A comparative study of modulated Bayard Alpert gauges and an extractor gauge

Abstract

The experimental results obtained from two different modulated Bayard Alpert gauges and one extractor gauge are described. The ion-current pressure characteristics show that the two modulator gauges have a most probable error of ±50 per cent at a pressure of approximately 5×10 −11 torr. The extractor gauge showed a slow departure from linearity below 5×10 −10 torr, but the lower limit of pressure measurement could not be established as the system ultimate pressure was only 1×10 −11torr. The upper working pressure limits vary between 2×10 −6 and 1×10 −3 torr depending on the gauge. The sensitivity of the extractor gauge increased very considerably when the electron emission current rose above 10 −3A. A similar effect was observed, but to a much smaller extent, on the modulator gauges. The reverse x-ray current effect was shown to account for the premature fall off in linearity at low pressures of one of the modulated gauges when its bulb potential was the same as that of the ion collector.