SU1413460A1 - Radio isotope ionization pressure gauge - Google Patents

Abstract

The invention relates to a technique for vacuum measurements, in particular, to pressure gauges based on ionizing probe chambers with an integrated source of radioactive radiation. The purpose of the invention is to increase the accuracy of gas pressure measurement with a change in ambient temperature. The ionization chamber 8 is connected at the output with an electrometric meter of ion current, and at the input with an adjustable source 7 of supply voltage. To compensate for the thermal drift of the output signal, a correction voltage driver 6 is connected to the power supply source 7, which, together with an electrometric ion current meter, heater 5, and thermal control circuit 3, is placed in a thermostat 2 on a common substrate with high thermal conductivity. The input of the heater 5 is connected to the output of the thermal control circuit 3 via the power amplifier 4. The effect of the emanometer is based on the ionization of the gas by radioactive radiation from the source of radioactive radiation placed in the ionization chamber 8. When the supply voltage is supplied to the input of the ionization chamber 8 from the source 7, a current signal proportional to the gas pressure is generated at the output of chamber 8. 4 il. (L

Description

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The invention relates to a vacuum measurement technique, in particular, to pressure gauges based on ionization chambers with a built-in radioactive source, and can be used to measure pressure and density of gases and vapors in vacuum installations, in process control devices and in metrology.

The aim of the invention is to increase the accuracy of gas pressure measurement with a change in ambient temperature.

Figure 1 shows the block diagram. the proposed pressure gauge; Fig. 3 shows the uncompensated residual thermal drift in Fig. 3 — the dependence of the current of the ionization chamber and the output signal of the pressure gauge on the supply voltage; ; Fig. 4 shows the control characteristic of the pressure gauge, i.e. the output signal of the correction voltage driver (curve A) and the resulting change in the voltage of the ionization chamber supply voltage as a function of temperature.

The pressure gauge consists (Fig. 1) of an electrometric current meter 1, thermostat 2, thermostat circuit 3, amplifier 4 M9, heater 5, former 6 Correction voltage, adjustable voltage source 7, ionization chamber 8 and gas sampler 9. The ionization chamber is located a collector, an anode and a source of radioactive radiation (not shown).

The ionization chamber 8 is connected by an opening through a gas collector 9 with an open gas space or atmosphere. Electrically, it is connected at the input to a source 7 of an adjustable voltage, and at the output to an input of an electrometric meter 1 of current. The thermal control circuit 3 is connected in series with the heater 5 via the power amplifier 4. The output voltage correction driver 6 is connected to the adjustable voltage source 7 and through it to the ionization chamber 8.

The electrometric current meter 1, the thermostat circuit 3, the heater 5 and the former 6 are located in the same thermostat 2 on a common subrun. When applied to the input of an ionized power voltage chamber for

its output generates a current signal proportional to the pressure of the gas.

The combination of these elements, connected in this way, allows, when the pressure gauge is operated, a change in the output signal due to the influence of temperature inconsistencies is compensated by the opposite change in the output signal due to the effect of voltage on the ionization chamber, which also changes as a result of these connections. temperaz: ury.

This happens in the following manner.

At a constant temperature, the voltage on the ionization chamber is constant. When measuring the ambient temperature, the temperature drift of the output signal occurs, i.e. an interference signal appears (Fig. 2). However, the output signal also depends on the voltage on the ionization chamber (Fig. 3). In order to change the effect of the interference signal (figure 2) by changing the voltage on the ionization chamber, the new elements introduced into the pressure gauge can provide both a decrease and an increase in the correction voltage, and the possibility of inversion, because the interference signal (figure 2) can have a different polarity. These functions are performed by the input correction voltage driver 6. Through the structural connection through the high thermal conductivity of the substrate of the thermostat 2 with the blocks 3 and 6 placed on it, the change in ambient temperature is adequate to the appearance at the input of the thermal drift signal 6. Shaper 6 of the correction voltage is built according to the analog voltage generator circuit of a special form (curve A in Fig. 4), which allows the input signal (Fig. 2) to be neutralized in the pressure gauge itself using an adjustable voltage source 7. The imaging unit 6 is a cascade of two amplifiers, structurally placed near the thermal control circuit 3. The first of these is an electrometric current meter, identical in circuit design and construction to an electrometric current meter 1. It is generated: t. the interference signal from the thermal drift (Fig. 2). is the same as the output of the meter 1, and thus plays the role of a dynamic memory for the analog voltage proportional to

