Products > Electrostatic Voltmeters > Non-Contacting

Model 323 High-Sensitivity, DC Stable ESVM

The Trek Model 323 Electrostatic Voltmeter performs highly sensitive voltage measurements using a variety of Trek side view probes with various body types (round, square).

The Model 323 is a versatile instrument used for a variety of electrostatic applications including materials evaluation, electret studies, charge accumulation on disk drive assemblies, and other extremely sensitive ESD sensitive components.

The Model 323 is specifically designed for high sensitivity applications and performs highly accurate, noncontacting measurement of electrostatic potentials of 0 to 100 V over a wide range of probe-to-surface distances.

The Model 323 has adjustments to compensate for many sensitive testing conditions. The response Speed control adjusts the speed/noise tradeoff of the AC response. The Drift/Spacing Null Adjustment minimizes the variation in zero offset voltage 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 scale of 10:1 or 20:1 voltage monitor output.

Trek patented low impedance probes assure measurement accuracy essentially independent of probe-to-test-surface spacing, humidity conditions, and contamination such as airborne dust, toner, ions and chemicals.

EPA Regulation 40 C.F.R. 86.1312-2007

The Model 323 meets the requirements described for an electrostatic monitor under the Environmental Protection Agency (EPA); Title 40 Part 86 – Control of Emissions from New and In-Use Highway Vehicles and Engines. Specifically 40 C.F.R. 86.1312-2007 - Filter stabilization and microbalance workstation environmental conditions, microbalance specifications, and particulate matter filter handling and weighing procedures.

This EPA regulation for emission control describes the procedure for measuring particulates from vehicle emissions that are accumulated on a filter for weighing. During the weighing process static neutralizers such as Po-210 sources are used to neutralize any charge build up on the filter that could interfere with the filter weighing. To insure the Po-210 sources (or other static neutralizers) are operating properly a static monitor is used to measure residual charge on the filter before weighing. Static charge on the filter needs to be less than ±2V DC which requires the use of a static measuring device having sufficient low voltage resolution, low zero offset, and good sensitivity. The Model 323 with 0.01V of resolution and 5mV of sensitivity meets these requirements to insure accurate and repeatable measurements required by EPA regulation 40 C.F.R. 86.1312-2007.

Show/Hide Product Technical Information


All specifications are with a Model 6000B-8 probe with a probe-to-surface separation of 1 mm.

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

5 mV.

DC Accuracy

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

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

Drift with Time
Less than 50 mV/hour, noncumulative.
1:1 monitor output Drift with Temperature
Less than 10 mV/°C.
10:1 or 20:1 monitor output Drift with Temperature
Less than 5 mV/°C..


Probe-to-Surface Separation
1 mm to 3 mm.

Standard Resolution Probes:

Model 6000B-8
Side-viewing, round body.

Model 6000B-16
Side-viewing, square body.



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 323 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
±2 counts, referred to the voltage monitor.
Sampling Rate
3 readings per second.

Drift/Spacing Null Adjustment
A back panel adjustment used to minimize 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 20 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 (10:1 or 20:1 ratio)
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.


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).

Power Consumption
12 VA, maximum.  

Ground Receptacle
Banana jack.

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

Operating Conditions
5 °C to 40 °C.
Relative Humidity
To 85%, noncondensing.

108 mm H x 223 mm W x 380 mm D
(4.25" H x 8.75" W x 15" D).

3.6 kg (8 lb).

Voltage Monitor Connector
BNC coaxial connector.


TREK, INC. certifies that each Model 323 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.



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