrical wiring.

[Conventional technology]

When detecting the temperature of a process, a temperature measurement device is generally used that uses a temperature detection element such as a thermocouple or a resistance temperature detector as a detection end. Thermocouples measure temperature using thermoelectromotive force, and resistance temperature sensors measure temperature by capturing changes in resistance of metals such as platinum or copper due to changes in ambient temperature.

In temperature measuring devices, in the case of thermocouples, the voltage ranges from several mV to several 1
A minute thermoelectromotive force of 0 mV is amplified with a high-precision DC amplifier, and signal insulation is applied to create a process unified signal (4 to 20 mDC).
A or DC1~5■) etc. and output it.
It is converted into various transmission signals by conversion and digital processing. In the case of a temperature-measuring resistor, a current is passed through the temperature-measuring resistor, and the change in resistance value corresponding to temperature is converted into a voltage value, which is extracted, amplified, and subjected to various signal processing.

By the way, thermocouples and resistance thermometers in temperature measuring devices are exposed to high temperatures or subjected to temperature cycles for temperature measurement, so there is a possibility that they may break. Therefore, in order to maintain process safety, conventional temperature measuring devices are equipped with a disconnection detection circuit to quickly detect disconnections in thermocouples, etc., and are configured to issue an alarm when a disconnection occurs.

An example of the configuration of a conventional disconnection detection circuit will be explained based on FIG.

In FIG. 6, 1 is a thermocouple, 2.3 is a pair of input terminals, and an input filter circuit is constituted by a resistor 4 (resistance value Rs) and a capacitor 5 (capacitance value CS). Reference numeral 6 denotes a DC power supply (VB) for flowing a current for detecting disconnection, 'r a resistor (R11) for limiting the current for detecting disconnection, and 8 an amplifier for amplifying the output of the filter circuit. In the above configuration, when a disconnection occurs in the thermocouple 1 or in the electrical wiring therebetween, current from the power source 6 passes through the resistors 7 and 4 and is applied to the capacitor 5, where charging is performed. The terminal voltage of capacitor 5 gradually increases, and the output voltage of amplifier 8 increases accordingly. When the output of the amplifier 8 reaches a predetermined level, it is determined that a disconnection has occurred.

[Problem to be solved by the invention]

First, the filter circuit of the eight disconnection detection circuits described above will be explained. A filter circuit consisting of a resistor 4 and a capacitor 5 is used to remove inductive noise superimposed on the signal line, and normally has a time constant of several tens of m5 to several hundred m5, and is essential for temperature measurement devices. . Further, the amplifier 8 disposed after the filter circuit is normally required to have a function of amplifying a signal of 0 to 2 mV with an accuracy of 0.1% or less.

In recent years, an operational amplifier with low drift, low offset voltage, and low current has been used for this amplifier. In such an operational amplifier, the input offset current temperature drift is suppressed to a low value of, for example, several tens of pA (picoamperes).

By the way, if the measurement voltage is 0 to 2 mV and the accuracy is 0.1%, the input offset current temperature drift of the operational amplifier 8 is, for example, 10 pA/℃, and the input resistance R5 is 20Ω, how can you adjust it with the input resistance? Even if the ambient temperature is 10
A change in temperature causes a change of 2 μV, resulting in an error of 0.1% with respect to the above measurement range. Furthermore, in practice, there are other input offset voltage temperature drifts,
This has an even greater influence as an error factor. Therefore, in the filter circuit shown in FIG. 6, in order to obtain the necessary time constant, the resistance value RS of the resistor 4 is selected to be as small as possible, and the capacitance value CI of the capacitor 5 is increased. It is common to do so.

