JP2985131B1 - Thermistor monitoring device - Google Patents

Abstract

An abnormal state caused by disconnection or short circuit of a thermistor, a control signal not properly output from a monitoring control unit, and information from a thermistor not being input to the monitoring control unit is detected. Increase the reliability of thermistor monitoring. SOLUTION: A voltage between both ends of the thermistor 3 detected in a high temperature region detection state in which a combined resistance value of a first pull-up resistor 2a and a second pull-up resistor 2b connected in parallel is set as a pull-up resistance value of the thermistor 3 is A / D. The A / D value 1 obtained by A / D conversion by the conversion means 8 and the voltage between both ends of the thermistor 3 detected in the low temperature region detection state in which the resistance value of the first pull-up resistor 2a is set as the pull-up resistance value of the thermistor 3 are A / D. When the A / D difference, which is the difference from the A / D value 2 that has been A / D converted by the D conversion means 8, is smaller than the abnormality determination value X1, the abnormal state determination means 10 determines that the state is abnormal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermistor monitoring device for monitoring the temperature of a thermistor by detecting a voltage between both ends of the thermistor whose resistance value changes with a change in temperature.

[0002]

2. Description of the Related Art Conventionally, a thermistor (Thermistor: Thermally Sensitive) which is a heat-sensitive resistor is conventionally used.
Resitor) is used as a warming element for monitoring the temperature of hot water and the temperature of a heater in an automatic water heater. Note that an NTC thermistor having a negative temperature coefficient is generally called a thermistor.

As a method of monitoring the temperature using a thermistor, one side of the thermistor is connected to the ground and the other side is connected to a power supply via a pull-up resistor, and the voltage between both ends of the thermistor is monitored by a monitoring device composed of a microcomputer or the like. Is common,
A monitoring device that detects a change in resistance of the thermistor due to a change in temperature as a change in voltage obtains the temperature of the thermistor corresponding to the voltage across the monitor.

Since the thermistor having a negative temperature coefficient has a property that the resistance value is large in a low temperature region and is small in a high temperature region, the resistance value of a pull-up resistor is large in a low temperature region. Since reducing the resistance value of the pull-up resistor in the high-temperature region has a significant effect on improving monitoring accuracy, a thermistor monitoring device that can change the resistance value of the pull-up resistor between the low-temperature region and the high-temperature region has also been proposed. ing.

FIG. 3 shows a schematic configuration of a conventional pull-up resistor variable type thermistor monitoring device 30 as described above, in which a first pull-up resistor 31 and a second pull-up resistor 32 connected in parallel are connected. Is supplied from the DC power supply 34 to the thermistor 33, and the non-earth side of the thermistor 33 is input to the input port P1 of the monitor control unit 35, so that the non-earth side potential of the thermistor 33 can be detected by the monitor control unit 35. ing.

[0006] An on / off signal for switching the pull-up resistor is output from an output port P0 of the monitoring control unit 35, and this signal is input to the base of a switching element 36 composed of an NPN digital transistor or the like. Is done. That is, since the second pull-up resistor 32 is connected in parallel with the first pull-up resistor 31 via the switching element 36, when the output port P0 of the monitoring control unit 35 is off, the second pull-up resistor 32 is connected. 32, the resistance value of the first pull-up resistor 31 becomes the pull-up resistance value of the thermistor 33, and when the output port P0 of the monitoring control unit 35 is on, the first pull-up resistor 31 and the second pull-up resistor are connected. The resistance value in parallel with the resistor 32 is thermistor 3
The pull-up resistance value is 3.

Therefore, in a low temperature region where a higher pull-up resistance value is desirable, the output value of the first pull-up resistor 31 is turned off by turning off the output port P0 of the monitor control unit 35. In a high-temperature region where a lower pull-up resistance value is desirable, the monitoring controller 35
, The combined resistance value of the first pull-up resistor 31 and the second pull-up resistor 32 can be used as the pull-up resistance value of the thermistor 33. As described above, by selecting an appropriate pull-up resistance value according to the measurement temperature region, highly accurate monitoring can be performed in both the low temperature region and the high temperature region.

