Pressure measuring device and control method for pressure measuring device

Abstract

To improve the safety of a pressure measuring device.SOLUTION: A heater 12 heats a pressure sensor 11. A heater temperature sensor 14 measures the temperature of the heater 12. A pressure receiving part temperature sensor 15 measures the temperature of the pressure sensor 11. A control circuit 21 controls the heating performed by the heater 12 based on the temperature of the pressure sensor 11 measured by the pressure receiving part temperature sensor 15. A heater temperature limit circuit 23 cuts off a driving current of the heater 12 based on the temperature of the heater 12 measured by the heater temperature sensor 14. An abnormality detection unit 20 causes the heater temperature limit circuit 23 to perform an operation when the temperature of the heater 12 is a predetermined temperature to detect an abnormality in the heater temperature limit circuit 23, and when detecting an abnormality, notifies an alarm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a pressure measurement device that prevents overheating by detecting an abnormality in a heater temperature limit circuit in a capacitance-type sensor, and a control method for the pressure measurement device.

Background Art

[0002] In semiconductor manufacturing equipment, diaphragm vacuum gauges having pressure sensors are often used as pressure measurement devices. When the gas used in the semiconductor manufacturing process adheres to the pressure sensor, the characteristics of the diaphragm vacuum gauge change. Therefore, some diaphragm vacuum gauges used in semiconductor manufacturing equipment have a heater built therein for heating the pressure sensor, and there are models that make it difficult for the gas to adhere due to the temperature rise by the heater. The heater is controlled by a heater control unit provided in the diaphragm vacuum gauge, and by generating heat and heating the inside of the pressure sensor, the temperature around the diaphragm inside the pressure sensor is maintained at a high temperature where contaminants do not deposit.

[0003] However, in a diaphragm vacuum gauge with a heater, there is a risk of accidents such as fires due to overheating by the heater. Therefore, conventionally, a diaphragm vacuum gauge with a heater having a function of controlling overheating of the heater has been proposed. For example, in a diaphragm vacuum gauge that controls the on / off of the heater current with a signal from a CPU (Central Processing Unit), even if the CPU malfunctions and it becomes difficult to control the heater current, a heater temperature limit circuit that detects overheating by the heater and cuts off the current has been proposed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, with conventional methods, if the heater temperature limit circuit itself fails, the user may continue to use the diaphragm vacuum gauge without realizing the malfunction. In this state, if the CPU malfunctions, it becomes difficult to control the current of the heater temperature limit circuit. In that case, the current to the heater will not be cut off, and there is a risk of fire due to the heater overheating.

[0006] This invention aims to solve these problems and improve the safety of pressure measuring devices. [Means for solving the problem]

[0007] The pressure measuring device according to the present invention comprises a pressure sensor, a heater for heating the pressure sensor, a heater temperature sensor for measuring the temperature of the heater, a pressure receiving temperature sensor for measuring the temperature of the pressure sensor, and a control circuit for controlling heating by the heater based on the temperature of the pressure sensor measured by the pressure receiving temperature sensor. When a voltage corresponding to the temperature of the heater is applied, A heater temperature limit circuit that cuts off the drive current of the heater based on the heater temperature measured by the heater temperature sensor, The heater temperature limit circuit has a dummy resistor that applies a predetermined voltage corresponding to the heater temperature when the heater temperature reaches a predetermined temperature, and the dummy resistor is connected to the heater temperature limit circuit. The temperature of the heater is The aforementioned The system includes an abnormality detection unit that causes the heater temperature limit circuit to perform an operation at a predetermined temperature, detects an abnormality in the heater temperature limit circuit, and issues an alarm when an abnormality is detected.

[0008] In the above-described pressure measuring device, the heater temperature limit circuit interrupts the heater drive current based on the heater temperature when a voltage corresponding to the heater temperature is applied, and the abnormality detection unit has a dummy resistor that applies a predetermined voltage corresponding to the predetermined temperature to the heater temperature limit circuit, and by connecting the dummy resistor to the heater temperature limit circuit, an abnormality in the heater temperature limit circuit at the predetermined temperature may be detected.

[0009] In the above-described pressure measuring device, the abnormality detection unit may have a first dummy resistor and a second dummy resistor with different resistance values ​​as the dummy resistors, and by switching between the first dummy resistor and the second dummy resistor and connecting them to the heater temperature limit circuit, an abnormality in the heater temperature limit circuit may be detected based on the operation of the heater temperature limit circuit when different voltages are applied to the heater temperature limit circuit.

[0010] In the above-described pressure measuring device, the heater temperature limit circuit cuts off the heater drive current when the heater temperature reaches a predetermined limit temperature, and the abnormality detection unit may connect the first dummy resistor to the heater temperature limit circuit to detect an abnormality in the heater temperature limit circuit when the predetermined temperature is higher than the limit temperature, and connect the second dummy resistor to the heater temperature limit circuit to detect an abnormality in the heater temperature limit circuit when the predetermined temperature is lower than the limit temperature.

[0011] In the above-described pressure measuring device, the heater temperature limit circuit may interrupt the heater drive current based on the heater temperature by applying a voltage corresponding to the heater temperature, and the abnormality detection unit may detect an abnormality in the heater temperature limit circuit at the predetermined temperature by applying a predetermined voltage corresponding to the predetermined temperature to the heater temperature limit circuit.

[0012] The control method for a pressure measuring device according to the present invention comprises a pressure sensor, a heater for heating the pressure sensor, a heater temperature sensor for measuring the temperature of the heater, a pressure receiving temperature sensor for measuring the temperature of the pressure sensor, a control circuit for controlling heating by the heater based on the temperature of the pressure sensor measured by the pressure receiving temperature sensor, and a heater temperature limit circuit for interrupting the drive current of the heater based on the temperature of the heater measured by the heater temperature sensor. The control method causes the heater temperature limit circuit to perform an operation when the temperature of the heater is at a predetermined temperature, detects an abnormality in the heater temperature limit circuit, and issues an alarm when the abnormality is detected. [Effects of the Invention]