Next, the current applied to detect disconnection will be explained. Although it is desirable to wire the thermocouple to the temperature measurement circuit using thermocouple bare wire, it is expensive, so a wire called a compensation conductor is usually used. Considering the case where such wiring is installed over a long distance, the temperature measuring device must allow a signal source resistance of about 500 Ω to ensure accuracy, and the current for disconnection detection must be maintained at this allowable value of the signal source resistance. The value is determined. Assuming that the measurement voltage range is O to 2 mV as above, the tolerance is 500Ω, and the disconnection current is 4nA,
The signal resistance source causes a voltage drop of 2μ, resulting in an error of 0.1%.

As described above, the circuit elements Rs, Cs, RB, and VB shown in FIG. 6 are determined from the limits of the resistance value R9 of the resistor 4, the time constant of the filter circuit, and the current value for disconnection detection. Considering various conditions, R3 is set to 4,7 Ω, C6 is set to about 21 μF, RB is set to 47 MΩ, and 8 is set to about 119V. Let's consider a case where the thermocouple is disconnected while the thermocouple is set to such a value.

In this case, the initial condition is that the input voltage is OmV, and the disconnection is detected at 2.2 mV, which is 110% of the measurement range. When a disconnection occurs, the current from the power source 6 becomes a constant current, flows into the capacitor 5, and is charged. The time t required until a disconnection is detected is approximately 128 (seconds) according to the formula (Cs x 2.2 mV)/4 n A.

The circuit configuration of a disconnection detection circuit of a conventional temperature measuring device has characteristics in that it takes a long time to detect a disconnection, and the voltage for detecting a disconnection gradually changes. Therefore, when a thermocouple breaks and the output of the temperature measurement device gradually increases to detect this, the process control device, which takes in the output of the temperature measurement device and performs control operations, detects that the process temperature has increased. The possibility exists to determine and perform operations to reduce the temperature. Performing such operations lowers the temperature of the actual process, disrupts the process, and results in product failure.

In order to solve the above problem, an alarm point is set for the signal input on the process control device side, and a
When the power gradually increases, this alarm allows countermeasures such as suspending the above operations to be taken, but in this case, it is not a perfect countermeasure because it takes a long time to reach the alarm point.

In addition, in the above-mentioned disconnection detection method, when the temperature measurement range is changed, the input voltage range changes, but if we assume that this input voltage range is O~20mV and consider the operation at the time of disconnection, the circuit constant Assuming that it remains the same as before, the time it takes to shake out will be 1208, which is 10 times as long. Therefore, it is necessary to change the detection current depending on the measurement range.

As is clear from the above explanation, the disconnection detection circuit of the conventional temperature measuring device does not give sufficient consideration to increasing the speed of detecting disconnection of the current-to-current ratio element, and this has the problem of giving erroneous information.

An object of the present invention is to provide a disconnection detection circuit for a temperature measuring device that can quickly and accurately detect disconnections in temperature detection elements such as thermocouples and electrical wiring.

[Means to solve the problem]

The disconnection detection circuit of the first temperature measurement device according to the present invention includes at least one temperature detection element, a filter circuit that removes noise from the output signal of the temperature detection element, and a first temperature detection circuit that amplifies the output signal of the filter circuit. and a temperature measuring device configured to extract temperature information based on the output signal of the first amplifier, a switch means provided between the temperature detection element and the filter circuit, and a disconnection detection device in the temperature detection element. and a second amplifier connected to a terminal of the temperature detection element, and when a wire breakage is detected, the switch means is turned off and the wire breakage state is detected by the output of the second amplifier. configured.

The disconnection detection circuit of the second temperature measuring device according to the present invention includes, in the first configuration, a multiplexer that selects and takes in the output signals of the first and second amplifiers, and digitizes the output signal of the multiplexer. A/D converter and A/D
Equipped with digital signal processing means that inputs the output signal of the converter and performs signal processing for temperature measurement or wire breakage detection, and also controls the operation of the switch means and multiplexer, and selects temperature measurement processing and wire breakage detection processing by the digital signal processing means. configured to do so.

