Heater control device and vacuum gauge

Abstract

To suppress increase of heater temperature to be unnecessarily high, with high accuracy.SOLUTION: A vacuum gauge 10 comprises a control circuit 22 performing feedback control on the temperature of a heater 12 based on the temperature of a pressure sensor 11. The control circuit 22 turns off a transistor 21C, and forcibly cuts off the electric conduction of the heater 12 when the temperature of the heater 12 detected by a first temperature sensor 14 becomes higher than a threshold value S1. Whereas, redundant first and second limit circuits 25 and 26 of the vacuum gauge 10 also monitor the temperature of the heater 12 detected by the first temperature sensor 14 individually, and turn off a transistor 21A or 21B when the temperature of the heater 12 detected by the first temperature sensor 14 becomes higher than a threshold value S2. Thereby, the electric conduction of the heater 12 is forcibly cut off.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a heater control device and a vacuum gauge. [Background technology]

[0002] A vacuum gauge having a pressure sensor may have a heater surrounding the outer circumferential surface of the pressure sensor, as disclosed in Patent Document 1. This heater is controlled by a heater control unit provided in the vacuum gauge, and heats the inside of the pressure sensor (self-heating), thereby keeping the temperature around the diaphragm in the pressure sensor at a high temperature at which contaminants will not precipitate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-7906 A Summary of the Invention [Problem to be solved by the invention]

[0004] The heater control unit controls the heat generated by the heater, but if the heater control unit goes out of control and is unable to control the heat generated by the heater, the heater temperature may become higher than necessary. Therefore, it is conceivable to provide a limit circuit in the vacuum gauge that controls the heater so that it does not generate any more heat by preventing current from flowing through the heater when it detects that the heater temperature is higher than a predetermined temperature. However, if the vacuum gauge is used in a state where a malfunction occurs in the limit circuit without noticing this, the limit circuit may not operate when the heater control unit goes out of control, and the heater may become higher than necessary. This is also true for heaters in general.

[0005] An object of the present invention is to prevent the heater from becoming overly hot with high certainty. [Means for solving the problem]

[0006] In order to solve the above problems, a heater control device according to a first aspect of the present invention includes a control circuit configured to control a temperature of a heater by controlling a current flowing through the heater, a first limit circuit that operates to prevent the current from flowing to the heater when the temperature of the heater detected by a first temperature sensor exceeds a first threshold, and a second limit circuit, which is a redundant version of the first limit circuit and operates to prevent the current from flowing to the heater when the temperature detected by the first temperature sensor exceeds the first threshold.

[0007] The control circuit may perform control not to supply current to the heater when the temperature detected by the first temperature sensor exceeds a second threshold value.

[0008] The heater control device may further include a first switching element provided on a current path of the current and switched to an off state where the current does not flow based on a signal output by the first limit circuit, a second switching element provided on the current path and switched to an off state where the current does not flow based on a signal output by the second limit circuit, and a third switching element provided on the current path and switched to an off state where the current does not flow based on a signal output by the control circuit.

[0009] The heater control device may further include a fourth switching element arranged on the current path and switched to an off state in which no current flows through the current path based on an off signal from the first limit circuit, and a fifth switching element arranged on the current path and switched to an off state in which no current flows through the current path when at least one of the signal from the control circuit and the signal from the second limit circuit is an off signal.

[0010] The heater control device may further include a logic gate element that outputs an off signal when at least one of the signal from the control circuit and the signal from the second limit circuit is an off signal, and the fifth switching element may be switched to the off state when the off signal is input from the logic gate element.

[0011] In order to solve the above-mentioned problems, a vacuum gauge according to a second aspect of the present invention comprises the above-mentioned heater control device, the heater, and a diaphragm-type pressure sensor heated by the heater, and the control circuit controls the heat generation of the heater so that the temperature of the pressure sensor becomes a predetermined temperature. Effect of the Invention

[0012] According to the present invention, it is possible to highly reliably prevent the heater from reaching an unnecessarily high temperature. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram showing the configuration of a vacuum gauge according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram showing the configuration of a vacuum gauge according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] (First embodiment) A vacuum gauge 10 according to a first embodiment of the present invention will now be described with reference to the drawings. The vacuum gauge 10 is formed as a diaphragm vacuum gauge.

[0015] The vacuum gauge 10 includes a pressure sensor 11, a heater 12, a heater power supply circuit 13, a second temperature sensor 15, a first temperature sensor 14, and a heater control device 20.