[0013] According to the pressure measuring device and control method described above, a predetermined voltage is applied to the heater temperature limit circuit, and an abnormality in the heater temperature limit circuit is detected based on its operation at that time. If an abnormality is detected, an alarm is sounded. In this way, the pressure measuring device can avoid accidents that would occur if the control circuit malfunctioned while the heater temperature limit circuit was still in use. As a result, the safety of the pressure measuring device can be improved. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a block diagram of a pressure measuring device according to the first embodiment. [Figure 2A] Figure 2A shows the relationship between thermistor characteristics and dummy resistance when an NTC thermistor is used as a heater temperature sensor. [Figure 2B] Figure 2B shows the relationship between the characteristics of a resistance thermometer and the dummy resistance value when the resistance thermometer is used as a heater temperature sensor. [Figure 3A] Figure 3A shows the relationship between the measured temperature and the corresponding dummy resistance value when an NTC thermistor is used as a heater temperature sensor. [Figure 3B] Figure 3B shows the relationship between the measured temperature and the corresponding dummy resistance value when a resistance thermometer is used as a heater temperature sensor. [Figure 4A] Figure 4A is a diagram summarizing the correspondence between faulty components and current interruption methods when using a thermistor. [Figure 4B] Figure 4B is a diagram summarizing the correspondence between faulty components and current interruption methods when using a thermistor. [Figure 4C] Figure 4C is a diagram summarizing the correspondence between faulty components and current interruption methods when using a thermistor. [Figure 4D] Figure 4D is a diagram summarizing the correspondence between faulty components and current interruption methods when using a thermistor. [Figure 5A] FIG. 5A is a diagram summarizing the correspondence between faulty components during the use of a resistance temperature detector and the current cutoff method. [Figure 5B] FIG. 5B is a diagram summarizing the correspondence between faulty components during the use of a resistance temperature detector and the current cutoff method. [Figure 5C] FIG. 5C is a diagram summarizing the correspondence between faulty components during the use of a resistance temperature detector and the current cutoff method. [Figure 5D] FIG. 5D is a diagram summarizing the correspondence between faulty components during the use of a resistance temperature detector and the current cutoff method. <00​​​​​​​​​​​​​​​​​​​​​​​​​​​Figure 1 is a block diagram of a pressure measuring device according to the first embodiment. The pressure measuring device 10 is, for example, a diaphragm vacuum gauge. The pressure measuring device 10 detects a failure in the heater temperature limit circuit 23, which could not be detected in conventional devices. In this embodiment, the pressure measuring device 10 connects a low-temperature dummy resistor 103 corresponding to a temperature lower than the limit temperature and a high-temperature dummy resistor 104 corresponding to a temperature higher than the limit temperature in parallel with the heater temperature sensor 14.

[0017] As an example, when an NTC thermistor is used as a heater temperature sensor 14, the relationship between the thermistor characteristics and the low-temperature dummy resistors 103 and 104 is illustrated in Figure 2A. Figure 2A is a diagram showing the relationship between thermistor characteristics and dummy resistance values ​​when an NTC thermistor is used as a heater temperature sensor. In the graph of Figure 2A, the horizontal axis represents temperature and the vertical axis represents resistance. The limit temperature in Figure 2A is the threshold temperature at which the heater temperature limit circuit 23 cuts off the current to the heater 12. The low-temperature dummy resistor 103 has a resistance value corresponding to the low-temperature abnormality detection temperature, which is lower than the limit temperature. The high-temperature dummy resistor 104 has a resistance value corresponding to the high-temperature abnormality detection temperature, which is higher than the limit temperature.

[0018] Furthermore, when a resistance thermometer is used as the heater temperature sensor 14, the relationship between the characteristics of the resistance thermometer and the low-temperature dummy resistors 103 and 104 is illustrated in Figure 2B. Figure 2B is a diagram showing the relationship between the characteristics of the resistance thermometer and the dummy resistance value when the resistance thermometer is used as the heater temperature sensor. In the graph of Figure 2B, the horizontal axis represents temperature and the vertical axis represents resistance. The limit temperature in Figure 2B is the threshold temperature at which the heater temperature limit circuit 23 cuts off the current to the heater 12. In this case as well, the low-temperature dummy resistor 103 has a resistance value corresponding to the low-temperature abnormality detection temperature, which is lower than the limit temperature. The high-temperature dummy resistor 104 has a resistance value corresponding to the high-temperature abnormality detection temperature, which is higher than the limit temperature.

[0019] Figure 3A shows the relationship between the measured temperature and the corresponding dummy resistance value when an NTC thermistor is used as a heater temperature sensor. Figure 3A shows an example where the limit temperature is 280°C. When an NTC thermistor is used as a heater temperature sensor, for example, the low-temperature side dummy resistance 103 is set to 29 (Ω) to correspond to the case where the measured temperature of the heater temperature sensor 14 is 270°C, which is the low-temperature side abnormal detection temperature. Similarly, the high-temperature side dummy resistance 104 is set to 22 (Ω) to correspond to the case where the measured temperature of the heater temperature sensor 14 is 290°C, which is the high-temperature side abnormal detection temperature. In particular, the limit temperature is set to 280°C here because if it is too high, it can cause a fire.

[0020] Figure 3B also shows the relationship between the measured temperature and the corresponding dummy resistance value when a resistance thermometer is used as a heater temperature sensor. Figure 3B also shows an example where the limit temperature is 280°C. When a resistance thermometer is used as a heater temperature sensor, for example, the low-temperature side dummy resistance 103 is set to 2013.14 (Ω) to correspond to the case where the measured temperature of the heater temperature sensor 14 is 270°C, which is the low-temperature side abnormal detection temperature. Similarly, the high-temperature side dummy resistance 104 is set to 2084.84 (Ω) to correspond to the case where the measured temperature of the heater temperature sensor 14 is 290°C, which is the high-temperature side abnormal detection temperature.

[0021] Returning to Figure 1, let's continue the explanation. The heater temperature sensor 14, the low-temperature dummy resistor 103, and the high-temperature dummy resistor 104 are switched ON / OFF by FET switches 221-223 via control signals from the control circuit 21, thereby switching between a connected state and a disconnected state. In addition, the presence or absence of heater current flowing to the heater 12 can be recognized by the firmware operating in the control circuit 21, as a signal is input to the control circuit 21 through the current detection circuit 24. The control circuit 21 is, for example, a CPU.

[0022] The control circuit 21 then performs abnormality detection of the heater temperature limit circuit 23 in the following manner. After power is turned on, the control circuit 21 first connects the high-temperature dummy resistor 104 and confirms that no heater current flows. Next, the control circuit 21 connects the low-temperature dummy resistor 103 and confirms that heater current flows. If both confirmations are successful, the control circuit 21 determines that the heater temperature limit circuit 23 is normal, connects the heater temperature sensor 14 to the circuit, and proceeds to the normal sequence. If heater current flows when the high-temperature dummy resistor 104 is connected, or if heater current does not flow when the low-temperature dummy resistor 103 is connected, the control circuit 21 issues an alarm via firmware.