The disconnection detection circuit of the third temperature measurement device according to the present invention includes at least one temperature detection element, a filter circuit that removes noise from the output signal of the temperature detection element, and a filter circuit that amplifies the output signal of the filter circuit. In a temperature measurement device configured to extract temperature information based on an amplifier and an output signal of the amplifier, a switch means provided between the temperature detection element and the filter circuit, and a current for disconnection detection is supplied to the temperature detection element. The temperature detecting element has a power supply circuit connected to the terminal of the temperature detecting element, and is configured to turn off the switch means when a wire breakage is detected, and detect the wire breakage state using the output of the comparator.

The disconnection detection circuit of the fourth temperature measuring device according to the present invention includes, in the third configuration, an A/D converter that digitizes the output signal of the amplifier, and an output signal of the A/D converter and a comparator. A digital signal processing means is provided for inputting an output signal to perform signal processing for temperature measurement or wire breakage detection, and for controlling the operation of the switch means, so that temperature measurement processing and wire breakage detection processing are selectively performed by the digital signal processing means. configured.

The disconnection detection circuit of the temperature measuring device according to the present invention has a plurality of temperature detection elements in the second or fourth configuration, and a connection switching means is provided at the input terminal portion of each temperature detection element, and a digital signal It can be configured such that the processing means controls the switching operation of the connection switching means and selects and captures the output signal of the temperature detection element.

Further, in the disconnection detection circuit of the temperature measuring device according to the present invention, in each of the above configurations, another switch means is provided between the terminal of the temperature detection element and the output terminal of the power supply circuit, and a second switch means is provided between the terminal of the temperature detection element and the output terminal of the power supply circuit. The input terminal of the amplifier or comparator can be connected to the input terminal of the amplifier or comparator.

[Effect]

In the disconnection detection circuit of the temperature measuring device according to the present invention, a signal extraction route for temperature measurement and a signal extraction route for detecting disconnection of a temperature detection element such as a thermocouple are separate, and for this purpose, the temperature detection element and the input A switch means is interposed between the temperature detecting element and the filter circuit, and the switch means connects the temperature detection element and the filter circuit when measuring the temperature, and disconnects the temperature detecting element and the filter circuit when a disconnection is detected. With such a configuration,
When a wire breakage occurs, it is possible to rapidly raise a detection signal at the output terminal of the second amplifier configured to extract a signal representing the wire breakage state, and quickly determine whether or not there is a wire breakage. I can do it. Also, when a comparator is used instead of the second amplifier, a disconnection detection signal can be quickly obtained.

Temperature measurement processing or disconnection detection with digital signal processing means 8
Processing is executed. Therefore, the output signals from the first and second amplifiers are appropriately selected via the multiplexer and input to the digital signal processing means. When a comparator is used instead of the second amplifier, the output of the comparator can be directly input to the digital signal processing means, so the circuit configuration can be simplified.

When a plurality of temperature detection elements are provided, the connection switching means is configured to select a detection signal to be taken into the digital signal processing means.

In addition, another switch means is interposed between the output terminal of the power supply circuit for flowing the disconnection detection current and the temperature detection element, and the other switch means is turned off when measuring the temperature. This is to prevent errors caused by the signal source resistance from flowing into the temperature detection element.

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings.

A first embodiment of eight disconnection detection circuits for a temperature measuring device will be described with reference to FIG. In FIG. 1, the same elements as those shown in FIG. 6 are given the same reference numerals. In FIG. 1, 1 is a thermocouple which is a temperature detection element, 2 and 3 are input terminals, 4 is a resistor, 5 is a capacitor, and 4 and 5 form an input filter circuit. Reference numeral 6 denotes a power source that supplies a current for detecting disconnection, 7 a resistor that sets the value of the current, and 8 an amplifier. The wiring structure of the above circuit elements is the same as the structure described above. For such a structure, two further analog switches 9.10 and an amplifier (or comparator as described below)
11 is added. Analog switch 9 is interposed between input terminal 2 and resistor 4, and analog switch 10 is interposed between input terminal 2 and resistor 7. In addition, the amplifier 11
has the function of inputting the voltage at the downstream terminal of the resistor 7 and amplifying it. A disconnection detection voltage is taken out from the amplifier 110 output. The on/off operation of the analog switch 9.10 is performed by a control means (not shown). The analog switch 10 does not need to be provided when the voltage drop across the signal source resistance due to the disconnection detection current is ignored.