The monitoring controller 35 can be made using a one-chip microcomputer or the like, and stores a control program, control data, and the like in a ROM in accordance with the basic characteristics of the thermistor 33, the detected temperature range, and the like. You should let it. At this time, when an 8-bit CPU is used for the monitoring control unit 35, when the voltage between both ends of the thermistor 33 input from the input port P1 of the monitoring control unit 35 is A / D converted and quantized, the resolution is 2 ⁸ = 256, "0" ~
The range is “255”. Therefore, these "0" to "25"
By allocating the 5 ″ range to the temperature range (voltage value due to resistance change) that can be detected by the thermistor 33,
The A / D value obtained by converting the voltage between the terminals 3 and the temperature information is associated with each other, and the temperature detected by the thermistor 33 can be determined.

[0009]

However, in the thermistor monitoring device in which the monitoring control section is constituted by the microcomputer or the like as described above, if the detected temperature of the thermistor is out of the monitoring range, it can be determined that there is an abnormality. If the thermistor is disconnected or short-circuited (when the detection voltage of the monitoring control unit is at the same level as the power supply potential or the ground potential), it may be mistaken as the lowest or highest detectable temperature. I am worried about the certainty of the judgment.

[0010] The reason is that, in general, an error occurs in the detection level in the microcomputer as the monitoring control unit, and in the 8-bit microcomputer, an error of about 3 is mixed in the A / D value. A / D value 2 for detection
If the short-circuit detection of the thermistor is set near the A / D value 0 near 55, an erroneous detection will occur due to a reading error of the microcomputer.

Incidentally, in order to prevent such erroneous detection, the disconnection detection level of the thermistor is lowered below the low level of the monitorable temperature range, or the thermistor of the thermistor is lower than the high level of the monitorable temperature range. It is necessary to increase the short-circuit detection level, and consequently, to narrow the monitorable temperature range of the thermistor.

In addition, in the thermistor monitoring apparatus having the above-described conventional configuration, the output port used for variable control of the pull-up resistance value and the input port used for detecting the voltage of the thermistor are open due to disconnection or the like. There is no way to detect this.

[0013]

In order to solve the above-mentioned problems, a thermistor monitoring device according to a first aspect detects a voltage between both ends of a thermistor whose resistance value changes with a temperature change, and detects the temperature of the thermistor. In the thermistor monitoring device (1) to be monitored, a pull-up resistor (for example, a first pull-up resistor 2a and a second pull-up resistor 2b) having a resistance value suitable for temperature detection in a high-temperature region generated depending on the element characteristics of the thermistor. Are connected to the thermistor in a high-temperature region detection state, and a low-temperature region in which a pull-up resistor (for example, a first pull-up resistor 2a) having a resistance value suitable for temperature detection in a low-temperature region is connected to the thermistor. A detection state switching means (for example,
The switch element 6 and the pull-up resistance switching control means 7) of the monitoring control unit 5; and both ends of the thermistor measured in the high-temperature area detection state and the low-temperature area detection state within a short time in which the temperature change of the thermistor can be ignored. When the voltage difference is smaller than an abnormality determination value determined in advance based on the element characteristics of the thermistor, an abnormal state determination means (10) for determining that the temperature is not normally detected by the thermistor; , Was provided.

Therefore, in the thermistor monitoring device according to the first aspect, when a short circuit or disconnection of the thermistor occurs, the detection voltage in the high temperature region detection state and the detection voltage in the low temperature region detection state are substantially at the same level. As a result, the difference between the two detection voltages becomes extremely small, so that a case where this voltage difference is smaller than a predetermined abnormality determination value can be determined as an abnormal state.