[0016] The pressure sensor 11 is a diaphragm-type pressure sensor that has a vacuum chamber inside and detects the pressure difference between the air pressure in the vacuum chamber and the air pressure in the room to be measured by the displacement of a diaphragm. The air pressure to be measured may be, for example, the air pressure in a vacuum chamber of a semiconductor manufacturing device.

[0017] The heater 12 generates heat to heat the pressure sensor 11. This heating keeps the temperature around the diaphragm in the pressure sensor high enough to prevent the deposition of contaminants contained in the gas introduced into the pressure sensor 11 from the room to be measured (such as a vacuum chamber). The heater 12 is, for example, a band heater including a sheath heater. The heater 12 generates heat when a heater current supplied from a heater power supply circuit 13 flows through it, that is, when it is energized, and heats the pressure sensor 11. The heater control device 20 controls whether the heater current is energized or not.

[0018] The heater power supply circuit 13 applies a voltage input from an external power supply (not shown) to the heater 12. As described below, when the heater control device 20 controls the flow of a heater current to the heater 12, the heater power supply circuit 13 passes a heater current corresponding to the applied voltage to the heater 12. This causes the heater 12 to generate heat, heating the pressure sensor 11.

[0019] The first temperature sensor 14 is provided at a predetermined position of the heater 12, detects the temperature of the heater 12, and outputs the detected temperature to the heater control device 20. The second temperature sensor 15 is provided inside or on the outer peripheral surface of the pressure sensor 11, detects the temperature of the pressure sensor 11, and outputs the detected temperature to the heater control device 20. Each of the first and second temperature sensors 14 and 15 is configured to include an element such as a thermocouple or a thermistor that converts temperature into a voltage value, and detects and outputs the temperature by outputting a voltage value indicative of the temperature.

[0020] The heater control device 20 controls the heater current flowing through the heater 12 to control the heat generated by the heater 12 and thereby control the temperature of the heater 12. The heater control device 20 has a circuit configuration including transistors 21A to 21C, a control circuit 22, ADCs (Analog to Digital Converters) 23 and 24, and first and second limit circuits 25 and .

[0021] The transistors 21A to 21C are switching elements that switch between flowing and not flowing a heater current from the heater power supply circuit 13 to the heater 12. Each of the transistors 21A to 21C is formed of a field effect transistor (FET).

[0022] The drain of transistor 21A is connected to one end of heater 12, the other end of which is connected to heater power supply circuit 13. The source of transistor 21A is connected to the drain of transistor 21B. The source of transistor 21B is connected to the drain of transistor 21C. The source of transistor 21C is connected to ground. With such connections, transistors 21A to 21C are provided on a current path R1 of a heater current flowing from heater power supply circuit 13 to the ground. Then, only when all of transistors 21A to 21C are in the on state can a heater current flow to heater 12, and heater 12 can generate heat.

[0023] A control circuit 22 that controls the current flowing through the heater 12 is connected to the gate of the transistor 21C. The control circuit 22 is composed of a processor such as a CPU (Central Processing Unit). The control circuit 22 operates by executing a program recorded in a storage unit (not shown) and based on data stored in the storage unit. The processor may be a microcomputer or the like that includes the storage unit. The control circuit 22 may be various types of logic circuits.

[0024] The ADC 23 is connected to the control circuit 22. The ADC 23 converts the temperature (voltage value) of the pressure sensor 11 detected and output by the second temperature sensor 15 into digital data and supplies it to the control circuit 22. The control circuit 22 outputs an on signal (e.g., a high signal) or an off signal (e.g., a low signal) to the transistor 21C to control the on / off of the transistor 21C so that the temperature from the ADC 23, i.e., the temperature of the pressure sensor 11, becomes a preset target temperature. The control circuit 22 turns the transistor 21C on / off by feedback control such as PID (Proportional-Integral-Differential) control.

[0025] The control circuit 22 is also connected to the ADC 24. The ADC 24 converts the temperature (voltage value) of the heater 12 detected and output by the first temperature sensor 14 into digital data and supplies it to the control circuit 22. The control circuit 22 determines whether the temperature from the ADC 24 exceeds a threshold value S1. If the temperature exceeds the threshold value S1, it means that the temperature of the heater 12 is higher than necessary, so that the control circuit 22 prioritizes the above feedback control and supplies an off signal (e.g., a Low signal) to the transistor 21C to turn off the transistor 21C. This cuts off the power supply to the heater 12, and the heater 12 stops generating heat.

[0026] A first limit circuit 25 is connected to the gate of the transistor 21A. A second limit circuit 26 is connected to the gate of the transistor 21B.

