An automatic apparatus for the testing of getter adsorption

Abstract

Routine testing of getter films has in the past been carried out using dosing methods, which require the constant attention of an operator. An apparatus has therefore been developed which operates automatically, recording the uptake of gas and at the same time maintaining the gas pressure over the getter constant. The principle of operation is as follows. Pulses of gas enter the getter chamber from a reservoir through a special magnetic valve which is continuously and rapidly opened and closed. The ratio of time open to time closed is automatically controlled so as to maintain a constant pressure in the getter chamber. Control is exerted by a special switching circuit which continuously varies the ratio of interval on to interval off, according to the input signal. This signal is provided by the voltage across the meter in the getter chamber Pirani gauge circuit. With a Pirani gauge attached to the gas reservoir, a continuous record of pressure drop against time can be obtained with a potentiometer recorder. If a capillary tube and high pressure Pirani gauge are interposed between the getter chamber and the magnetic valve, the signal from this Pirani gauge may be used to obtain a direct record of gettering rate against time. The apparatus has been used with carbon monoxide and hydrogen at getter chamber pressures of about 1μ. There is no limit with regard to the use of higher pressures, but with the present control circuit the use of lower pressures would lead to less satisfactory control, which at 1 micron pressure was never worse than ±10 per cent, and generally much better.