In addition, the detection state switching means does not properly switch the pull-up resistance, so that the high temperature area detection state and the low temperature area detection state are measured with the same resistance value, or the detection signal path of the voltage across the thermistor is disconnected. Even when the voltage across the thermistor is not properly input to the abnormal state determination means, for example, the detection voltage in the high-temperature region detection state and the detection voltage in the low-temperature region detection state are almost the same level, A case where the difference between the detected voltages is extremely small and the voltage difference is smaller than a predetermined abnormality determination value can be determined as an abnormal state.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a thermistor monitoring apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a schematic configuration of a thermistor monitoring device 1, in which a first pull-up resistor 2a and a second pull-up resistor 2a are connected in parallel.
DC power supply 4 is connected to thermistor 3 via pull-up resistor 2b.
And the non-ground side of the thermistor 3 is input to the input port P1 of the monitoring control unit 5, and the thermistor 3
Can be detected by the monitoring control unit 5.

An on / off signal for pull-up resistor switching is output from an output port P0 of the monitoring control unit 5, and this signal is input to the base of a switching element 6 composed of an NPN digital transistor or the like. Is done.
That is, since the second pull-up resistor 2b is connected in parallel with the first pull-up resistor 2a via the switching element 6, when the output port P0 of the monitoring control unit 5 is off, the second pull-up resistor 2b is connected. Since the current is not supplied to the second pull-up resistor 2a, the resistance value of the first pull-up resistor 2a becomes the pull-up resistance value of the thermistor 3, and when the output port P0 of the monitoring control unit 5 is on, the first pull-up resistor 2a and the second pull-up resistor The resistance in parallel with the resistor 2b becomes the pull-up resistance of the thermistor 3.

Therefore, in a low temperature region where a higher pull-up resistance value is desirable, the pull-up resistance switching control means 7 of the monitoring control unit 5 turns off the output port P0, thereby causing the first output port P0 to turn off.
The resistance value of the pull-up resistor 2a is used as the pull-up resistance value of the thermistor 3, and in a high temperature region where a lower pull-up resistance value is desirable, the pull-up resistance switching control means 7 of the monitoring controller 5 turns on the output port P0. Thus, the combined resistance value of the first pull-up resistor 2a and the second pull-up resistor 2b can be used as the pull-up resistance value of the thermistor 3.

That is, in the present embodiment, the pull-up resistance switching control means 7 and the switching element 6 cooperate to provide a "resistance suitable for temperature detection in a high-temperature region generated depending on the element characteristics of the thermistor 3". A high-temperature region detection state in which a pull-up resistor of a value (a combined resistance in which the first pull-up resistor 2a and the second pull-up resistor 2 are connected in parallel) to the thermistor 3 and a resistance value suitable for temperature detection in a low-temperature region It functions as "detection state switching means capable of controlling switching between a low-temperature region detection state in which a pull-up resistor (first pull-up resistor 2a) is connected to the thermistor 3".

The voltage across the thermistor 3 input from the input port P1 of the monitoring control unit 5 is converted to digital data by the A / D conversion unit 8 of the monitoring control unit 5 and then sent to the thermistor temperature determination unit 9. The thermistor temperature determination means 9 determines the detected temperature. In this embodiment, the resolution of the A / D conversion means 8 is set to 2 ⁸ = 256.
And the temperature detection range by the thermistor 3 (for example, 30
The temperature of the thermistor 3 is determined based on the detected A / D value by the thermistor temperature determination means 9 in which a correspondence table between the A / D values “0” to “255” is stored in advance. It is.

In the thermistor monitoring apparatus 1 of the present embodiment shown in FIG. 1, the temperature of the thermistor 3 determined by the thermistor temperature determining means 9 can be taken out as a temperature signal from the output port P2 of the monitoring control unit 5. The temperature signal is used for controlling the temperature of a device with a built-in thermistor (such as an instantaneous water heater) or for reporting temperature information. Further, instead of installing the thermistor monitoring device as an independent device in the device with a built-in thermistor, various functions of the thermistor monitoring device may be included in the control function of the device with a built-in thermistor.

The temperature detection by the thermistor 3 differs between the high-temperature region detection state and the low-temperature region detection state in which the pull-up resistance value is varied by the pull-up resistance switching control means 7 and the switching element 6, respectively.
A value characteristic curve is obtained, and this characteristic is shown in FIG.

