GB1526059A - Electrometer - Google Patents

Abstract

1526059 Measuring electrostatic potential XEROX CORP 26 Nov 1975 [16 Dec 1974 (2)] 48596/75 Heading G1U An electrostatic potential measuring system incorporates a probe 30, as described in Specification 1483366, which is referred to, and a switch 24 by which either the probe sensor 28 can be connected as shown via a terminal A to a source follower 42 and a meter 66 to display the probe potential, or in order to zeroize the circuit and correct for any drift the probe sensor 28 can be grounded via one of three terminals C which are bridged by the switch, and simultaneously the potential across the meter is fedback via an integrator A2,80 and a resistor 82 and connected, together with ground, to the input of the source follower, whereby the potential across a bias capacitor 78 between the input to the source follower and a floating battery 59 is changed to bring the potential across the meter to zero. The circuit also includes an amplifier A1 which compares a fraction of the battery voltage from a potential divider 84,86 with the voltage across a Zener 74, so that, if with the switch in position C, the battery voltage is too low, a large positive voltage is produced by the amplifier A1 causing the meter to give a positive reading rather than a zero reading as it should when the zeroizing loop is operative.