1-1. GENERAL. The Model 640 Vibrating Capacitor Electrometer
i3 an ultra-stable, solid-state microvolt electrometer.
a. As a Microvoltmeter. When used as a microvoltmeter, the
Model 640 has an input resistance greater than 1016 ohms
with thirteen ranges from 30 microvolts full scale to 30 volts.
b. As a Picoammeter. When used with the built-in,
high-megohm SHUNT RESISTORS, the instrument has twenty two
ranges from 10“^ ampere full scale to 3 x 10"-* ampere.
c. As a Coulombmeter. By switching an accurate guarded
capacitor in the feedback loop the instrument is useful as a
coulombmeter or current integrating amplifier. In the
CURRENT INTEGRATE mode the instrument has ten ranges from 2
x 10? coulomb full scale to 6 x 10? coulomb,
d. As an Amplifier. The analog OUTPUT permits use of the
instrument as a very stable, variable gain amplifier.
a. Excellent Stability. A stability specified at better than
5 x 10? ampere/day is useful for mass spectrometer,
resistivity, and ion chamber measurements .
b. Remote Input Head. A compact Remote Input preamplifier
permits convenient set up of an experiment.
c. High Input Impedance. Guarding plus the use of sapphire
insulation provides an input resistance greater than 10^
ohms shunted by less than 2 picofarads .
d. Battery or Line Operation. A choice of battery or line
operation permits complete isolation (in battery mode) from
power line when required.
e. Built-In Shunt'Resistors. Four high-megohm shunt
resistors can be switch selected (Input Head) for shunt or
feedback current measurements.