Next, the operation of the circuit shown in FIG. 1 will be explained. When measuring temperature, the analog switch 9 is turned on, and the thermoelectromotive force of the thermocouple 1 is input to the amplifier 8 via a filter circuit including a resistor 4 and a capacitor 5.

A temperature measurement signal is taken at the output of amplifier 8. At this time, the other analog switches 10 may be in either the on or off state. When detecting a disconnection, use the analog switch 9
is turned off, and the analog switch 10 is turned on.

When the analog switch 9 is turned off, the charging capacitor 5 of the filter circuit is disconnected from the power supply 6, so the voltage at the input terminal 2 will quickly rise to the voltage of the power supply 6 if a disconnection occurs, and the disconnection will occur. If it is not occurring, the value of the thermoelectromotive force of thermocouple 1 is the same as that of about 100 mV at most. When the analog switch 9 is switched from on to off with the analog switch 10 turned on in this way,
When a disconnection occurs, the disconnection can be quickly detected at the output end of the amplifier 11 based on the voltage state at the input terminal 2.

In the above case, the capacitor 5 included in the input filter circuit can be ignored, but the thermocouple 1
In some cases, the line capacitance of electrical wiring cannot be ignored. When the wiring becomes long and the line capacitance increases, it is necessary to increase the disconnection detection current so that the voltage rises quickly when the disconnection occurs. As described above, the analog switch 10 does not necessarily need to be provided, but if the disconnection detection current is to be increased, it is necessary to provide the analog switch 10 to eliminate errors caused by the signal source resistance.

For example, in the case of an electrical wiring with a line capacitance of 100 pF/m and a length of 100 m, the lumped constant will be 10' p
It becomes F. At this time, when the disconnection detection voltage in the amplifier 11 is 200 mV and the disconnection detection current is 4 nA, the detection time is 0.5 s (seconds). To shorten this,
Just increase the disconnection detection current, for example, increase the detection time to 5 m.
In order to set the disconnection detection current to 400n, which is 100 times
A, and it is necessary to turn on the analog switch 10 for 5ms or more to determine a disconnection.However, when the disconnection detection current is increased as described above, the error due to the voltage drop of the signal source resistance is held by the line capacitance. , it is necessary not to take temperature measurements until this is discharged by the signal source resistance. For this discharge time, for example, the line capacitance is 10'pF, the signal source resistance is 500Ω
Then, the time constant is 5 μs. The discharge time is from 200mV, which is the disconnection detection voltage, to 0, which is the minimum range of 2mV.
It is determined as the time required to discharge up to 2μ, which is 1%. If the discharge time is t, 2μV=200m
If the relationship of Vxe is established and the numerical value is substituted into the above formula, t is 5
It is determined as 7.5X10-6s. Therefore, if the temperature is measured after waiting for a discharge time that is 12 times the time constant or more, the error can be ignored.

Next, a second embodiment of the present invention will be described with reference to FIG.

This embodiment shows a disconnection detection circuit for an intelligent temperature measuring device that includes a microcomputer and performs linearization processing and the like. In FIG. 2, the same elements shown in FIG. 1 are given the same reference numerals. The elements indicated by numerals 1 to 11 and their connection structures are exactly the same as in the previous embodiment. A multiplexer 12 selects one of the output signals of the amplifier 8 for amplifying the temperature measurement signal and the amplifier 11 for amplifying the disconnection detection signal. 13 is an A/D converter, 14 is a digital signal processing unit including a microcomputer and peripheral circuits, and 15 is a D/A converter. Digital signal processing section 1
4 is a multiplexer 12 and an analog switch 9,1
1 to control their operations. 16 is an analog output terminal, and 17 is a communication terminal. The disconnection detection operation in this circuit is performed by appropriately controlling the on/off operations of the analog switches 9 and 10, and this is the same as that described in the previous embodiment. In this embodiment, the on/off operation of the analog switch 910 is configured to be controlled by the digital signal processing section 14.

