JP7640287B2 - Heater control device and vacuum gauge - Google Patents

Description

The present invention relates to a heater control device and a vacuum gauge.

As disclosed in Patent Document 1, a vacuum gauge having a pressure sensor may have a heater that surrounds the outer periphery of the pressure sensor. This heater is controlled by a heater control unit provided in the vacuum gauge, and by heating the inside of the pressure sensor (self-heating), the temperature around the diaphragm in the pressure sensor is kept high enough to prevent the precipitation of contaminants.

JP 2019-7906 A

The heater control unit controls the heat generated by the heater, but if the heater control unit goes out of control and is no longer able 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 has become higher than a specified temperature. However, if the vacuum gauge is used in a state where a malfunction has occurred in the limit circuit without noticing this, there is a risk that the limit circuit will not operate when the heater control unit goes out of control, causing the heater to become higher than necessary. This is also true of heaters in general.

The objective of the present invention is to prevent the heater from becoming too hot with a high degree of accuracy.

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

The control circuit may be configured to control so that no current flows through the heater when the temperature detected by the first temperature sensor exceeds a second threshold.

The heater control device may further include a first switching element provided on the current path of the current and switched to an off state in which 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 in which 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 in which the current does not flow based on a signal output by the control circuit.

The heater control device may further include a fourth switching element that is arranged on the current path and switches 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 that is arranged on the current path and 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 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.

To solve the above problem, the vacuum gauge according to the second aspect of the present invention comprises the heater control device described above, 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.

The present invention can prevent the heater from becoming too hot with high accuracy.

FIG. 1 is a block diagram showing the configuration of a vacuum gauge according to a first embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of a vacuum gauge according to a second embodiment of the present invention.

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.

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.

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 being measured by the displacement of a diaphragm. An example of the air pressure to be measured is the air pressure inside a vacuum chamber of a semiconductor manufacturing device.

The heater 12 heats the pressure sensor 11 by generating heat. 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 being measured (such as a vacuum chamber). The heater 12 is, for example, a band heater that includes a sheath heater. The heater 12 generates heat when a heater current supplied from the 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.

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.

The first temperature sensor 14 is provided at a predetermined location on 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. The first and second temperature sensors 14 and 15 each include an element such as a thermocouple or a thermistor that converts temperature into a voltage value, and detect and output the temperature by outputting a voltage value indicating the temperature.

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 26.

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

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 current path R1 of heater current flowing from heater power supply circuit 13 to the ground. Then, only when all transistors 21A to 21C are in the on state can heater current flow to heater 12, causing heater 12 to generate heat.

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 any type of logic circuit.

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, for example.

The ADC 24 is also connected to the control circuit 22. 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, the temperature of the heater 12 is higher than necessary, so 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 stops the heater 12 from generating heat.

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

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).

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 turns off, the current to the heater 12 is cut off and the heater 12 stops generating heat.

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

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 current 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 current 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 other can forcibly cut off the current to the heater 12. As described above, according to the first embodiment, there is a higher probability that a limit circuit that operates normally will remain than if there was only one limit circuit without redundancy, and the heater 12 is prevented from becoming too hot.

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.

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 that the heater control device 20 has, but instead has a logic gate element 67. 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 the 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 current to the heater 12.

As with the first embodiment, the above configuration highly reliably prevents the heater 12 from becoming too hot. Furthermore, in the second embodiment, compared to the first embodiment, the transistor 21C is eliminated, and instead a logic gate element 67 is added. 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 more inexpensively and has a lower failure rate for the entire heater control device than the heater control device 20 of the first embodiment.

(Modification)
Various modifications may be made to the first and second embodiments. For example, the present invention may be applied to a device that targets a heater of a device other than a vacuum gauge. The first and second limit circuits 25 and 26 may each be configured to operate so as not to allow a current to flow to 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 the current flowing through the heater 12 and to control so as not to allow a current to flow to 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 embodiment and may be arbitrary.

The transistors 21A to 21C can be changed to various other switching elements such as bipolar transistors. Each switching element 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.

Although the present invention has been described above with reference to the embodiments and modifications, the present invention is not limited to the above-mentioned embodiments and modifications. For example, the present invention includes various modifications to the above-mentioned embodiments and modifications that can be understood by a person skilled in the art within the scope of the technical concept of the present invention. The configurations listed in the above-mentioned embodiments and modifications can be combined as appropriate within a range that does not cause inconsistencies.

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 (6)

A control circuit configured to control a temperature of a heater by controlling a current flowing through the heater, the heater heating an object to be heated ;
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 prevent the current from flowing 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. The first threshold is higher than the second threshold.
The heater control device of claim 1 . 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: 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: 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. 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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