[0027] The first limit circuit 25 and the second limit circuit 26 have the same circuit configuration, and the second limit circuit 26 is a redundant circuit of the first limit circuit 25. The temperature of the heater 12 detected by the first temperature sensor 14 is input to both circuits 25 and 26. Each of the circuits 25 and 26 compares the input temperature with a threshold value S2. Note that the threshold value S2 may be the same as the threshold value S1, or may be a different value (particularly, a value higher than the threshold value S1).

[0028] When the input temperature of the heater 12 is equal to or lower than the threshold value S2, that is, when the temperature of the heater 12 is within the normal range, the first limit circuit 25 supplies an on signal (e.g., a High signal) to the gate of the transistor 21A to turn on the transistor 21A. When the input temperature of the pressure sensor 11 exceeds the threshold value S2, that is, when the temperature of the heater 12 is higher than necessary, the first limit circuit 25 supplies an off signal to the gate of the transistor 21A to turn off the transistor 21A. When the transistor 21A is turned off, the power supply to the heater 12 is cut off and the heater 12 stops generating heat.

[0029] Similar to the first limit circuit 25, the second limit circuit 26 supplies an ON signal to the gate of the transistor 21B to turn on the transistor 21B when the input temperature of the heater 12 is equal to or lower than the threshold value S2. The second limit circuit 26 supplies an OFF signal to the gate of the transistor 21B to turn off the transistor 21B when the input temperature of the pressure sensor 11 exceeds the threshold value S2. When the transistor 21B is turned off, the current to the heater 12 is cut off and the heater 12 stops generating heat.

[0030] As described above, in the first embodiment, the temperature of the heater 12 is feedback-controlled by the control circuit 22 based on the temperature of the pressure sensor 11. When the temperature of the heater 12 detected by the first temperature sensor 14 becomes higher than the threshold value S1, the control circuit 22 turns off the transistor 21C to forcibly cut off the power supply to the heater 12. On the other hand, the redundant first and second limit circuits 25 and 26 also monitor the temperature of the heater 12 detected by the first temperature sensor 14 individually, and when the temperature of the heater 12 detected by the first temperature sensor 14 becomes higher than the threshold value S2, they turn off the transistor 21B or 21C. This also forcibly cuts off the power supply to the heater 12. With this configuration, even if one of the first and second limit circuits 25 and 26 fails and the limit function does not work, and the control circuit 22 goes out of control without the user noticing, the power supply to the heater 12 can be forcibly cut off by the other. As described above, according to the first embodiment, the likelihood that a limit circuit will remain that operates normally is higher than in the case where there is only one limit circuit without redundancy, and the heater 12 is prevented from becoming unnecessarily hot with a high degree of certainty.

[0031] Second embodiment Next, a vacuum gauge 50 according to a second embodiment of the present invention will be described with reference to Fig. 2. In the following description, differences from the first embodiment will be mainly described, and descriptions that overlap with the first embodiment will be omitted as appropriate. In particular, members or circuits that are the same as or similar to those in the first embodiment will be given the same reference numerals, and detailed descriptions will be omitted.

[0032] As shown in FIG. 2, the vacuum gauge 50 has a heater control device 60 instead of the heater control device 20 of the first embodiment. The heater control device 60 does not have the transistor 21C of the heater control device 20, but has a logic gate element 67 instead. The logic gate element 67 is an AND element here. The logic gate element 67 receives the above-mentioned on or off signal output from the control circuit 22 and the above-mentioned on or off signal output from the second limit circuit 26. The logic gate element 67 takes a logical product of these signals, and outputs an on or off signal indicating the result of the logical product to the transistor 21B. When on signals are input from both the control circuit 22 and the second limit circuit 26, the logic gate element 67 outputs an on signal to the transistor 21B. The logic gate element 67 outputs an off signal to the transistor 21B when an off signal is input from at least one of the control circuit 22 and the second limit circuit 26, that is, when an off signal by PID control is input from the control circuit 22, or when an off signal is input from the control circuit 22 or the second limit circuit 26 when the temperature of the heater 12 from the first temperature sensor 14 exceeds the threshold value S1 or S2. This cuts off the power supply to the heater 12.

[0033] With the above-described configuration, as in the first embodiment, the heater 12 is prevented from becoming too hot. Furthermore, in the second embodiment, the transistor 21C is eliminated compared to the first embodiment, and a logic gate element 67 is added instead. In general, logic gate elements such as AND elements are less expensive and less prone to failure than transistors (especially FETs). Therefore, the heater control device 60 of the second embodiment can be formed at a lower cost and has a lower failure rate for the entire heater control device compared to the heater control device 20 of the first embodiment.