[0023] In the event that the heater temperature limit circuit 23 malfunctions during operation, causing the heater 12 to remain constantly ON, if the control circuit 21 malfunctions in that state and the control signal remains constantly ON, overheating cannot be prevented. In this case, the pressure measuring device 10 according to this embodiment runs an abnormality detection sequence by the control circuit 21 to detect an abnormality in the heater temperature limit circuit 23. During the abnormality detection sequence, which is performed periodically during operation, when the high-temperature side dummy resistor 104 is switched on, heater current flows even though it should not, allowing the control circuit 21 to notify of the abnormality detection with an alarm.

[0024] In the pressure measuring device 10, the number of components increases due to the abnormality detection function, but the heater current can be shut off in the event of a single component failure. Figures 4A to 4D summarize the correspondence between faulty components and current shutoff methods when a thermistor is used. Similarly, Figures 5A to 5D summarize the correspondence between faulty components and current shutoff methods when a resistance thermometer is used. As shown in Figures 4A to 4D and 5A to 5D, the pressure measuring device 10 can detect any type of single component failure and shut off the heater current, regardless of whether a thermistor or resistance thermometer is used as the heater temperature sensor 14, thereby preventing accidents such as fires. In other words, the safety of the pressure measuring device 10 can be improved. In particular, the items circled in the column labeled "Features of the pressure measuring device 10" in Figures 4A to 4D and 5A to 5D are items newly realized by the pressure measuring device 10. In other words, the pressure measuring device 10 can be said to be safer than conventional technology.

[0025] [First Embodiment] [Example of a pressure measuring device's functional configuration] The following describes in more detail an example of an embodiment of the pressure measuring device 10 described above, referring back to Figure 1. The pressure measuring device 10 is a pressure detection device. As shown in Figure 1, the pressure measuring device 10 includes a pressure sensor 11, a heater 12, a heater power supply 13, a heater temperature sensor 14, a pressure receiving section temperature sensor 15, a first temperature sensor circuit power supply 16, and a second temperature sensor circuit power supply 17. The pressure measuring device 10 also includes a control circuit 21, an ADC (Analog to Digital Converter) 22, a heater temperature limit circuit 23, and a current detection circuit 24. Furthermore, the pressure measuring device 10 includes fixed resistors 101 and 102, low-temperature dummy resistors 103 and 104, and FET switches 211, 212, and 221-223.

[0026] The pressure sensor 11 is a diaphragm-type pressure sensor equipped with a vacuum chamber inside, which detects the pressure difference between the air pressure in the vacuum chamber and the air pressure in the room being measured by the displacement of the diaphragm. Examples of the air pressure to be measured include the air pressure inside the vacuum chamber of semiconductor manufacturing equipment.

[0027] The heater 12 is positioned to cover the outside of the pressure sensor 11. The heater 12 heats the pressure sensor 11 by generating heat. This heating maintains a high temperature around the diaphragm inside the pressure sensor 11, preventing contaminants contained in the gas introduced into the pressure sensor 11 from the room being measured, such as a vacuum chamber, from precipitation. The heater 12 is a band heater or the like, which includes a sheath heater or the like. The heater 12 generates heat and heats the pressure sensor 11 when a heater current supplied from the heater power supply 13 flows through it, i.e., when it is energized. The energization / de-energization of the heater current is controlled by a control circuit 21 such as a CPU.

[0028] However, if the heater 12's temperature exceeds a predetermined upper temperature threshold used to prevent an inappropriate temperature rise, the control circuit 21 cuts off the heater current and stops generating heat. Also, if the heater 12's temperature exceeds a predetermined limit temperature, which is a threshold used to prevent overheating of the heater 12, the heater temperature limit circuit 23 cuts off the heater current and stops generating heat. The limit temperature is a temperature that prevents accidents such as ignition, and is preferably determined from the configuration of the pressure sensor 11 and the heater 12. For example, the limit temperature can be set to 280°C.

[0029] The heater power supply 13 applies a voltage input from an external power supply (not shown) to the heater 12. As described later, when the control circuit 21 controls the flow of heater current to the heater 12, the heater power supply 13 supplies a heater current to the heater 12 corresponding to the applied voltage. As a result, the heater 12 generates heat, which heats the pressure sensor 11.

[0030] The first temperature sensor circuit power supply 16 receives current from an external power supply (not shown) and, depending on the on / off state of the FET switches 221 to 223, supplies it to either the heater temperature sensor 14, the low-temperature dummy resistor 103, or the high-temperature dummy resistor 104 via the fixed resistor 101. As a result, voltage values ​​corresponding to the fixed resistor 101 and the heater temperature sensor 14, the low-temperature dummy resistor 103, or the high-temperature dummy resistor 104 are input to the heater temperature limit circuit 23 and the ADC 22.

[0031] The second temperature sensor circuit power supply 17 receives current from an external power supply (not shown) and supplies it to the pressure-receiving temperature sensor 15 via a fixed resistor 102. As a result, a voltage value corresponding to the fixed resistor 102 and the pressure-receiving temperature sensor 15 is input to the ADC 22.

[0032] The heater temperature sensor 14 is installed at a predetermined location on the heater 12, detects the temperature of the heater 12, and outputs the detected temperature to the control circuit 21. The pressure sensor temperature sensor 15 is installed inside or on the outer surface of the pressure sensor 11, detects the temperature of the pressure sensor 11, and outputs the detected temperature to the control circuit 21. Each of the heater temperature sensor 14 and the pressure sensor temperature sensor 15 is configured to include elements such as thermocouples and thermistors that convert temperature into voltage values, and here they output a voltage value indicating temperature to perform temperature detection and output information on the detected temperature.

