Monroe Electronics Electrostatic Voltmeter - Isoprobe® - model 279L - Manual (Page 10)

Page 7
SECTION 4
OPERATION
CAUTION:
Verify that instrument operating voltage matches local power line voltage. See Section 2 and Appendix II.
PRECAUTIONARY NOTE
Model 279 is a non-contacting voltmeter. The potential of the probe will attempt to follow the potential of any object
within the field of view of the sensitive electrode (up to
3400 volts) when the instrument is operating. In the interest
of operator safety and also to reduce high voltage stress within the instrument, it should be left in the STANDBY
mode whenever it is not being used and particularly when the probe will not be “looking” at a surface potential of
less than 3000V.
A. Initial setup:
As shipped from the factory, the instrument is set up to make general-purpose electrostatic measurements except
for zero adjustment.
1. Position probe approximately 1 /
8
” from a grounded surface.
2. Switch into OPERATE mode.
3. Adjust ZERO 1 for an indication of 0000 on meter.
4. Proceed with measurements.
B. Restoration of factory settings:
The following steps are necessary only if the factory settings of ZERO 2 and/or GAIN controls have been disturbed
as evidenced by a constant zero offset or unstable performance at close probe to surface spacing.
ZERO 2
1. With the probe positioned as above, switch into STANDBY mode.
2. Adjust ZERO 2 for an indication of 0000 with approximately 50% polarity indecision.
GAIN
This adjustment requires a metallic test surface at least 3- 4 inches (50-75mm) square and a means of applying
repetitive pulses or square waves to it. Amplitude should be in the order of 100-300 volts with a rise time
significantly better than 2 milliseconds. An oscilloscope is also required.
1. Set GAIN to maximum counterclockwise (CCW) rotation.
2. Position probe 0.005” (0.13mm) from the test surface.
3. Apply repetitive pulses to the test surface while observing the output of the 279.
4. Adjust GAIN for optimized transient response (fastest rise time with minimum overshoot and no oscillatory
tendency).