That is, the A / D value of the A / D value 1 obtained by A / D converting the voltage between both ends of the thermistor 3 detected with a low pull-up resistance value (parallel resistance value of the first pull-up resistance 2a and the second pull-up resistance 2b). The characteristic curve has a steep slope in the high-temperature region, and the amount of increase in the A / D value with respect to the temperature change is large, so that highly accurate temperature detection can be performed in the high-temperature region. The characteristic curve of the A / D value 2 obtained by A / D converting the voltage between both ends of the thermistor 3 detected by the value (the resistance value of only the first pull-up resistor 2a) has a steep slope in a low temperature region, and the temperature changes. , The amount of decrease in the A / D value is large, so that highly accurate temperature detection can be performed in a low temperature region.

The switching control of the pull-up resistor by the on / off signal from the pull-up resistor switching control means 7 is performed, for example, when the temperature judgment by the thermistor temperature judgment means 9 reaches a predetermined temperature. The pull-up resistance switching control means 7 instructs the pull-up resistance switching control means 7 to switch the pull-up resistance on the basis of the pull-up resistance value. On the other hand, when determining the temperature based on the A / D value input from the A / D conversion means 8, the thermistor temperature determination means 9 performs the switching-controlled characteristic curve (A / D value 1).
Alternatively, an appropriate temperature value of the thermistor 3 may be determined in association with one of the A / D values 2).

In FIG. 2, an A / D value 1 obtained by measuring the entire measured temperature range in the high temperature region detection state and an A / D value 2 obtained by measuring the entire measured temperature range in the low temperature region detection state are shown.
Also, an A / D difference characteristic curve which is a difference from the above is shown. In the characteristic curve of the A / D difference shown in FIG. 2, if the value at the lowest temperature 30 ° C. measurable by the thermistor 3 is X1, and the value at the highest temperature 310 ° C. measurable by the thermistor 3 is X2, the thermistor 3 In the characteristics of A, the A / D difference is always X1 in the temperature measurement range (30 ° C. to 310 ° C.) when X2 ≧ X1.
From the above, it can be determined that an A / D difference lower than X1 is an abnormal state.

In this embodiment, the monitoring control section 5 is provided with an abnormal state determining means 10 in order to determine the above measurement abnormality. That is, the abnormal state determination means 10 determines the difference (A / D) between the voltages across the thermistor 3 measured in the high-temperature region detection state and the low-temperature region detection state within a short period of time such that the temperature change of the thermistor 3 can be ignored.
If the difference is smaller than the abnormality determination value X1 determined in advance based on the element characteristics of the thermistor 3, it is determined that the temperature is not abnormally detected by the thermistor 3 in an abnormal state.

The abnormal states which can be determined by the abnormal state determining means 10 are a state in which the thermistor 3 is disconnected or short-circuited and a state in which the output port P0 and the input port P1 of the monitoring control unit 5 are open.

That is, when the thermistor 3 is disconnected, the voltage input from the input port P1 is substantially equal to the voltage of the DC power supply 4 in both the high-temperature region detection state and the low-temperature region detection state. It is determined that the A / D difference between the D value 1 and the A / D value 2 is close to 0, which satisfies the condition that the A / D difference is smaller than X1, and that the thermistor 3 does not perform normal temperature detection. Is appropriate.

When the thermistor 3 is in a short-circuit state, the voltage input from the input port P1 is substantially equal to the ground potential in both the high-temperature region detection state and the low-temperature region detection state. A / D of A / D value 2
It is appropriate to determine that the D difference is close to 0 and the condition that the difference is smaller than X1 is satisfied, and that the thermistor 3 is in an abnormal state in which normal temperature detection is not performed.

Similarly, when the output port P0 of the monitoring control unit 5 is in the open state and the switching control of the switching element 6 is not properly performed, the switching control between the high temperature region detection state and the low temperature region detection state is performed. Since it is not performed properly, it is fixed to the pull-up resistance value of only the first pull-up resistor 2a, and the A / D value 2 is input as the A / D value 1 from the input port P1, so that the actual measurement is performed. The A / D difference between the A / D value 1 and the A / D value 2 is close to 0, which satisfies the condition that the A / D value is smaller than X1 and the thermistor 3 does not perform normal temperature detection. It is appropriate to judge.