[0033] The control circuit 21, ADC 22, heater temperature limit circuit 23, and FET switches 211 and 212 control the heater current flowing through the heater 12, thereby controlling the heat generated by the heater 12 and controlling the temperature of the heater 12. The control circuit 21, low-temperature dummy resistors 103 and 104, and FET switches 222 and 223 constitute the abnormality detection unit 20. The abnormality detection unit 20 causes the heater temperature limit circuit 23 to perform an operation that would occur if the heater 12 temperature were at a predetermined temperature, detects an abnormality in the heater temperature limit circuit 23, and issues an alarm when an abnormality is detected. For example, when the pressure measuring device 10 is powered on, the abnormality detection unit 20 detects an abnormality in the heater temperature limit circuit 23 by sending predetermined voltage values ​​indicating high temperature and voltage values ​​indicating low temperature to the heater temperature limit circuit 23. Details of each part are described below.

[0034] FET switches 211 and 212 are switching elements that switch whether or not heater current from the heater power supply 13 flows to the heater 12. The drain terminal of FET switch 211 is connected to the other end of the heater 12, which is connected to the heater power supply 13 at one end. The source terminal of FET switch 211 is connected to the drain terminal of FET switch 212. A heater temperature limit circuit 23 is connected to the gate terminal of FET switch 211. The source terminal of FET switch 212 is connected to ground. A control circuit 21 that controls the current flowing to the heater 12 is connected to the gate terminal of FET switch 212.

[0035] With the connections described above, the FET switches 211 and 212 are placed on the current path of the heater current that flows from the heater power supply 13 through the heater 12 to ground. When both FET switches 211 and 212 are in the ON state, heater current flows to the heater 12, causing the heater 12 to generate heat.

[0036] The low-temperature dummy resistor 103 is a resistor that supplies a predetermined voltage corresponding to a predetermined temperature for detecting an abnormality in the heater temperature limit circuit 23 to the heater temperature limit circuit 23. The voltage applied to the heater temperature limit circuit 23 is determined by the voltage division between the low-temperature dummy resistor 103 and the fixed resistor 101. For example, the low-temperature dummy resistor 103 is used to apply a voltage to the heater temperature limit circuit 23 that indicates the low-temperature abnormality detection temperature. Here, the low-temperature abnormality detection temperature is a temperature lower than the limit temperature, and it is a temperature at which it is possible to determine that there is an abnormality if heater current does not flow through the heater temperature limit circuit 23. Preferably, the low-temperature abnormality detection temperature is determined by the capacity of the heater temperature limit circuit 23, etc. The low-temperature dummy resistor 103 is connected to or disconnected from the circuit by turning the FET switch 222 on or off. This low-temperature dummy resistor 103 is an example of a "second dummy resistor".

[0037] The high-temperature dummy resistor 104 is also a resistor that supplies a predetermined voltage corresponding to a predetermined temperature for detecting an abnormality in the heater temperature limit circuit 23 to the heater temperature limit circuit 23. The voltage applied to the heater temperature limit circuit 23 is determined by the voltage division between the high-temperature dummy resistor 104 and the fixed resistor 101. For example, the high-temperature dummy resistor 104 is used to supply a voltage indicating the high-temperature abnormality detection temperature to the heater temperature limit circuit 23. Here, the high-temperature abnormality detection temperature is a temperature higher than the limit temperature, and it is a temperature at which it is possible to determine that there is an abnormality if heater current is flowing through the heater temperature limit circuit 23 at this temperature. It is preferable that the high-temperature abnormality detection temperature is determined by the capabilities of the heater temperature limit circuit 23, etc. The high-temperature dummy resistor 104 is connected to or disconnected from the circuit by turning the FET switch 223 on or off. This high-temperature dummy resistor 104 is an example of a "first dummy resistor".

[0038] The resistance values ​​of the low-temperature dummy resistors 103 and 104 can be determined, for example, by using the relationship between the thermistor characteristics and the dummy resistance values ​​shown in Figure 2A, when a thermistor is used as the heater temperature sensor 14. Specifically, the resistance values ​​of the low-temperature dummy resistors 103 and 104 are determined by the following procedure. First, the limit temperature that prevents overheating of the heater temperature limit circuit 23 is determined. Next, the low-temperature abnormal detection temperature, which is lower than the limit temperature, and the high-temperature abnormal detection temperature, which is higher than the limit temperature, are determined. Then, the resistance value corresponding to the low-temperature abnormal detection temperature in the graph of Figure 2A is determined as the resistance value of the low-temperature dummy resistor 103. Also, the resistance value corresponding to the high-temperature abnormal detection temperature in the graph of Figure 2A is determined as the resistance value of the high-temperature dummy resistor 104.

[0039] Furthermore, the resistance values ​​of the low-temperature dummy resistors 103 and 104 can be determined, for example, when a resistance thermometer is used as the heater temperature sensor 14, using the relationship between the thermistor characteristics and the dummy resistance values ​​shown in Figure 2B. Specifically, the resistance values ​​of the low-temperature dummy resistors 103 and 104 are determined by the following procedure. First, the limit temperature that prevents overheating of the heater temperature limit circuit 23 is determined. Next, the low-temperature abnormal detection temperature, which is lower than the limit temperature, and the high-temperature abnormal detection temperature, which is higher than the limit temperature, are determined. Then, the resistance value corresponding to the low-temperature abnormal detection temperature in the graph of Figure 2B is determined as the resistance value of the low-temperature dummy resistor 103. Also, the resistance value corresponding to the high-temperature abnormal detection temperature in the graph of Figure 2B is determined as the resistance value of the high-temperature dummy resistor 104.

[0040] If a thermistor is used as the heater temperature sensor 14, for example, based on the measurement results when the limit temperature shown in Figure 3A is 280°C, the high-temperature abnormality detection temperature can be set to 290°C by using a high-temperature side dummy resistor 104 that results in a measured temperature of 290°C. Also, based on the measurement results when the limit temperature shown in Figure 3A is 280°C, the low-temperature side abnormality detection temperature can be set to 270°C by using a low-temperature side dummy resistor 103 that results in a measured temperature of 270°C.

[0041] Similarly, when a resistance thermometer is used as the heater temperature sensor 14, for example, based on the measurement results when the limit temperature shown in Figure 3B is 280°C, the high-temperature abnormal detection temperature can be set to 290°C by using a high-temperature side dummy resistor 104 that has a measured temperature of 290°C. Also, based on the measurement results when the limit temperature shown in Figure 3B is 280°C, the low-temperature side abnormal detection temperature can be set to 270°C by using a low-temperature side dummy resistor 103 that has a measured temperature of 270°C.

[0042] Furthermore, in this embodiment, the resistance values ​​of the low-temperature dummy resistor 103 and the high-temperature dummy resistor 104 were determined using measurement results. However, the method is not limited to this; the values ​​can also be determined by theoretical calculations based on thermistor characteristics, resistance thermometer characteristics, etc.