In the disconnection detection operation by the disconnection detection circuit having the above configuration, the analog switch 10 is turned on by a digital control signal given from the digital signal processing section 14, waits for a disconnection detection time (for example, 5 m5), and then the multiplexer 12 selects the amplifier 11. switch to the side, A/D converter 13
The output signal of the amplifier 11 is inputted via. At this time, when the input signal is greater than a preset disconnection detection level, disconnection processing is performed, and when it is smaller than the input signal, the connection relationship of the circuit is switched and the process then proceeds to temperature measurement processing. When transitioning to temperature measurement processing, the analog switch 10 is first turned off using the same control signal from the digital signal processing section 14, and after waiting for the charge in the line capacitance of the input electrical wiring to be discharged, the analog switch 9 is turned on. At the same time, the multiplexer 12 switches to the amplifier 8 side, and the output signal is inputted via the A/D converter 13.

In the embodiment described above, it is possible to quickly inspect whether or not there is a disconnection state before the temperature is measured by the temperature measuring device, and to perform disconnection processing. In this embodiment, various output processes can be performed as necessary when detecting a disconnection. For example, you can immediately turn off the analog output in the event of a wire breakage, or set the analog output to 0■, or if you have a device with a communication function, you can suspend temperature measurement data and include a wire breakage alarm in the communication data. .

Another feature of the disconnection detection circuit according to the invention is that it can be applied to a multi-range type temperature measuring device. In other words, in the eight wire breakage detection circuits according to the present invention, the value of the current for wire breakage detection can be set to a large value, so there is no need to change the detection current even when the range changes, and wire breakage can be detected quickly and accurately. It can be carried out.

FIG. 3 shows an example of a circuit according to a third embodiment of the present invention.

This embodiment has a configuration in which the amplifier 11 for amplifying the disconnection detection signal is replaced with a comparator 18 in the configuration of the second embodiment. The operation is basically the same as that of the disconnection detection circuit of the second embodiment. The output of the comparator 18 is configured to be directly input to the digital signal processing unit 14, so the multiplexer 12 is no longer necessary. In the disconnection detection circuit according to the present invention, as described above, the disconnection detection circuit 8
Since a large current can be taken, it becomes possible to detect a wire breakage using the comparator 18 as in this embodiment. Further, since the output of the comparator 18 may be "H" or "L", the A/D converter 13 is not necessary for the output of the comparator 18. According to this configuration, the hardware and software can be configured more easily. Furthermore, in a field-installed temperature measuring device in which the electrical wiring is short and the line capacitance is small, the analog switch 10 can be omitted, and the circuit configuration is further simplified.

Next, based on FIG. 4, the fourth circuit of the eight disconnection detection circuits according to the present invention
An example will be explained. This embodiment shows an example in which a disconnection detection circuit according to the present invention is applied to a temperature measuring device configured for multi-point measurement. In this example, the fourth
As shown in the figure, it has n thermocouples 1(1) to 1(n). Therefore, there are n pairs of input terminals 2.3 corresponding to each of the n thermocouples. In the figure, (n) indicates a channel. MPX is a channel selection multiplexer, and n multiplexers are provided corresponding to each thermocouple. In multi-point measurements, each thermocouple generates 8 different thermoelectromotive forces, so insulation between channels is required, so a double-ended multiplexer MP is required.
X (1) to MPX (n) are provided. The circuit configuration after each multiplexer is, for example, the same as the circuit configuration shown in FIG. However, the multiplexer drive signal S corresponding to each channel is sent from the digital signal processing unit 14.

The difference is that the configuration in which ~S7 is output and the D/A converter 15 has a multi-point converter configuration.