When the input port P1 of the monitoring control unit 5 is in the open state and the voltage across the thermistor 3 is not properly input, the potential level is the same in both the high-temperature region detection state and the low-temperature region detection state, and is measured. A / D value 1 and A / D
It is appropriate to determine that the A / D difference from the value 2 is close to 0, smaller than X1, and that the condition that the thermistor 3 does not perform normal temperature detection is abnormal.

The abnormal state judging means 10 in this embodiment receives the supply of the A / D difference every time the thermistor temperature judging means 9 judges the temperature.
It is determined whether the difference is smaller than X1, which is an abnormality determination value, and an abnormal state detection signal is output from the output port P3 only when it is determined that the state is abnormal.
When the control function unit of the thermistor built-in device receives the abnormal state detection signal from the thermistor monitoring device 1, it performs appropriate processing such as notification of occurrence of an abnormality and operation restriction control.

Further, the abnormal condition judging means 10 is not limited to detecting the condition each time the temperature is judged by the thermistor temperature judging device 9, but may perform the abnormal judging operation at its own timing. Only at the time of the determination, the A / D conversion unit 8 directly executes the switching operation of the pull-up resistor by the pull-up resistor switching control unit 7 or receives the A / D value 1 and the A / D value 2 directly from the A / D conversion unit 8 to perform the A / D conversion. A configuration in which the difference is calculated and the abnormality is determined may be employed. In order to
How the abnormal state determination means obtains the difference between the voltages across the thermistor 3 measured in the high temperature region detection state and the low temperature region detection state, which are necessary for performing the abnormality state determination, is particularly limited. Not something.

[0035]

As described above, according to the thermistor monitoring device according to the first aspect, when the thermistor is short-circuited or disconnected, the detection state switching means does not properly switch the pull-up resistance. When the high-temperature area detection state and the low-temperature area detection state are measured with the same resistance value, or the voltage across the thermistor is not properly input to the abnormal state determination means because the detection signal path for the voltage across the thermistor is broken. Since the detection voltage in the high-temperature region detection state and the detection voltage in the low-temperature region detection state are almost the same level, the difference between the two detection voltages becomes extremely small. A small case can be determined as an abnormal state, and the reliability of the thermistor monitoring device becomes extremely high.

[Brief description of the drawings]

FIG. 1 is a schematic functional block diagram of a thermistor monitoring device according to a first embodiment.

FIG. 2 High temperature region detection state (pull-up resistance value is low)
, A / D value 2 in the low-temperature region detection state (high pull-up resistance value), A / D value 1 and A / D value 2
FIG. 4 is a characteristic diagram showing respective characteristic curves of an A / D difference which is a difference between.

FIG. 3 is a schematic functional block diagram of a conventional thermistor monitoring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermistor monitoring device 2a 1st pull-up resistor 2b 2nd pull-up resistor 5 Monitoring control part 6 Switch element 7 Pull-up resistance switching control means 10 Abnormal state determination means

Claims (1)

(57) [Claims] 1. A thermistor monitoring device for monitoring a temperature of a thermistor by detecting a voltage between both ends of the thermistor whose resistance value changes with a temperature change, wherein a temperature of a high-temperature region generated depending on element characteristics of the thermistor is detected. Detection that can be controlled to switch between a high-temperature region detection state in which a pull-up resistor with an appropriate resistance value is connected to the thermistor and a low-temperature region detection state in which a pull-up resistor with a resistance value suitable for low-temperature region is connected to the thermistor. The state switching means, and the difference between the voltages at both ends of the thermistor measured in the high-temperature region detection state and the low-temperature region detection state within a short time in which the temperature change of the thermistor can be ignored is predetermined based on the element characteristics of the thermistor. Abnormal state determination that determines that the temperature is not normal by the thermistor when the temperature is smaller than the abnormal determination value Thermistor monitoring apparatus being characterized in that it is assumed that comprises a stage, a.