JPH01106210A - Emission controller - Google Patents

Abstract

PURPOSE:To improve responsiveness by comparing an emission current detecting value with a reference value and controlling the ON/OFF operation of filament current based on the compared output. CONSTITUTION:In the emission controller, a triode type ionization vacuum gauge 10 is constituted of a filament 11, a glid 12 and a collector 13. An ion current measuring circuit 14 is connected to the collector 13 in the vacuum gauge 10 and a constant voltage circuit 15 is connected to the glid 12. On the other hand, power is supplied from a power source 21 to the filament 11 through a power transistor (Tr) Q1 and a switch 22. Emission current is detected by a resistor R4. In addition, the controller is provided with a Schmitt circuit constituted of an operational amplifier 23, a reference voltage power supply 24, etc., a photocoupler 25 and an abnormality detecting circuit 26. Thus, the Tr Q1 can be previously prevented from being damaged due to the short of the filament circuit.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to an emission control device that controls the current (emission current) emitted from a thermionic emitter, and particularly utilizes ON/OFF of a filament current. The present invention relates to an emission control device that stabilizes emission current.

(Prior Art) Conventionally, in a triode type ionization vacuum gauge, electrons emitted from a filament are accelerated by the positive potential of a grid, gas is ionized by the accelerated electrons, and the ions are collected in a collector at a negative potential. The degree of vacuum is determined by aPI by utilizing the fact that the ion current flowing due to ionized gas molecules is proportional to the residual gas pressure in the vacuum.

In such an ionization vacuum gauge, if the emission current fluctuates, the ion current also fluctuates due to this fluctuation, making it impossible to accurately measure the degree of vacuum. In particular, the relationship between the current flowing to heat the filament and the emission current is exponential. Therefore, unless the filament current is stabilized, the emission current will fluctuate greatly due to disturbances such as power supply voltage fluctuations, making it impossible to use it as a measuring device. Therefore, an emission control device that stably controls the emission current is required.

A possible method for this type of device is to detect the emission current by detecting the voltage drop of a resistor, and feed this detected value back to the filament current via an operational amplifier, etc., but this method uses analog negative feedback control to prevent disturbances. It is controlled by averaging. In this case, the response is slow because the response to the disturbance is averaged, and overshoot occurs due to a large disturbance. Furthermore, since it is proportional control, there is a problem in that fluctuations occur on the order of several percent.

It is also conceivable to input the amplifier output to a switching regulator to control the ON/OFF current flowing through the filament (variable pulse width according to the amplifier output: PWM control). However, although this method can reduce the response time, it still cannot solve the overshoot problem. Furthermore, a complicated circuit such as a switching regulator for PWM control is required, resulting in a problem that the overall configuration becomes complicated.

On the other hand, when controlling the filament current ON/OFF,
It is necessary to detect abnormalities such as short-circuits or opens in the filament or grid circuits. In particular, a short circuit in the filament will lead to the destruction of the power transistor connected to the filament energizing circuit, and an open grid circuit will cause power to be directly input to the filament, resulting in a shortened filament life (these abnormalities can be detected). To do this, detectors may be provided in each part, but the number of detectors increases and the configuration becomes complicated.

There is also a method of connecting a low resistance for current detection in series with the above transistor in order to detect a short circuit of the filament, but in this case, the resistance itself becomes a source of loss, which is not desirable. Particularly in small voltage, large current circuits such as filament current-carrying circuits, inserting a current detection resistor results in a large loss.

(Problems to be solved by the invention) Conventionally, it is necessary to stabilize the emission current in ionization vacuum gauges, but current emission control devices have problems such as slow response to disturbances and overshoot. was there.

Furthermore, it is necessary to detect abnormalities in filament circuits, grid circuits, etc., but providing an abnormality sensor for each circuit poses problems such as complicating the overall configuration.

Furthermore, the above-mentioned problem is not limited to ionization vacuum gauges, but also applies to those that emit electrons by heating a filament and require stabilization of the emission current.

The present invention has been made in consideration of the above circumstances, and its purpose is to be able to control the emission current with good responsiveness to disturbances without causing overshoot, and to stabilize the emission current. It is an object of the present invention to provide an emission control device that can be measured and that can detect abnormalities in each part with a single abnormality detection circuit.

(Means for Solving the Problems) The gist of the present invention is to stabilize the emission current by utilizing the lag in the thermal response of the filament.