According to the configuration of the above embodiment, even if the temperature measurement range is changed, disconnection can be detected quickly and reliably without changing the circuit. The configuration of the disconnection detection circuit according to the present invention is particularly effective when applied to a multi-point, multi-range type temperature measuring device.

Further, when the disconnection detection circuit according to the present invention is applied to a multi-point temperature measuring device, two operating methods can be considered.

The first operation method is a method in which the same operation as in the embodiments of FIGS. 2 and 3 is performed for each channel. In the case of this operation method, first, a disconnection of the first channel is detected,
Next, temperature measurement is performed, then digital processing such as linearization processing is performed, and finally, the operation is moved to the next channel. In this operating method, it is also possible to configure the next channel to detect disconnection during digital signal processing. This enables disconnection detection and high-speed processing. The second operating method is an operating method in which disconnection of all channels is detected before temperature measurement.

This operating method has the advantage that the actually connected channels and disconnected channels are known in advance, so temperature measurements of unnecessary channels can be omitted, and the processing by the microcomputer is reduced. , the load can be reduced.

In each of the above embodiments, only the case where a thermocouple is used as the temperature detection element has been explained, but the disconnection detection circuit according to the present invention can also be applied to a temperature measurement device configured to input an output signal of a resistance temperature detector. can do. FIG. 5 shows a fifth embodiment, which is an example of this application.

In Fig. 5, 21 is a resistance temperature sensor, and the temperature is 2°3.3.
' is an input terminal, 4.4' is a resistor, 5.5' is a capacitor, 8 and 22 are amplifiers, 23 is a multiplexer for selecting the output of the amplifiers 8 and 22, and 24 is a power supply for the resistance temperature detector. The other configurations are the same as those described in the previous embodiment, and the same elements are given the same reference numerals and their explanations will be omitted. Next, the temperature measurement principle of the circuit according to this embodiment will be explained.

As shown in FIG. 5, a driving current I is applied to the resistance temperature sensor 21. is applied, the analog switch 9 is turned on, and the analog switch 10 is turned off, so that the output voltage el+ of the amplifiers 22 and 8 is
62, el = CHX (RO+Rt +
2 ro ) X l0e2 =G+ X ro
It becomes 1°. Here, Ro is the resistance value of the resistance temperature detector at 0°C, R1 is the change in resistance due to temperature change, ro is the wiring resistance, and G is the gain of the amplifiers 8 and 22. This is simplified for convenience of explanation. Therefore, they were assumed to be equal. Temperature data is obtained by extracting the term R1 from el+e2. Therefore, when e and -e2 are calculated, e+ 62=G+ X (Ro +R+)X
I.

=CHXRo X 10 +GI XRI X 1
It becomes 0. Here G1. Since RO and IO are known,
It can be erased by preparing it in advance as data for the digital signal processing section 14, and as a result, G, xR, xio, which is proportional to R, can be obtained.