[0043] The control circuit 21 is a processor such as a CPU. The control circuit 21 executes a program recorded in a memory device (not shown) and operates based on the data stored in the memory device. The processor may be a microcomputer including a memory device. The control circuit 21 may also be various logic circuits. The gate terminal of the FET switch 212 is connected to the control circuit 21. The ADC 22 is also connected to the control circuit 21.

[0044] The control circuit 21 receives temperature information from the pressure sensor 11 via the ADC 22. The control circuit 21 then outputs an ON signal (e.g., a High signal) or OFF signal (e.g., a Low signal) to the FET switch 212 to control the on / off state of the FET switch 212, so that the temperature of the pressure sensor 11 input from the ADC 22 reaches a preset target temperature. The control circuit 21 switches the FET switch 212 on or off using feedback control, such as PID (Proportional Integral Differential) control.

[0045] Furthermore, the control circuit 21 has an upper temperature threshold used to prevent an inappropriate temperature rise of the heater 12. The control circuit 21 receives temperature information of the heater 12 from the ADC 22. It then determines whether the temperature of the heater 12 input from the ADC 22 exceeds the upper temperature threshold. If the temperature of the heater 12 exceeds the upper temperature threshold, the control circuit 21 determines that the temperature of the heater 12 is higher than necessary, and, prioritizing feedback control to the FET switch 212, supplies an off signal (for example, a low signal) to the FET switch 212, thereby turning off the FET switch 212. This cuts off the power supply to the heater 12, and the heating of the heater 12 stops.

[0046] Furthermore, the control circuit 21 performs abnormality detection of the heater temperature limit circuit 23 when power is turned on to the pressure measuring device 10 and operation begins. Specifically, the control circuit 21 turns on the FET switch 212 and then performs abnormality detection by high-temperature abnormality detection processing and low-temperature abnormality detection processing as described below.

[0047] In the high-temperature abnormality detection process, the control circuit 21 inputs an off signal (e.g., a low signal) to the gates of FET switches 221 and 222 to turn off FET switches 221 and 222, disconnecting the heater temperature sensor 14 and the low-temperature dummy resistor 103 from the circuit. Next, the control circuit 21 inputs an on signal (e.g., a high signal) to the gate of FET switch 223 to turn on FET switch 223, connecting the high-temperature dummy resistor 104 to the circuit. As a result, a voltage value indicating the high-temperature abnormality detection temperature, defined by the resistance value of the high-temperature dummy resistor 104, is input to the heater temperature limit circuit 23.

[0048] Subsequently, the control circuit 21 receives notification from the current detection circuit 24 regarding the presence or absence of heater current flowing to the heater 12. If no heater current is flowing, the control circuit 21 determines that the heater temperature limit circuit 23 is operating normally. In that case, the control circuit 21 proceeds to the next low-temperature abnormality detection process.

[0049] In contrast, if heater current is flowing, the control circuit 21 determines that the heater temperature limit circuit 23 is malfunctioning because, although the heater current should be cut off by the heater temperature limit circuit 23, it is still flowing. In this case, the control circuit 21 signals an alarm, for example, by illuminating a warning light. The user can confirm the malfunction of the heater temperature limit circuit 23 by checking the alarm.

[0050] In the low-temperature anomaly detection process, the control circuit 21 inputs an off signal (e.g., a low signal) to the gates of FET switches 221 and 223 to turn off FET switches 221 and 223, disconnecting the heater temperature sensor 14 and the high-temperature dummy resistor 104 from the circuit. Next, the control circuit 21 inputs an on signal (e.g., a high signal) to the gate of FET switch 222 to turn on FET switch 222, connecting the low-temperature dummy resistor 103 to the circuit. As a result, a voltage value indicating the low-temperature anomaly detection temperature, defined by the resistance value of the low-temperature dummy resistor 103, is input to the heater temperature limit circuit 23.

[0051] Subsequently, the control circuit 21 receives notification from the current detection circuit 24 regarding the presence or absence of heater current, which is the current flowing to the heater 12. If heater current is flowing, the control circuit 21 determines that the heater temperature limit circuit 23 is operating normally. The control circuit 21 then inputs an off signal (e.g., a low signal) to the gates of FET switches 222 and 223 to turn off FET switches 222 and 223, and disconnects the low-temperature dummy resistors 103 and 104 from the circuit. Next, the control circuit 21 inputs an on signal (e.g., a high signal) to the gate of FET switch 221 to turn on FET switch 221, and connects the heater temperature sensor 14 to the circuit. After that, the control circuit 21 proceeds to the normal sequence, such as measuring the temperature of the pressure sensor 11 and the heater 12.

[0052] In contrast, if no heater current is flowing, the control circuit 21 determines that the heater temperature limit circuit 23 is malfunctioning because, although the FET switch 211 should not be turned off and heater current should be flowing since the limit temperature has not been reached, the heater current is being cut off by the heater temperature limit circuit 23. In this case, the control circuit 21 signals an alarm, for example, by illuminating a warning light. The user can confirm the malfunction of the heater temperature limit circuit 23 by checking the alarm.

[0053] In this way, the abnormality detection unit 20 connects the high-temperature side dummy resistor 104 to the heater temperature limit circuit 23 and detects abnormal operation of the heater temperature limit circuit 23 when the temperature is higher than the limit temperature. Next, the abnormality detection unit 20 connects the low-temperature side dummy resistor 103 to the heater temperature limit circuit 23 and detects abnormal operation of the heater temperature limit circuit 23 when the temperature is lower than the limit temperature.

[0054] The ADC22 is connected to the control circuit 21. The ADC22 converts the temperature of the pressure sensor 11, which is represented by the voltage value detected and output by the pressure sensor temperature sensor 15, into digital data and supplies it to the control circuit 21. The ADC22 also converts the voltage value representing the temperature of the heater 12, which is indicated by the voltage value detected and output by the heater temperature sensor 14, into digital data and supplies it to the control circuit 21.

[0055] The heater temperature limit circuit 23 has a limit temperature, which is a temperature threshold for determining if the heater 12 has overheated. The heater temperature limit circuit 23 receives the temperature of the heater 12 detected by the heater temperature sensor 14 as input. The heater temperature limit circuit 23 compares the input temperature with the limit temperature. The limit temperature may be the same as the upper threshold of the control circuit 21, or it may be a different value (in particular, a value higher than the upper threshold).