That is, the present invention provides an emission control device that controls the emission current from the filament or the cathode heated by the filament to a desired value by varying the current flowing through the filament used for thermionic emission. The current detection circuit detects, and the detected value detected by this detection circuit is compared with a preset reference value, and when the detected value exceeds the upper limit of the reference value, the first
a comparator circuit that outputs a level signal and outputs a second level signal when the detected value exceeds the lower limit of the reference value, and energization of the filament when the comparison output is at the first level according to the output of this comparator circuit. a switching circuit that turns off the current and turns on the current flowing to the filament when the comparison output is at a second level; and a switching circuit that turns on the current flowing to the filament when the comparison output is at a second level, and a comparison output of the comparison circuit that repeats the first and second levels or remains at the second level. An abnormality detection circuit is provided for detecting an abnormality by determining whether the abnormality is present.

(Function) According to the present invention, since the detected value is compared with the reference value and the filament current is controlled to be ON/OFF depending on the magnitude of the detected value, the response characteristics to disturbance can be made extremely fast. Furthermore, since the emission current can be suppressed between the upper limit and the lower limit of the comparison level by the comparison circuit, overshoot can be reliably prevented.

Further, by providing only a single abnormality detection circuit, abnormalities in each part can be detected, and it is possible to prevent the overall configuration from becoming complicated due to abnormality detection.

In addition, when measuring the thermal delay of the filament, it is several tens of I
It is the time constant of Ilsec. Therefore, instead of continuous control,
Considering the case where the filament current is directly switched, switching at 20 KHz or higher is required to sufficiently reduce the ripple of the emission current. Additionally, to maximize control response speed, ripple can be used as is for judgment.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a schematic configuration diagram showing an emission control device according to an embodiment of the present invention. In the figure, 10 is a triode type ionization vacuum gauge, and filament 11. grid 1
2 and a collector 13. This vacuum gauge 1
An ion current measuring circuit 14 is connected to the collector 13 of 0, and a grid constant voltage circuit 15 for applying a positive voltage is connected to the grid 12. The filament 11 of the vacuum gauge 10 receives a current from the filament power supply 21 as FE.
A switching power transistor Q consisting of T, etc.
and is supplied via switch 22. Here, the power supply 21 steps down and rectifies a commercial AC voltage to obtain a DC output at a low voltage v1.

Resistors R1*R2 are connected in parallel to the filament 13, and the connection point of these resistors R1 and R2 is the resistor R3.
r Grounded through R4 in series. The emission current is then converted into a voltage and detected by the resistor R4. Here, the resistors RInR2 have exactly the same resistance value, and by taking a midpoint voltage, voltage noise caused by switching of the transistor Q1 is prevented from affecting the measurement of the emission current. The resistor R3 is a bias resistor for the filament 11, and is determined based on the operating specifications of the ion gauge.

The connection point between the resistors R3 and R4 is connected to the non-inverting input terminal of the operational amplifier 23 via the resistor R5.

The inverting input terminal of the operational amplifier 14 is connected to the reference voltage power supply 24, and a resistor Rb and a capacitor C1 are respectively connected between the non-inverting input terminal and the output terminal, thereby forming a Schmitt circuit (comparison circuit). There is. The voltage Ve detected by the resistor R4 is compared with the reference voltage v2 by the comparison circuit, and when the detected voltage Ve is larger than the reference voltage (the upper limit of the reference voltage 2), the comparison circuit sends an "H" level signal. is output, and when the detected voltage ve is smaller than the reference voltage (lower limit of the reference voltage V2), an "L" level signal is output. Here, resistance R5+
R6 is a positive feedback resistor of the comparator circuit, which determines the upper and lower limits of the emission current. Capacitor C1 is intended to speed up the operation speed of the comparator circuit.

A resistor R7 and a photocoupler 25 are connected to the output end of the comparison circuit.
A power supply voltage vcc is supplied through a light emitting element (for example, a light emitting diode) Dl, and an abnormality detection circuit 26, which will be described later, is connected. The light receiving element of the photocoupler 25 (
For example, a phototransistor (phototransistor) D2 is connected between the gate of the power transistor Q1 and the terminal terminal of the filament power supply 21, and a resistor R8 is connected between the source and gate of Ql. The transistor Ql is turned on and off depending on the comparison output of the comparison circuit.

On the other hand, the abnormality detection circuit 26 is constructed as shown in FIG. That is, the output terminal 32 of the operational amplifier 23 is connected to the inverting input terminal of the operational amplifier 31 via the resistor R1, and the resistor R11 is connected to the resistor R1□ and the diode D1.
series circuits are connected in parallel. Furthermore, the inverting input terminal of the operational amplifier 31 is connected to the power supply V via a capacitor C11.
cc, and its non-inverting input terminal is connected to the power supply Vcc via a resistor R13 and to a ground terminal via a resistor R14. Then, the output terminal 3 of the operational amplifier 31
3 is connected to a relay (not shown), etc., and the switch 22
It is designed to turn on and off.

