Electrostatic Testing & Consulting

Chilworth offers electrostatic testing for liquid conductivity test & more.

Liquid Conductivity Test
Liquid conductivity is defined as the reciprocal of the electrical resistance for a unit length and unit cross-sectional area through a liquid. It is the primary criterion for classifying liquids as low, moderately, or highly insulating. Insulating liquids have a propensity to generate and retain electrostatic charge and can produce hazardous electrostatic discharges when exposed to grounded plant, equipment, or personnel.

Chilworth Global measures liquid conductivity in accordance with British Standard 5958. The method involves pouring a liquid sample into a standardized electrode cell. A voltage is applied to the cell and the current through the cell is measured. Liquid conductivity is calculated using the known voltage, the measured current, and the geometrical relationship between the electrodes.

Measurement of Volume Resistivity and Charge Relaxation Time
- Powders and Dusts

Volume resistivity is a measure of the electrical resistance for a unit volume of material and is the primary criterion for classifying powders and dusts as low, moderately, or highly insulating. Insulating materials have a propensity to generate and retain electrostatic charge and can produce hazardous electrostatic discharges when exposed to grounded plant, equipment, or personnel.

In the absence of consensus U.S. standards, Chilworth Global measures volume resistivity in accordance with British Standard 5958. The method involves placing a powder or dust sample into a standardized electrode cell. A voltage is applied to the cell and the current through the cell is measured. Volume resistivity is calculated using the known voltage, the measured current, and the geometrical relationship between the electrodes.

The rate at which the charge on a material relaxes or decays provides another indication of its relative insulating or conductive character and serves as a useful companion measurement to volume resistivity. Charge relaxation rate is measured by placing a powder or dust sample in a test cell and charging the sample using a corona source. The cell is then grounded and the time required for the charge on the sample to relax to 1/e or 37 percent of its initial value is measured using a timer and an electrostatic fieldmeter.

Because of the effect of atmospheric and absorbed moisture on volume resistivity and charge relaxation rate, these tests are performed at ambient and low relative humidity conditions.

Measurement of Volume Resistivity and Charge Relaxation Rate
- Sheets, Films, Fabrics, Foils, and Coatings

Volume resistivity is a measurement of the electrical resistance for a unit volume of a material. The volume resistivity of a material can classify it as insulating, antistatic, or conductive.

Chilworth Global performs volume resistivity measurements for sheets, films, fabrics, foils, and coatings in general accordance with ASTM D257-93. The method involves placing a sample of the material between two electrodes of known geometry. A voltage is applied to one electrode, and the current through the material to the other electrode is measured. Volume resistivity is calculated using the known voltage, the measured current, the measured thickness of the sample, and the geometrical relationship between the electrodes.

The rate at which the charge on a material relaxes or decays provides another indication of its relative insulating or conducting character and serves as a useful companion measurement to volume resistivity. Charge relaxation rate is measured by placing a test sample in an electrode cell, and charging the sample with a corona source. The cell is then grounded and the time required for the charge on the sample to relax to 1/e or 37 percent of its initial value is measured using a timer and an electrostatic fieldmeter.

Because of the effect of atmospheric and absorbed moisture on volume resistivity and charge relaxation rate, these tests are performed at ambient and low relative humidity conditions.

Electrostatic Chargeability Test
The concept of chargeability refers to the propensity materials (solids and liquids) to become charged when flowing through conveyances or when handled in containers. Chargeability is measured by flowing samples through tubes of uniform length and made from different materials and measuring the resultant electrostatic charge. The test provides data which can be used to develop appropriate materials handling guidelines.

Because of the effect of atmospheric and absorbed moisture on the chargeability of some materials, this test is performed at ambient and low relative humidity conditions.

Electrostatic Discharge Testing
Insulating materials and conductive materials isolated from ground can become electrostatically charged. Accumulated charge can produce electrostatic discharges when exposed to ground. Electrostatic discharges from insulating materials are known as brush discharges, while discharges from isolated conductors are known as spark discharges.

The purpose of electrostatic discharge testing is to determine whether a material or object is capable of producing electrostatic discharges. Samples are electrostatically charged using a variety of methods and attempts to produce electrostatic discharges are made. Trials are performed under both ambient and low humidity conditions.

Measurement of Surface Resistivity and Charge Relaxation Time
- Sheets, Films, Fabrics, Foils, and Coatings

Surface resistivity is a measure of the electrical resistance for a unit area of material and is the primary criterion for classifying sheets, films, fabrics, foils, and coatings as low, moderately, or highly insulating. Insulating materials have a propensity to generate and retain electrostatic charge and can produce hazardous electrostatic discharges when exposed to grounded plant, equipment, or personnel.

Chilworth Global measures surface resistivity in accordance with ASTM D257-93. The method involves placing a concentric cylindrical electrode cell onto a sample material. A voltage is applied to the cell and the current across the sample surface is measured. Surface resistivity is calculated using the known voltage, the measured current, and the geometrical relationship between the electrodes.

The rate at which the charge on a material relaxes or decays provides another indication of its relative insulating or conductive character and serves as a useful companion measurement to surface resistivity. Charge relaxation rate is measured by placing a sample material into an electrode assembly and charging the sample using a corona source. The electrode assembly is then grounded and the time required for the charge on the sample to relax to 1/e or 37 percent of its initial value is measured using a timer and an electrostatic fieldmeter.

Because of the effect of atmospheric and absorbed moisture on surface resistivity and charge relaxation rate, these tests are performed at ambient and low relative humidity conditions

Propagating Brush Discharge Testing and Breakdown Voltage Measurement
- Sheets, Films, Fabrics, Foils, and Coatings

Propagating brush discharges are highly-energetic discharges capable of igniting many flammable atmospheres. These discharges derive their energy from the formation of a double layer charge on both sides of a surface. A double layer charge forms when the charge on one side of an insulating surface is sufficiently strong so as to induce an equal and opposite charge on the other side by atmospheric ionization. Propagating brush discharges occur when the double layer charge is exposed to grounded plant, equipment, or personnel.

Industrial equipment susceptible to propagating brush discharges include baghouse filters, flexible intermediate bulk containers, Teflon-lined piping, plastic liners, and steel vessels with synthetic coatings. Chilworth Global performs propagating brush discharge testing by placing a sample material upon a grounded metal plate and charging it using a corona source. Attempts are made to produce propagating brush discharges by approaching the charged material with a grounded spherical electrode.

Only materials possessing a certain dielectric strength are capable of supporting the double layer charge needed to produce propagating brush discharges. One measure of dielectric strength is breakdown voltage. Breakdown voltage refers to the point at which the insulating property of a material breaks down upon application of high voltage. Breakdown voltage is a useful measure for evaluating the propensity for a material to produce propagating brush discharges.

Chilworth Global determines breakdown voltage in accordance with DIN 53,481 (VDE 0303). The method involves placing a sample upon a grounded metal plate and then placing a cylindrical electrode connected to a high voltage power supply on top of the material. The voltage to the electrode is increased until the insulating property of the material breaks down and a large current passes through to the grounded metal plate.

Because atmospheric and absorbed moisture affects the propensity of a material to produce propagating brush discharges, these tests are performed at ambient and low relative humidity conditions.