In a temperature measuring device that uses a resistance temperature detector having the above configuration as a temperature detection element, it is a three-wire type resistance temperature detector input circuit, so it is necessary to check for disconnections at three locations. First, when the wire connected to the input terminal 2 is disconnected, the capacitor 5' receives a constant current I. Since the battery is rapidly charged and el is completely blown out, a disconnection can be detected by measuring e. Next, when the line connected to the input terminal 3' is disconnected, the disconnection detection circuit described in each of the above embodiments detects the disconnection. Finally, when the line connected to the input terminal 3 is disconnected, the capacitors 5 and 5' are both rapidly charged by the constant current of 1 DEG from the power sources 2 and 4, so that the disconnection can be easily detected.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, in a temperature measuring device having at least one temperature detection element such as a thermocouple, the input filter circuit is disconnected to detect disconnection. Disconnection can be detected quickly and accurately, and can be detected safely without disturbing the process. In addition, it has a configuration suitable for a multi-point temperature measurement device having multiple temperature detection elements, and even if the input range is changed, disconnection can be detected quickly and reliably without changing the circuit constants. It is easy to apply to multi-range type temperature measuring devices,
A multi-point input type temperature measuring device can be easily configured. In addition, when the disconnection detection circuit section is configured using a comparator, the fact of the presence or absence of a disconnection can be directly input to the signal processing section, which simplifies the configuration of the signal processing section and improves processing speed. can be done.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a first embodiment of an eight disconnection detection circuit according to the present invention, Fig. 2 is a circuit diagram showing a second embodiment of the same circuit, and Fig. 3 is a circuit diagram showing a third embodiment of the same circuit. 4 is a circuit diagram showing a fourth embodiment of the same circuit, FIG. 5 is a circuit diagram showing a fifth embodiment of the same circuit, and FIG. 6 is a circuit diagram of a conventional disconnection detection circuit. . [Explanation of symbols] 1e・Conflictee 2.3... 4・・・・ 5・・-ee 6・Kite... 7... 8◆・---・Ku 9.10... 11 -・φ- 12-... 13...Yanagi 14...- 18...

Claims (6)

[Claims] (1) at least one temperature detection element, a filter circuit that removes noise from the output signal of the temperature detection element, and a first amplifier that amplifies the output signal of the filter circuit;
In the temperature measuring device configured to extract temperature information based on the output signal of the first amplifier, a switch means provided between the temperature detection element and the filter circuit, and a disconnection detection device in the temperature detection element. and a second amplifier connected to a terminal of the temperature detection element, and when detecting a wire breakage, turns off the switch means and detects a wire breakage state using the output of the second amplifier. A disconnection detection circuit for a temperature measuring device, characterized in that: (2) A disconnection detection circuit for a temperature measuring device according to claim 1, including a multiplexer that selects and takes in the output signals of the first and second amplifiers, and an A/D converter that digitizes the output signal of the multiplexer. and a digital signal processing means for inputting the output signal of the A/D converter to perform signal processing for temperature measurement or disconnection detection, and controlling the operation of the switch means and the multiplexer; A disconnection detection circuit for a temperature measuring device, characterized in that temperature measurement processing and disconnection detection processing are selectively performed. (3) at least one temperature detection element, a filter circuit that removes noise from the output signal of the temperature detection element, an amplifier that amplifies the output signal of the filter circuit, and an amplifier that amplifies temperature information based on the output signal of the amplifier. In a temperature measuring device configured to be taken out, a switch means provided between the temperature detection element and the filter circuit, a power supply circuit that supplies a disconnection detection current to the temperature detection element, and the temperature detection element A disconnection detection circuit for a temperature measuring device, comprising a comparator connected to a terminal of the temperature measuring device, wherein when a disconnection is detected, the switch means is turned off, and the disconnection state is detected by the output of the comparator. (4) In the disconnection detection circuit of the temperature measuring device according to claim 1, an A/D that digitizes the output signal of the amplifier.
a converter, and digital signal processing means for inputting the output signal of the A/D converter and the output signal of the comparator to perform signal processing for temperature measurement or disconnection detection, and for controlling the operation of the switch means, A disconnection detection circuit for a temperature measuring device, characterized in that the digital signal processing means selectively performs temperature measurement processing and disconnection detection processing. (5) A disconnection detection circuit for a temperature measuring device according to claim 2 or 4, which has a plurality of temperature detection elements, and a connection switching means is provided at a terminal portion of each temperature detection element, and the digital signal processing means A disconnection detection circuit for a temperature measuring device, characterized in that a switching operation of a connection switching means is controlled to select and take in an output signal of the temperature detection element. (6) In the temperature detection circuit of the temperature measuring device according to any one of claims 1 to 5, another switch means is provided between the terminal of the temperature detection element and the output terminal of the power supply circuit, and the output terminal of the power supply circuit is provided with another switch means. A disconnection detection circuit for a temperature measuring device, characterized in that the input terminal of the second amplifier or comparator is connected.