Prostat CVM-780 - Theory of Operation; Notes & Cautions; III. Theory of Operation

6
Rev. D / January 2015
CVM-780 Contact Voltmeter
H. A small p replacement tool is supplied to prevent probe and
p damage when exchanging ps. The p should never be over
ghtened
I. An outer removable rubber boot reduces mechanical shock
during portable operaons and provides an easel stand during
use.
J. few alcohol prep wipes are included to periodically clean the
black insulator mounted at the front of the probe assembly. The wipe may be used to clean the
probe and instrument cases.  the alcohol wipes on the display LED.
III. 
The CVM-780 operaon is quite unique.
A. As the probe p of the CVM-780 approaches a charged conductor it senses the conductor’s
charge. The p is driven by the probe to match the conductor’s polarity and increases p voltage
as its distance to the conductor decreases.
B. While p voltage connues to increase as it approaches the charged conductor, the CVM-780
probe p does not reach the conductor’s full voltage unl it physically contacts the charged con-
ductor.
C. At the moment of contact a small transfer of electrons occurs from the conductor to the CVM-780
p that completes the measurement. The probe p voltage will be well within
1. 5% of the conductor’s original voltage, ±2 counts from ±25 to ±525 volts, and
2. Within 10% ±2 counts at <±25 volt measurements.
Therefore the change in conductor voltage at moment of p contact is very small.
D. Though very small electron transfer occurs at moment of contact, there is no measureable “ESD”
event when employing ceramic ps. The small amount of electron transfer is controlled by both p
and probe design. Also, there is no signicant RF generated because the electron transfer is small
and “relavely slow” to avoid a discharge event.
E. The resulng measurement accuracy depends on the actual voltage of the conductor, the length
and types of probe ps, and the inuences in the measurement environment. Environmental
inuences include presence and movement of objects and bodies, ambient condions, and size of
objects and their distance to ground (Capacitance).
IV. 
The CVM-780 is a precision instrument designed to measure electrostac DC voltage.