GB987279A - Gas discharge detection apparatus - Google Patents

Abstract

987,279. Leak detecting apparatus. VARIAN ASSOCIATES. Dec. 11, 1962 [Dec. 15, 1961], No. 46794/62. Heading G1N. A leak detector for a gas discharge device 13 operating at very low pressure within a vacuum tight envelope 14 to be monitored comprises a power supply 12 for the discharge device 13 means 75 (Fig.2) for providing a voltage proportional to the total current drawn by the device 13, means 154 to provide a variable voltage in opposition to the first voltage and means 16 for measuring the difference between the two voltages. In the embodiment shown in Fig. 1 the power supply 12 includes a constant voltage transformer 20 which is bypassed unless the current drawn by the discharge device 13 which is a sputter ion pump is below a certain value when relay 13 opens removing the current from relay 36 and connecting the primary winding of the transformer 34 to the secondary winding of the constant voltage transformer. The current passing through the sputter pump 13 produces a voltage across resistors 75 which is compared with the voltage produced on potentiometers 120, 123 by a long tailed pair 95, 96 giving an indication on meter 135. If an external record is required switch 103 alters the differential amplifier circuit and provides a signal at 145 which has one side earthed for use with external equipment. To operate the device switch 25 is depressed switching in relay 21 which is self holding, and switch 42 is closed short circuiting relay 58. As the sputter pump 13 reduces the pressure the current falls to a steady value which is so low that the constant voltage transformer 20 is switched into the power supply circuit. Switch 42 is now opened so that too large a current through resistor 55 switches relay 58 thus removing the power. Switch 74 is then adjusted to give an indication on meter 67 and then the D.C. voltage source provided by potentiometers 120 and 123 is adjusted in conjunction with sensitivity switch 129 to give a half scale reading on the sensitive meter 135. To test for leaks a gas is now sprayed on the discharge apparatus and any resultant change in equilibrium current is detected on meter 135. If two gases are used, say oxygen and argon, then deflections will occur in opposite directions further improving the sensitivity. It is stated that the detector is useful for the control of the manufacture of discharge devices. The connection of the point 51 to the core of transformer 34 is stated to reduce the effect of transformer leakage currents.