Next, the operation of this apparatus configured as described above will be explained.

First, the emission current is small and the voltage across resistor R4 (
When the detection voltage (detection voltage) Ve is lower than the reference voltage v2, that is, during the period (■) in FIG. Become. That is, current is supplied to the filament 11, and the filament temperature gradually increases.

During the period (2), the upper limit level is when the voltage V' at the non-inverting input terminal of the operational amplifier 23 becomes higher than the reference voltage v2, and the output of the comparator circuit is "L", so V' mVe Skewer R6 / (R5+R6) is the reference voltage v
It is time to exceed 2. Therefore, when the detection voltage Ve, which is the voltage across resistor R4, becomes higher than V2・(Rs +R6)/R6, that is, when the detection voltage Ve is higher than the reference voltage V2, v2・(R5
/R6), the output of the comparison circuit becomes "H" level. Then, during the period ■ when the comparison output becomes “H#”, transistor D2 is OFF, and transistor Q
1 is also turned off, and the current supply to the filament 11 is stopped.

In the period (2), the lower limit level is when the voltage V' at the non-inverting input terminal of the operational amplifier 23 becomes lower than the reference voltage v2, and the output of the comparator circuit is "H", so V' -Vcc- (Vcc-Ve)・R6/(R5+R
6) exceeds the reference voltage v2 to one side. Therefore, the detection voltage Ve, which is the voltage across the resistor R4, is V2- (
Vcc V2 ) ・When it becomes smaller than (R5/R6), that is, when it becomes smaller than the reference voltage v2 (Vcc - V2)
- When the voltage decreases by (R5/R6), the output of the comparator circuit becomes "L" level. Then, during the period (2) in which the comparison output becomes "L", the transistor D2 is turned on, the transistor Q1 is turned on, and the filament 11 is heated by electricity again. By repeating this operation, the filament current turns ON.
- OFF control is performed, and the emission current changes between the upper and lower limits of the reference value.

Therefore, if R6) and R5 are set, both the upper and lower limits will be extremely close to the reference voltage v2, the width of the upper and lower limits will be sufficiently small compared to the reference voltage, and the emission current will be stably maintained within an extremely small range. That will happen. And in this case,
Since the emission current is always stable within a very small range between the upper and lower limits of the reference value, overshoot as shown at A in FIG. 4 does not occur. On the other hand, in proportional control, overshoot occurs as shown at B in FIG. Further, since the ON/OFF control is performed not by proportional control but by the binary output of the comparator circuit, control can be performed with good responsiveness to power supply voltage fluctuations, etc.

By the way, if an abnormality occurs in the oven of the filament circuit, a short circuit, or an oven of the grid circuit in the above-mentioned device, it is undesirable because it may destroy the transistor Q1 or shorten the life of the filament.

Therefore, in this embodiment, the abnormality is detected by the abnormality detection circuit 26.

That is, the output of the comparator circuit remains at the "L" level in response to the above abnormality. In this case, in the abnormality detection circuit of FIG. 2, since the input terminal 32 remains "L", the capacitor C11 is charged, and the voltage at the inverting input terminal of the operational amplifier 31 becomes lower than that at the non-inverting input terminal. Then, the output of the operational amplifier 31 changes from "L" to "H" level. If there is no abnormality mentioned above, the comparator circuit repeats "L" and "H", so the input terminal 32 also repeats "L" and "H", and the capacitor C1□ will not be completely charged. , the output of the operational amplifier 31 remains at "L". Therefore, depending on the output appearing at the output terminal 33, the switch 22
By driving the filament ON and OFF (i. turning the switch 22 OFF when the force end 33 becomes "H"), it is possible to quickly stop the energization of the filament in the event that an abnormality occurs.

Thereby, it is possible to prevent the failure of the transistor Q1 due to a short circuit in the filament circuit, and it is also possible to prevent the life of the filament 11 from being shortened due to the oven of the grid circuit. Further, unlike the case where abnormality sensors are provided at multiple locations, it is sufficient to provide an abnormality detection circuit at one location, so it is possible to minimize the complexity of the configuration.

Thus, according to this embodiment, it is possible to control the filament current with good responsiveness to disturbances such as fluctuations in the power supply voltage, and moreover, it is possible to prevent the occurrence of overshoot. In addition, the circuit configuration is simple, and since ON/OFF control is performed by switching, there is little circuit loss. The switching frequency is determined by the Schmitt width and the response speed of the filament, so changing the filament does not affect the response of the circuit (matching is automatically achieved).

Therefore, it is extremely effective in stabilizing the emission current in the ionization vacuum gauge, and can contribute to improving the accuracy of measuring the degree of vacuum.

