Products > Electrostatic Voltmeters > Non-Contacting

Model 370TR DC Stable Electrostatic Voltmeter

The Trek Model 370TR is a precision electrostatic voltmeter with the unique capability of making noncontacting surface voltage measurements in the range of 0 to ±3 kV DC or peak AC.

The 370TR employs an electrostatic field-nulling technique which achieves high DC stability and high measurement accuracy even if the probe to measured surface spacing changes. This permits measurements of either stationary or moving surfaces without the need to establish fixed spacing to maintain accuracy.

The Model 3629A Transparent probe permits light to pass through the probe to provide simultaneous radiation and measurement of a surface. This is useful for photosensitive surface studies such as ‘time of flight’ measurements of photoconductor surfaces.

A Digital Enable connection permits remote ON/OFF measurement capability. An automatic gain control feature of the 370TR eliminates the need for manual adjustment when changing probes or when changing the probe to measured surface separation. The 370TR also features one-step, push-button zeroing. When the ZERO button on the front panel is pressed, the 370TR automatically adjusts the output to zero volts when the probe is coupled to a known zero volt surface.

A precision voltage monitor provides a low-voltage replica of the measured electrostatic voltage for external monitoring purposes, or for use as a feedback signal in a closed-loop system.

An optional data acquisition module is available, featuring an IEEE-488 compatible interface, 14-bit resolution, 12-bit accuracy, and a programmable sampling period from 10 ms to 30 minutes

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All specifications are with a 3627 probe (standard) or 3629A probe (transparent ) with a probe-to-surface separation of 2 mm unless otherwise noted.

Measurement Range
0 to ±3 kV DC or peak AC

Measurement Accuracy
At the Voltage Monitor
Better than ±0.05% of full scale.

Measurement Accuracy
At the Voltage Display
Better than ±0.1% of full scale
±1 count, referred to the voltage
monitor. Note: The measurement
accuracy degrades to the larger of
±1.2% or 36 V in the presence of
line transients or RF fields up to
3 V/m.

Speed of Response (10%to 90%)
Less than 200 µs for a 1 kV step.

Drift with Time

Less than 150 ppm/hour, noncumulative.
Drift with Temperature
Less than 100 ppm/°C.

Data Acquisition Module (Optional)

Provides data output using an IEEE-488 compatible interface.
14 bit.
12 bit.
Sampling Period
Programmable from 10 µs to 30 minutes.
32 Kbytes (16 Kbytes of data words).
Acquisition Start Signal
External trigger or IEEE-488 Talk Enable or Group Trigger command.
Successive Data Acquisition
Internal timer or external trigger.
Interface Functions
SH1, AH1, T6, L4, SR1, RL1, PP0, DC1, DT0, C0, E2.
Switch selectable between 0 and 30.


Accessories Supplied

  • Operator’s manual, an IEC line cord for 90 to 127 V AC voltage source, or an unterminated power cord for a 180 to 250 AC line with the international color code as follows: brown-line, blue-neutral, and green/yellow-ground.



Zero Control
A momentary push-button switch to produce zero volts output when the probe is coupled to a known zero volt surface.

Automatic Gain
The Model 370TR automatically optimizes the AC response when changing the type of probe being used or when changing the probe-to-surface separation.

Voltage Monitor Output
A buffered output providing a low-voltage replica of the measured voltage.
1/100th of the measured voltage.
(1/200, 1/300, 1/600, 1/1000 options available.)
Offset Voltage
Less than 10 mV.
Output Noise
Less than 20 mV rms (measured using the true rms feature of the Hewlett Packard Model 34401A digital multimeter).
Output Impedance
Less than 0.1 Ω.
Output Current Limit
±10 mA.

Voltage Display
4-character, 7-segment LED display.
0 to ±3000 V.
1 V.
Zero Offset
±1 count, referred to the voltage monitor.
Sampling Rate
2.5 readings per second.

Digital Enable
An open collector, TTL compatible input to enable or disable the measurement. A TTL high (or open) will disable the measurement. A TTL low will enable the measurement


Probe-to-Surface Separation

2 mm ± 1 mm.

Model 3629A (Transparent)
Body Shape
Aperture Size
5.3 mm diameter.
Aperture Location
14.3 mm h x 21.9 mm w x 87.5 mm L


Model 3627
Body Shape
Aperture Size
1.5 mm x 3.0 mm.
Aperture Location
11.8 mm H x 11.1 mm W x 76.0 mm L


Power Requirements
Line Voltage
90 to 127 V AC 50 to 60 Hz.
(180 to 250 V AC, at 50 to 60 Hz optionally available).

Power Consumption
100 VA, maximum.

Operating Conditions

0°C to 40°C.
Relative Humidity
To 85%, noncondensing.

108 mm H x 223 mm W x 430 mm D
(4.25" H x 8.75" W x 17" D).

5 kg (11 lb).

Voltage Monitor Connector
BNC coaxial connector.

Digital Enable
BNC coaxial connector.

Ground Receptacle
Binding post.

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


TREK, INC. certifies that each Model 370TR 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.

All specifications are subject to change.


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