[0034] (Modification) Various modifications may be made to the first and second embodiments. For example, the present invention may be applied to an apparatus that targets a heater of an apparatus other than a vacuum gauge. The first and second limit circuits 25 and 26 may each be configured to operate so as not to pass a current through the heater 12 when the temperature of the heater 12 detected by the first temperature sensor 14 exceeds a first threshold value. The control circuit 22 may be configured to control not to pass a current through the heater 12 when the temperature of the heater 12 detected by the first temperature sensor 14 exceeds a second threshold value (which may be the same as the first threshold value). The circuit configuration of each circuit configured in this manner is not limited to the above embodiments and may be arbitrary.

[0035] The transistors 21A to 21C may be replaced by various other switching elements such as bipolar transistors. Each of the switching elements may be, for example, an element disposed on the current path R1 of the heater current flowing through the heater 12, and switched to an OFF state in which no current flows through the current path R1 or the heater 12 based on a signal (such as an OFF signal) from the first limit circuit 25, the second limit circuit 26, the control circuit 22, or the logic gate element 67. The transistor 21B may be, for example, a switching element that switches to an OFF state in which no current flows through the current path R1 or the heater 12 when at least one of the signals from the control circuit 22 and the second limit circuit 26 is an OFF signal, as in the second embodiment. The logic gate element 67 may be, for example, an element that receives a signal from the control circuit 22 and a signal from the second limit circuit 26, and outputs an OFF signal to a switching element such as the transistor 21B when at least one of the signals is an OFF signal.

[0036] Although the present invention has been described above with reference to the embodiment and the modified examples, the present invention is not limited to the above embodiment and the modified examples. For example, the present invention includes various modifications to the above embodiment and the modified examples that can be understood by a person skilled in the art within the scope of the technical idea of ​​the present invention. The configurations listed in the above embodiment and the modified examples can be appropriately combined within a range without contradiction. [Explanation of symbols]

[0037] 10...vacuum gauge, 11...pressure sensor, 12...heater, 13...heater power supply circuit, 14...first temperature sensor, 15...second temperature sensor, 20...heater control device, 21A-21C...transistor, 22...control circuit, 23, 24...ADC, 25...first limit circuit, 26...second limit circuit, 50...vacuum gauge, 60...heater control device, 67...logic gate element, R1...current path.

Claims

1. A control circuit configured to control a temperature of a heater by controlling a current flowing through the heater which heats a heating target; a first limit circuit that operates to prevent the current from flowing through the heater when the temperature of the heater detected by a first temperature sensor exceeds a first threshold value; a second limit circuit which is a redundant version of the first limit circuit and operates to not allow the current to flow to the heater when the temperature detected by the first temperature sensor exceeds the first threshold value; The control circuit includes: feedback-controlling the current based on the temperature of the object to be heated detected by a second temperature sensor so that the temperature of the object to be heated becomes a target temperature; when the temperature detected by the first temperature sensor exceeds a second threshold value, a control is performed to prevent a current from flowing through the heater in priority to the feedback control of the current. Heater control device.

2. The first threshold is a value higher than the second threshold. The heater control device of claim 1 .

3. a first switching element that is provided on a current path of the current and that switches to an off state in which the current does not flow based on a signal output from the first limit circuit; a second switching element that is provided on the current path and is switched to an off state in which the current does not flow based on a signal output from the second limit circuit; a third switching element that is provided on the current path and is switched to an off state in which the current does not flow based on a signal output from the control circuit; The heater control device according to claim 1 or 2, further comprising:

4. a fourth switching element that is disposed on the current path and is switched to an off state in which no current flows through the current path based on an off signal from the first limit circuit; a fifth switching element that is disposed on the current path and that switches to an off state in which no current flows through the current path when at least one of the signal from the control circuit and the signal from the second limit circuit is an off signal; The heater control device according to claim 1 or 2, further comprising:

5. a logic gate element that outputs an OFF signal when at least one of the signal from the control circuit and the signal from the second limit circuit is an OFF signal; the fifth switching element is switched to the off state when the off signal is input from the logic gate element; The heater control device according to claim 4.

6. A heater control device according to any one of claims 1 to 5, The heater; a diaphragm-type pressure sensor heated by the heater; the control circuit controls the heat generation of the heater so that the temperature of the pressure sensor becomes a predetermined temperature. Vacuum gauge.

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