Further, abnormalities in the filament circuit or grid circuit can be detected by the single abnormality detection circuit 26, and when such an abnormality occurs, the energization of the filament can be stopped. Therefore, it is possible to prevent the life of the filament 11 from decreasing and the transistor Q1 from being destroyed.

Note that the present invention is not limited to the embodiments described above. For example, the emission current detection circuit is not limited to one that utilizes the voltage drop across the resistor R4, and may also directly input the emission current to the comparison circuit. In addition, the comparison circuit is not limited to one consisting of an operational amplifier, resistors R5, R6, capacitor 01, etc., and also compares the detected value with a reference value, and when the detected value exceeds the upper limit of the reference value to the + side, and when the lower limit is It is sufficient as long as the output is inverted when it crosses over to the side. Furthermore, switching circuits are not limited to FETs,
It can be changed as appropriate depending on the specifications.

Further, the photocoupler is not necessarily necessary, and the switching circuit may be directly controlled by the output of the comparison circuit.

Furthermore, in the embodiment, an ionization vacuum gauge has been described, but the present invention is applicable to devices that emit electrons by heating a filament and require stabilization of the emission current, such as an electron beam. It can be applied to an electron emission source in Lvi welding, electron beam welding, etc., and has an ET function.

Furthermore, the present invention is not limited to one in which electrons are directly emitted from a filament, but can also be applied to one in which electrons are emitted from a cathode heated by a filament. In addition, various modifications can be made without departing from the gist of the present invention.

(Effects of the Invention) As described in detail above, according to the present invention, the detected value of the emission current is compared with the reference value, and the filament current is controlled 0N-OFF based on the comparison output (binary signal). Therefore, the emission current can be controlled with good responsiveness to disturbances without causing overshoot. Moreover, since abnormalities are detected based on the output of the comparison circuit, abnormalities in each part can be detected with a single abnormality detection circuit, and the overall configuration can be prevented from becoming complicated due to abnormality detection. can. Therefore, it can be applied to devices that require stabilization of emission current by emitting electrons by heating the filament, and a great effect can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an emission control device according to an embodiment of the present invention, FIG. 2 is a circuit configuration diagram showing a specific configuration of an abnormality detection circuit used in the above device, and FIGS. 3 and 4 are schematic diagrams for explaining the operation of the above-mentioned device. 10... Ionization vacuum gauge, 11... Filament, 12
...Grid, 13...Collector, 14...Ion current measurement circuit, 15...Grid constant voltage circuit, 21
... filament power supply, 22... switch, 23.
31... operational amplifier, 24... reference voltage power supply, 25
...Photocoupler, 26...Abnormality detection circuit, Q...
・Transistor, R...resistance, C...capacitor. Applicant's agent Patent attorney Takehiko Suzue

Claims (6)

[Claims] (1) In an emission control device that controls the emission current from the filament or the cathode heated by the filament to a desired value by varying the current flowing through the filament used for thermionic emission, the emission current is detected. A current detection circuit compares the detected value detected by this detection circuit with a preset reference value, and outputs a first level signal when the detected value exceeds the upper limit of the reference value, and outputs a first level signal when the detected value exceeds the upper limit of the reference value. When the lower limit of the value is exceeded, the second
A comparison circuit that outputs a level signal, and switching that turns off the current flowing to the filament when the comparison output of the comparison circuit is at a first level, and turns on the current flowing to the filament when the comparison output is at a second level. and an abnormality detection circuit that detects an abnormality by determining whether the comparison output of the comparison circuit repeats the first and second levels or remains at the second level. Emission control device. (2) The current detection circuit is comprised of a resistor connected in series to a circuit through which an emission current flows, and outputs a voltage according to the magnitude of the emission current. Emission control device as described in section. (3) The comparison circuit includes an operational amplifier whose inverting input terminal is connected to a reference voltage power supply, a first resistor connected between the non-inverting input terminal of the operational amplifier and the output terminal of the current detection circuit, and an operational amplifier. 2. The emission control device according to claim 1, further comprising a second resistor connected between a non-inverting input terminal and an output terminal of the amplifier. (4) The emission control device according to claim 3, characterized in that a capacitor is connected in parallel to the second resistor of the comparison circuit. (5) The switching circuit is characterized by comprising a power FET inserted into the current-carrying circuit of the filament, and a photocoupler connected between the gate of this FET and the output end of the comparison circuit. An emission control device according to claim 1. (6) The abnormality detection circuit includes an integrator that integrates the comparison output of the comparison circuit, and a comparator that compares the integrated output of this integrator with a predetermined level, and the comparison output is connected to the first and second 2. The emission control device according to claim 1, wherein the emission control device outputs different levels when repeating the level and when remaining at the second level.