Products > Electrostatic Voltmeters > Non-Contacting

Model 320C High-Sensitivity, DC Stable ESVM

The Trek Model 320C Electrostatic Voltmeter is a versatile instrument which is used for a variety of electrostatic applications including contact potential measurements, materials evaluation, and electret studies. The Model 320C makes highly accurate, noncontacting measurement of electrostatic potentials of 1 mV to 100 V over a wide range of probe-to-surface distances. The Model 320C is specifically designed for high sensitivity applications.

The Model 320C has adjustments to compensate for many sensitive testing conditions. A calibrated Null Voltage supply of ±10 volts nulls contact potentials when measuring voltages on dissimilar materials. The Null Voltage source may be used to null different work function voltages of the test surface or to function as a zero suppression voltage source. The response Speed Control adjusts the speed/noise tradeoff of the Model 320C AC response. The self locking Drift/Spacing Null Adjustment minimizes the variation in monitored voltage values as the probe to test surface spacing changes.

The front panel has an easy to read 3½ digit LED display. The detected output voltage can be monitored through a 1:1 voltage monitor output and a switch selectable ratio of 10:1 or 20:1 voltage monitor output.

The Trek patented low impedance probe assures measurement accuracy which is essentially independent of probe-to-test-surface spacing while eliminating the external environmental effects of high humidity and contamination, such as airborne dust, toner, ions and chemicals, on measurement accuracy.


Show/Hide Product Technical Information


Measurement Range
0 to ±100 V DC or peak AC.

1 mV.

Voltage Monitor Output
Better than ±0.05% of full scale.
Voltage Display
Better than or equal to ±2counts, referred to the voltage monitor.

Speed of Response (10% to 90%)
Less than 300 ms for a 100 V step.

Drift with Time

Less than 50 ppm/hour, noncumulative.
1:1 monitor output Drift with Temperature
Less than 50 ppm/°C.
10:1 or 20:1 monitor output Drift with Temperature
Less than 100 ppm/°C.


Null Voltage Source
A calibrated 10-turn dial representing a 10 volt supply, with switch selectable polarity, used to produce zero volts output when the probe is coupled to a known zero volt surface. Also used to null contact potentials on dissimilar surfaces.
±10 volts
20 mV.

Response Speed Control
A front panel potentiometer that adjusts the speed/noise tradeoff of the Model 320C AC response.




Voltage Display
3 1/2 digit LED display.
Switch selectable for ±10 V or ±100 V full scale.
Resolution 10 V Range
0.01 V.
Resolution 100 V Range
0.1 V.
Zero Offset
±1 count, referred to the voltage monitor.
Sampling Rate
3 readings per second.

Drift/Spacing Null Adjustment
This back panel adjustment minimizes the variation in monitored voltage values as the probe to test surface spacing changes.

Voltage Monitor Output (1:1 ratio)
A buffered 0 to ±100 V output providing a representation of the measured voltage.
1:1 of the measured voltage.
Output Noise
Less than 5 mV rms (measured using the true rms feature of the Hewlett Packard Model 34401A digital multimeter).
Output Current
5 mA.
Output Impedance
100 Ω, nominal.

Voltage Monitor Output
A buffered 0 to ±10 V output providing a representation of the measured voltage.
10:1 of the measured voltage or
20:1 of the measured voltage (switch selectable).
Output Current
5 mA.
Output Impedance
0.1 Ω, nominal.

Power Switch
A two position switch


Probe-to-Surface Separation (recommended)
±1 mm.

High Sensitivity Probe
Model 3250.





Accessories Supplied

  • Operator’s manual and line cord.


  • 344RA Full-Rack Mounting Kit (two instrument capacity)


Line Supply
Factory set for one of two ranges: 90 to 127 V AC or 180 to 250 V AC, at 48 to 63 Hz.
(Specify when ordering.)

Operating Conditions

0°C to 40°C.
Relative Humidity
To 90%, noncondensing.

108 mm H x 223 mm W x 370 mm D
(4.25" H x 8.75" W x 14.5" D).

3.6 kg (8 lb).

Voltage Monitor Connector
BNC coaxial connector.

Ground Receptacle
Banana jack.

AC Line Cord Receptacle
Standard three-prong line cord receptacle with integral fuse holder.


TREK, INC. certifies that each Model 320C is tested and calibrated to specifications using measurement equipment traceable to the National Institute of Standards and Technology or traceable to consensus standards. A Certificate of Calibration accompanies each instrument when it is shipped from the factory.
Low Voltage Safety Compliance
(EN 61010-1)
Overvoltage Category
CAT II: Local-level mains, appliances, portable equipment.
Pollution Category
Degree 1: Operate in environments where no pollution or only dry nonconductive pollution occurs.

All specifications are subject to change.

  • Products
  • Downloads
  • Technical Info
  • Applications
  • Sales & Support
  • News & Events
  • About Trek