[0056] The heater temperature limit circuit 23 supplies an ON signal to the gate of the FET switch 211, turning on the FET switch 211 when the input temperature of the heater 12 is below the limit temperature, that is, when the temperature of the heater 12 is within the normal range. Conversely, the heater temperature limit circuit 23 supplies an OFF signal to the gate of the FET switch 211, turning off the FET switch 211 when the input temperature of the heater 12 exceeds the limit temperature, that is, when the temperature of the heater 12 is overheated. By turning off the FET switch 211, the heater temperature limit circuit 23 cuts off the power supply to the heater 12 and stops the heater 12 from generating heat.

[0057] The current detection circuit 24 detects whether or not heater current is flowing from the heater power supply 13 through the heater 12. If both FET switches 211 or 212 are on, the current detection circuit 24 detects that heater current is flowing. Conversely, if at least one of the FET switches 211 or 212 is off, the current detection circuit 24 detects that heater current is not flowing. The current detection circuit 24 then notifies the control circuit 21 of the heater current detection result.

[0058] [An example of fault diagnosis processing in the first embodiment] Figure 6 is a flowchart of the fault diagnosis process for the heater temperature limit circuit using the pressure measuring device according to the first embodiment. Next, referring to Figure 6, the flow of the fault diagnosis process for the heater temperature limit circuit 23 using the pressure measuring device 10 according to this embodiment will be described.

[0059] Power is turned on to the pressure measuring device 10 (step S101).

[0060] The control circuit 21 turns on FET switches 212 and 223 and turns off FET switches 221 and 222. As a result, the control circuit 21 connects the high-temperature dummy resistor 104 to the circuit (step S102).

[0061] Then, the control circuit 21 determines whether the heater current is 0(A) or not based on the heater current detection result input from the current detection circuit 24 (step S103).

[0062] If the heater current is not 0 (A) (step S103: negative), the control circuit 21 detects an abnormality in the heater temperature limit circuit 23 and sounds an alarm (step S108).

[0063] In contrast, if the heater current is 0 (A) (step S103: affirmative), the control circuit 21 then turns on FET switches 212 and 222 and turns off FET switches 221 and 223. This causes the control circuit 21 to connect the low-temperature dummy resistor 103 to the circuit (step S104).

[0064] Then, the control circuit 21 determines whether the heater current is 0(A) or not based on the heater current detection result input from the current detection circuit 24 (step S105).

[0065] If the heater current is 0 (A) (step S105: affirmative), the control circuit 21 detects an abnormality in the heater temperature limit circuit 23 and sounds an alarm (step S108).

[0066] In contrast, if the heater current is not 0 (A) (step S105: negative), the control circuit 21 determines that the heater temperature limit circuit 23 is functioning correctly. The control circuit 21 then turns on the FET switch 221 and turns off the FET switches 222 and 223. As a result, the control circuit 21 connects the heater temperature sensor 14 to the circuit (step S106).

[0067] Subsequently, the control circuit 21 performs a normal sequence of operations, such as controlling the heater 12 and measuring the pressure sensor 11 and the heater 12, as well as measuring the temperature (step S107).

[0068] [Effects of the First Embodiment and its Modified Forms] As described above, the pressure measuring device 10 according to this embodiment applies a high-temperature abnormal detection temperature to the heater temperature limit circuit 23 using a high-temperature dummy resistor 104, and detects an abnormality in the heater temperature limit circuit 23 based on the presence or absence of heater current flowing at that time, thereby sounding an alarm. Furthermore, the pressure measuring device 10 according to this embodiment applies a low-temperature abnormal detection temperature to the heater temperature limit circuit 23 using a low-temperature dummy resistor 103, and detects an abnormality in the heater temperature limit circuit 23 based on the presence or absence of heater current flowing at that time, thereby sounding an alarm. This makes it possible to make the user aware of a malfunction in the heater temperature limit circuit 23. In other words, it is possible to avoid accidents such as fires that would occur if the control circuit 21 malfunctioned while the pressure measuring device 10 was still in use with a faulty heater temperature limit circuit 23. Thus, it is possible to improve the safety of the pressure measuring device 10.

[0069] In the above explanation, the heater temperature limit circuit 23 abnormality was detected by continuously interrupting the heater current using the low-temperature dummy resistor 103. However, there is no risk of fire or other dangers when the heater current is continuously interrupted. Therefore, the control circuit 21 may perform high-temperature abnormality detection processing using the high-temperature dummy resistor 104, which poses a fire risk, and may not perform low-temperature abnormality detection processing using the low-temperature dummy resistor 103. Also, in this embodiment, the control circuit 21 performs low-temperature abnormality detection processing after high-temperature abnormality detection processing, but this order may be reversed.

[0070] Furthermore, in this embodiment, the control circuit 21 detected an abnormality in the heater temperature limit circuit 23 when the power was turned on, but the control circuit 21 may repeatedly detect an abnormality in the heater temperature limit circuit 23 at predetermined timings, such as when the pressure sensor 11 is not measuring pressure. For example, this may be done after power is turned on to the pressure measuring device 10 but before current is started to flow to the heater 12. In addition, the detection of an abnormality in the heater temperature limit circuit 23 may be performed during maintenance, etc.

[0071] [Second Embodiment] Figure 7 is a block diagram of a pressure measuring device according to the second embodiment. In this embodiment, the pressure measuring device 10 applies a predetermined voltage to the heater temperature limit circuit 23 based on a signal from the control circuit 21, and performs an operational test of the heater temperature limit circuit 23. In the following description, the operation of each part, which is the same as in the first embodiment, will be omitted.

[0072] In this embodiment, the control circuit 21 and the FET switch 224 constitute the abnormality detection unit 20. The abnormality detection unit 20 causes the heater temperature limit circuit 23 to perform an operation when the heater 12 temperature reaches a predetermined temperature, detects an abnormality in the heater temperature limit circuit 23, and issues an alarm when an abnormality is detected. The details of the abnormality detection unit 20 will be described below.

[0073] The control circuit 21 incorporates a DA (Digital to Analog) converter. Hereinafter, the DA converter incorporated in the control circuit 21 will be referred to as the built-in DA converter. The control circuit 21 also pre-stores predetermined voltages corresponding to predetermined temperatures used for detecting abnormalities in the heater temperature limit circuit 23. For example, the control circuit 21 stores information on voltage values ​​corresponding to high-temperature abnormality detection temperatures and information on voltage values ​​corresponding to low-temperature abnormality detection temperatures.