error of the manometer from the thermal drift. In order to align this signal with the control characteristic of the source 7 of the regulated voltage (Fig. 4, curve A), the second part of the correction voltage generator 6, which is a voltage amplifier built on the operational amplifier d (OA) extremely small dependences of the output voltage drift on temperature and time, the low response of which does not impair the speed of the manometer. Amplifier It is equipped with a special adjusting resistor, by changing the coefficient The gain is adjusted so that at the output of the driver 6 the signal value is within the range of the adjustment characteristic of the source 7 of the regulated voltage, which the correction voltage signal will repeat. Thus, the correction voltage is generated (FIG. 4, curve BUT). It 25 is fed to the input of the source 7 of an adjustable voltage, at the output of which a floating operating voltage is formed (Fig. 4, curve B), which varies, for example, from 100 to 200 V, and the variation of which is compensated by the interference signal for residual thermodynamic field. Considering that the disturbance may vary in the area of both negative and positive voltages, the nominal operating voltage of the source 7

35

the gauge of standard products: radioactive source of type AIL RIG in, ionization chamber, operative amplifiers, K740UD4, 140UD13 in the correction voltage driver, transistors Shch972 and KT973 in the power amplifier. .

the adjustable voltage is set so that the operating point divides the output signal from the stringer voltage curve along the ordinate axis on Q two equal parts (point B in figure 3), for example 150 V.

In this case, the manometer allows, in a possible range of variation of the current of the ionization chamber, for example, from minus 5 3.5 -10 to plus 3.5 10 A, to compensate for the amplitude of the interference from minus 3.5 to plus 3.5 mV

The accuracy of the pressure measurement can be estimated by the formula

100D. t

and

cJ

(%);

at a temperature

inside the thermostat 50 ° C to within

.5-6 µV / S, which corresponds to the voltage increase of the correction voltage

where if is the relative error

D is the value of the temperature drift;

t is the temperature range of the medium;

and - output level. For the proposed manometer,

  0.06%.

when measuring the same pressure in the temperature range.

Claims (1)

Invention Formula A radioisotope ionization gauge containing an ionization chamber whose collector is connected to the input of an electrometric current meter, and the anode is connected to an adjustable power supply source, and a thermal control circuit, characterized in that, in order to increase the accuracy of measuring gas pressure when the surrounding temperature changes, however, no correction, an output connected to the input of an adjustable voltage supply source, as well as a heater, a power amplifier, and a thermostat, and heater turn connected to the output circuits of thermal control through the power amplifier and the electrometer measuring current, the heater, the thermal control circuit, and generates the measurement accuracy NIJ 25-30 times when used in the elements and nodes in a thermostat on a substrate with high thermal conductivity .. the gauge of standard products: radioactive source of type AIL RIG in, ionization chamber, operative amplifiers, K740UD4, 140UD13 in the correction voltage driver, transistors Shch972 and KT973 in the power amplifier. . The accuracy of the pressure measurement is estimated by the formula 100D. t and cJ (%); where if is the relative error D is the value of the temperature drift; t is the temperature range of the medium; and - output level. For the proposed manometer,   0.06%. when measuring the same pressure in the temperature range. Invention Formula A radioisotope ionization manometer containing an ionization chamber, the collector of which is connected to the input of an electrometric current meter, and the anode is connected to an adjustable source of supply voltage, and a thermal control circuit, in order to increase the accuracy of gas pressure measurement when the surrounding temperature changes, It has a correction voltage driver, an output connected to the input of an adjustable voltage supply source, and a heater, a power amplifier, and a thermostat, and the heater input is connected to the output of the thermal control circuit through a power amplifier, and the electrometric current meter, heater, thermal control circuit, and formi in a thermostat on a substrate with high thermal conductivity .. 3.5 3,5-tO-3, 5 - 3.5 to-3 Experience, naatafoui. Editor M.Kelemes Phi. one Compiled by And, Nevsky Tehred M. Khodanich Proofreader S. Cherni 200 pit iUioffainuv.f