Frequently Asked Questions

Are the Trek bipolar high voltage amplifiers able to swing through a zero voltage level?

Yes, Trek's bipolar amplifiers, as well as most unipolar models, are able to swing through zero with virtual zero crossover distortion.

What causes triboelectric surface charging?

One of the major causes of triboelectric surface charging is when two unlike materials are rubbed against each other.  Depending on where these materials fall on the triboelectric series table, one material will tend to become more positively charged, while the other material becomes more negatively charged.

Is it possible for Trek's probes to be cleaned (probes used with a Trek electrostatic voltmeter)?

Yes.  The procedure for cleaning Trek's probes is:

  1. Turn off the electrostatic voltmeter and disconnect the probe.
  2. Pour a generous amount of isopropyl alcohol into the aperture of the probe and shake to dislodge any contaminants.
  3. Turn the probe so the aperture faces down and pour out the alcohol.
  4. Gently shake the probe to remove excess alcohol and allow to dry (at least 15 minutes) before placing probe back into service.
What is the difference between side view and end view probes? (probes used with a Trek electrostatic voltmeter)?

The primary difference between side view and end view probes is the orientation of the sensor aperture which needs to be facing the surface to be measured. On the side view probe, the sensor aperture is on the side of the probe thereby requiring the probe body to be parallel with the measured surface. On the end view probe the sensor aperture is on the end of the probe, requiring the probe body to be perpendicular with the surface being measured. Trek offers the different styles to provide our customers with the option which best meets their capability to mount the probes into the application area.

In relation to Trek non-contacting electrostatic voltmeter (ESVM) probes, what does the term “spot surface resolution” mean?

Spot surface resolution is the diameter of a spot on the surface which is actually being measured by the non-contacting ESVM probe. The diameter of the spot area being measured is largely influenced by the spacing between the probe and the surface being measured, as well as the probe’s aperture size.

As a general rule of thumb for Trek’s electrostatic voltmeters, the ratio is 5:1.  For example, using a standard Trek probe spaced at a distance of 2mm from the surface, the surface area being measured is a surface spot diameter of approximately 10mm. If the Trek probe-to-surface spacing is 3mm, the surface area diameter spot being measured is approximately 15mm. This ratio will vary somewhat between different models. Specific information for different probe models is available.

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What equipment can we use as an input signal for a Trek high voltage amplifier?

Trek’s high voltage amplifiers typically have a nominal input impedance in the range of 20 kΩ to 50 kΩ (depending on the model). Providing this high impedance input allows most commercial devices (i.e. low voltage signal sources, function generators, digital to analog converters, etc.) with output current capabilities in the order of 1mA to be used as the input driver for Trek’s high voltage amplifiers.

What types of materials are recommended for fixturing probes (probes used with a Trek electrostatic voltmeter)?

Trek recommends a charge non-retaining insulator such as phenolic or Bakelite® (resistance range 108 to 1011).

What are some examples of probe fixtures?

Trek square body probes used with Trek electrostatic voltmeters are available with an end view or side view sensor. Here are two diagrams showing how to fixture the probes. Also refer to ‘materials’ information above.

Trek Probe Fixture Examples

What is the issue with fieldmeters?

Fieldmeters are typically limited to large minimum probe-to-surface distance applications, therefore resulting in large spot resolution measurements and compromised accuracy. As all non-contacting measuring technologies measure the weighted-average of all charges contained within the resolution spot, the measurements obtained when using a fieldmeter (with its inherent large-area resolution) are particularly vulnerable to weighted-average measurement errors caused by mixed polarity charge located within the measured spot areas. In the extreme, equal and opposite values of even very high charges will result in a ‘zero’ reading by a fieldmeter.

Trek Electrostatic Voltmeters, such as Model 520 or Model 541A with their high resolution (small spot) capabilities, will provide higher accuracy readings by reducing the weighted-average measurement error effect.  In addition, fieldmeters are calibrated to be operated at a fixed probe-to-surface spacing and will experience large measurement errors when operated at other spacings (whether the difference is subtle or significant).

The Trek Model 520 and Model 541A use a technique which holds calibration relatively fixed over large spacing changes, allowing for high accuracy measurements regardless of changes in spacing (subtle or significant).

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