[0074] Figure 8A shows the relationship between measured temperature and corresponding voltage when an NTC thermistor is used as a heater temperature sensor. For example, the case where the limit temperature is 280°C, the high-temperature abnormal detection temperature is 290°C, and the low-temperature abnormal detection temperature is 270°C is explained. In this case, the fixed resistor 101 is 2700 (Ω). An NTC thermistor is used as the heater temperature sensor 14, and the resistance value of the heater temperature sensor 14 is 29 (Ω) at 270°C and 22 (Ω) at 290°C. Furthermore, both the first temperature sensor circuit power supply 16 and the second temperature sensor circuit power supply 17 are 2.5 (V). In this case, for example, the control circuit 21 holds a voltage value of 0.0266 (V) equivalent to the low-temperature abnormal detection temperature of 270°C. Also, for example, the control circuit 21 holds a voltage value of 0.0202 (V) equivalent to the high-temperature abnormal detection temperature of 290°C.

[0075] Figure 8B shows the relationship between the measured temperature and the corresponding dummy resistance value when a resistance thermometer is used as a heater temperature sensor. Next, we will explain the case where a resistance thermometer is used as the heater temperature sensor 14. Here again, we will explain the case where the limit temperature is 280°C, the high-temperature abnormal detection temperature is 290°C, and the low-temperature abnormal detection temperature is 270°C. Here again, the fixed resistor 101 is 2700 (Ω). The resistance value of the heater temperature sensor 14 is 2013.14 (Ω) at 270°C and 2084.84 (Ω) at 290°C. Furthermore, both the first temperature sensor circuit power supply 16 and the second temperature sensor circuit power supply 17 are 2.5 (V). In this case, for example, the control circuit 21 holds a voltage value of 1.07 (V) equivalent to the low-temperature abnormal detection temperature of 270°C. Also, for example, the control circuit 21 holds a voltage value of 1.09 (V) equivalent to the high-temperature abnormal detection temperature of 290°C.

[0076] The control circuit 21 turns on the FET switch 212. Next, the control circuit 21 turns off the FET switch 221, disconnecting the heater temperature sensor 14 from the circuit. Next, the control circuit 21 turns on the FET switch 224. Then, the control circuit 21 performs abnormality detection by high-temperature abnormality detection processing and low-temperature abnormality detection processing as described below.

[0077] In the high-temperature anomaly detection process, the control circuit 21 outputs a voltage equivalent to the high-temperature anomaly detection temperature from the built-in DA converter. Based on this, the control circuit 21 applies a voltage equivalent to the high-temperature anomaly detection temperature to the heater temperature limit circuit 23. For example, if an NTC thermistor is used as the heater temperature sensor 14, the control circuit 21 applies 0.0202(V) to the heater temperature limit circuit 23 based on the voltage value equivalent to 290°C, the high-temperature anomaly detection temperature shown in Figure 8A. Alternatively, if a resistance thermometer is used as the heater temperature sensor 14, the control circuit 21 applies 1.09(V) to the heater temperature limit circuit 23 based on the voltage value equivalent to 290°C, the high-temperature anomaly detection temperature shown in Figure 8B.

[0078] Subsequently, the control circuit 21 receives notification from the current detection circuit 24 regarding the presence or absence of heater current flowing to the heater 12. If no heater current is flowing, the control circuit 21 determines that the heater temperature limit circuit 23 is operating normally. In that case, the control circuit 21 proceeds to the next low-temperature abnormality detection process.

[0079] In contrast, if heater current is flowing, the control circuit 21 determines that the heater temperature limit circuit 23 is malfunctioning because, although the heater current should be cut off by the heater temperature limit circuit 23, it is still flowing. In this case, the control circuit 21 signals an alarm, for example, by illuminating a warning light. The user can confirm the malfunction of the heater temperature limit circuit 23 by checking the alarm.

[0080] In the low-temperature anomaly detection process, the control circuit 21 outputs a voltage equivalent to the low-temperature anomaly detection temperature from the built-in DA converter. Based on this, the control circuit 21 applies a voltage equivalent to the low-temperature anomaly detection temperature to the heater temperature limit circuit 23. For example, if an NTC thermistor is used as the heater temperature sensor 14, the control circuit 21 applies 0.0266(V) to the heater temperature limit circuit 23 based on the voltage value equivalent to 270°C, which is the low-temperature anomaly detection temperature shown in Figure 8A. If a resistance thermometer is used as the heater temperature sensor 14, the control circuit 21 applies 1.07(V) to the heater temperature limit circuit 23 based on the voltage value equivalent to 270°C, which is the low-temperature anomaly detection temperature shown in Figure 8B.

[0081] Subsequently, the control circuit 21 receives notification from the current detection circuit 24 regarding the presence or absence of heater current, which is the current flowing to the heater 12. If heater current is flowing, the control circuit 21 determines that the heater temperature limit circuit 23 is operating normally. Then, the control circuit 21 turns off the FET switch 224. Next, the control circuit 21 turns on the FET switch 221 and connects the heater temperature sensor 14 to the circuit. After that, the control circuit 21 proceeds to the normal sequence, such as monitoring the temperature of the pressure sensor 11 and the heater 12.

[0082] In contrast, if no heater current is flowing, the control circuit 21 determines that the heater temperature limit circuit 23 is malfunctioning because, although heater current should be flowing, it is being interrupted by the heater temperature limit circuit 23. In this case, the control circuit 21 signals an alarm, for example, by illuminating a warning light. The user can confirm the malfunction of the heater temperature limit circuit 23 by checking the alarm.

[0083] [An example of fault diagnosis processing in the second embodiment] Figure 9 is a flowchart of the fault diagnosis process for the heater temperature limit circuit using the pressure measuring device according to the second embodiment. Next, referring to Figure 9, the flow of the fault diagnosis process for the heater temperature limit circuit 23 using the pressure measuring device 10 according to this embodiment will be explained.

[0084] Power is turned on to the pressure measuring device 10 (step S201).

[0085] The control circuit 21 turns on the FET switch 224 and turns off the FET switch 221. Then, the control circuit 21 outputs a voltage from the built-in DA converter equivalent to the high-temperature abnormality detection temperature and applies it to the heater temperature limit circuit 23 (step S202).

[0086] Then, the control circuit 21 determines whether the heater current is 0(A) or not based on the heater current detection result input from the current detection circuit 24 (step S203).

[0087] If the heater current is not 0 (A) (step S203: negative), the control circuit 21 detects an abnormality in the heater temperature limit circuit 23 and sounds an alarm (step S208).

[0088] In contrast, if the heater current is 0 (A) (step S203: affirmative), the control circuit 21 then outputs a voltage equivalent to the low-temperature abnormality detection temperature from the built-in DA converter and applies it to the heater temperature limit circuit 23 (step S204).

[0089] Then, the control circuit 21 determines whether the heater current is 0(A) or not based on the heater current detection result input from the current detection circuit 24 (step S205).

[0090] If the heater current is 0 (A) (step S205: affirmative), the control circuit 21 detects an abnormality in the heater temperature limit circuit 23 and sounds an alarm (step S208).

[0091] In contrast, if the heater current is not 0 (A) (step S205: negative), the control circuit 21 determines that the heater temperature limit circuit 23 is functioning correctly. The control circuit 21 then turns on the FET switch 221 and turns off the FET switch 224. As a result, the control circuit 21 connects the heater temperature sensor 14 to the circuit (step S206).

[0092] Subsequently, the control circuit 21 executes a normal sequence of operations, such as controlling the heater 12 and measuring the pressure sensor 11 and the heater 12, as well as measuring the temperature (step S207).

[0093] [Effects of the second embodiment and its modified form] As described above, in this embodiment, the pressure measuring device 10 performs abnormality detection by having the control circuit 21 output a voltage equivalent to a predetermined high-temperature abnormality detection temperature and a voltage equivalent to a predetermined low-temperature abnormality detection temperature from the built-in DA converter and applying them to the heater temperature limit circuit 23. In this way, even by applying a predetermined voltage to the heater temperature limit circuit 23 in response to a signal from the control circuit 21 to test the operation of the heater temperature limit circuit 23, it is possible to make the user aware of a malfunction in the heater temperature limit circuit 23. In other words, it is possible to avoid accidents such as fires that would occur if the pressure measuring device 10 were to continue to be used while the heater temperature limit circuit 23 is malfunctioning and the control circuit 21 malfunctions in that state. Therefore, it is possible to improve the safety of the pressure measuring device 10.

[0094] The above describes an example of an embodiment, but these are illustrative examples, and this embodiment is not limited to the above description. The configuration and details of the embodiments, including the aspects described in the disclosure section of the invention, can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. Furthermore, each embodiment can be combined in any way that does not contradict each other. [Explanation of Symbols]

[0095] 10. Pressure measuring device 11. Pressure sensor 12 Heaters 13 Heater power supply 14. Heater temperature sensor 15 Pressure-receiving temperature sensor 16. Power supply for the first temperature sensor circuit 17. Power supply for the second temperature sensor circuit 20 Anomaly detection unit 21 Control circuits 22 ADC 23. Heater temperature limit circuit 24 Current sensing circuit 101,102 Fixed resistance 103 Low-temperature dummy resistor 104 High-temperature side dummy resistor 211, 212, 221~224 FET switches

Claims

1. Pressure sensor and A heater for heating the pressure sensor, A heater temperature sensor for measuring the temperature of the heater, A pressure-receiving temperature sensor for measuring the temperature of the pressure sensor, A control circuit controls heating by the heater based on the temperature of the pressure sensor measured by the pressure-receiving temperature sensor, A heater temperature limit circuit is provided that, when a voltage corresponding to the heater temperature is applied, cuts off the heater drive current based on the heater temperature measured by the heater temperature sensor, The system includes a dummy resistor that applies a predetermined voltage to the heater temperature limit circuit when the heater temperature reaches a predetermined temperature, and by connecting the dummy resistor to the heater temperature limit circuit, the system causes the heater temperature limit circuit to perform the operation required when the heater temperature reaches the predetermined temperature, thereby detecting an abnormality in the heater temperature limit circuit and sounding an alarm when such an abnormality is detected. A pressure measuring device characterized by being equipped with the following features.

2. The pressure measuring device according to claim 1, characterized in that the abnormality detection unit has a first dummy resistor and a second dummy resistor with different resistance values ​​as the dummy resistors, and by switching between the first dummy resistor and the second dummy resistor and connecting them to the heater temperature limit circuit, it detects an abnormality in the heater temperature limit circuit based on the operation of the heater temperature limit circuit when different voltages are applied to the heater temperature limit circuit.

3. The heater temperature limit circuit cuts off the heater drive current when the heater temperature reaches a predetermined limit temperature. The abnormality detection unit connects the first dummy resistor to the heater temperature limit circuit to detect an abnormality in the operation of the heater temperature limit circuit when the predetermined temperature is higher than the limit temperature, and connects the second dummy resistor to the heater temperature limit circuit to detect an abnormality in the operation of the heater temperature limit circuit when the predetermined temperature is lower than the limit temperature. The pressure measuring device according to feature 2.

4. The heater temperature limit circuit cuts off the heater drive current based on the heater temperature when a voltage corresponding to the heater temperature is applied. The abnormality detection unit detects an abnormality in the heater temperature limit circuit when the temperature is predetermined by applying a predetermined voltage corresponding to the predetermined temperature to the heater temperature limit circuit. The pressure measuring device according to feature 1.

5. Pressure sensor and A heater for heating the pressure sensor, A heater temperature sensor for measuring the temperature of the heater, A pressure-receiving temperature sensor for measuring the temperature of the pressure sensor, A control circuit controls heating by the heater based on the temperature of the pressure sensor measured by the pressure-receiving temperature sensor, A control method for a pressure measuring device comprising a heater temperature limit circuit that cuts off the drive current of the heater based on the heater temperature measured by the heater temperature sensor by applying a voltage corresponding to the heater temperature of the heater, The aforementioned pressure measuring device The device has a dummy resistor that applies a predetermined voltage to the heater temperature limit circuit when the heater temperature reaches a predetermined temperature, and by connecting the dummy resistor to the heater temperature limit circuit, the heater temperature limit circuit is made to perform the operation required when the heater temperature reaches the predetermined temperature, thereby detecting an abnormality in the heater temperature limit circuit. An alarm will be sounded if the aforementioned abnormality is detected. A control method for a pressure measuring device, characterized by the following features.

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