NORME EUROPÉENNE English Version Electrostatics - Part 2-3: Methods of test for determining the resistance and resistivity of solid materials used to avoid electrostatic charge accumul
Instrumentation
General
The instrumentation may consist of either a DC power supply and an ammeter, or an integrated instrument (ohmmeter) National safety regulations shall be followed.
Instrumentation for laboratory evaluation
The output voltage under load shall be (100 ± 5) V for measurements of 1 × 10 6 Ω and higher, and (10,0 ± 0,5) V for less than 1 × 10 6 Ω
If an ohmmeter is used, readings shall be possible at least from 1 × 10 3 Ω to 1 × 10 13 Ω, with an accuracy of ±10 %
A DC power supply and ammeter can measure current ranging from 10 pA to 10 mA, with a combined accuracy of ±10%.
Instrumentation for acceptance testing
Instrumentation for laboratory evaluation or instrumentation meeting the following requirements shall be used for acceptance testing
The open circuit voltage shall be (100 ± 5) V for measurements of 1 × 10 6 Ω and higher, and (10,0 ± 0,5) V for less than 1 × 10 6 Ω
If an ohmmeter is used, readings shall be possible at least from 1 × 10 3 Ω to 1 × 10 13 Ω, with an accuracy of ±20 %
If a DC power supply and ammeter are used, readings shall be possible at least from 10 pA to 10 mA with an accuracy of ±20 %
In case of dispute, instrumentation for laboratory evaluations shall be used.
Instrumentation for compliance verification (periodic testing)
Instrumentation meeting the requirements for laboratory evaluations or acceptance testing, or instrumentation meeting the following requirements shall be used
Compliance verification instrumentation must measure accurately within a range that extends one order of magnitude above and below the intended measurement range The output voltage of this instrumentation may differ from that of laboratory evaluation or acceptance testing equipment, and it can be rated under load or in an open circuit To ensure consistency in measurement results, compliance verification instrumentation should be validated against laboratory evaluation or acceptance testing instruments.
In case of dispute, instrumentation for acceptance testing or laboratory evaluation shall be used.
Electrode assemblies
General
Electrodes must be made from a material that ensures close contact with the specimen surface while minimizing errors due to electrode resistance or contamination Additionally, the electrode material should be corrosion-resistant under testing conditions and must not react chemically with the specimen being tested.
The assemblies outlined in the following subclauses are recommended for use, although other configurations that meet national or international standards may also be acceptable For accurate volume resistance measurements of electrostatic dissipative materials, it is crucial that the guarded ring type probes have adequate spacing between the center (measuring) and ring (guard) contact electrodes to reduce stray currents that could distort the readings A minimum gap of 10 mm is advised In the event of any disputes, the assemblies specified in this standard should be utilized.
Assembly for the measurement of surface resistance
The electrode assembly, referred to as probe 1, features a central disc encircled by a concentric ring composed of conductive materials that establish contact with the test material The total mass of this electrode assembly is specified to be (2.5 ± 0.25) kg.
The contact surface material must exhibit a volume resistance of less than 10³ Ω when tested on a stainless, non-corrosive metal plate (excluding aluminum) as the counter electrode, using a voltage of (10.0 ± 0.5) V Additionally, it should have a Shore A hardness ranging from 50 to 70, as determined by ISO 7619-1 testing standards.
Insulating materials used in the electrode assembly shall have volume and/or surface resistance greater than 10 13 Ω when tested according to IEC 62631-3-1 and/or IEC 62631-3-2 respectively
The material under test shall be placed on an insulating support as described in 8.2.5
Figure 1 – Example of an assembly for the measurement of surface and volume resistance
Assembly for the measurement of volume resistance
The assembly features two electrodes positioned on opposite sides of the material being tested, as illustrated in Figure 4 The design of the top electrode assembly, referred to as probe 1, is detailed in section 8.2.2 and depicted in Figure 1.
The bottom electrode, referred to as probe 2, must be made of a durable, non-corrosive stainless steel plate, avoiding aluminum, and should be large enough to adequately support the specimen being tested Additionally, probe 2 should feature a permanent connecting terminal, such as a plug hole or riveted connector, and the use of crocodile clips is not permitted.
It should be placed either on an insulating support as described in 8.2.5 prior to test or be equipped with equivalent insulating feet.
Assembly for the measurement of resistance to ground/groundable
and point-to-point resistance
The electrode assembly features one or two electrodes, known as resistance to ground or point-to-point resistance, equipped with a conductive disk that contacts the test material (refer to Figure 2) The total mass of the electrode assembly is specified to be (2.5 ± 0.25) kg.
Insulator (> 10 13 Ω) Metal electrode mounting base
The contact surface material must exhibit sufficient conductivity, ensuring that two probes placed on a metal surface (e.g., probe 2) demonstrate a point-to-point resistance of less than 10³ Ω when tested with a voltage of (10.0 ± 0.5) V Additionally, the material should possess a Shore A hardness ranging from 50 to 70, as determined by ISO 7619-1 testing standards.
Insulating materials used in the electrode assembly shall have volume and/or surface resistance greater than 10 13 Ω when tested according to IEC 62631-3-1 and/or IEC 62631-3-2 respectively
The material under test shall be placed on an insulating support as described in 8.2.5
Figure 2 – Example of an assembly for the measurement of resistance to ground/groundable point and point-to-point resistance
Test support
The material must be evaluated on a smooth, flat surface with a surface resistance exceeding \$1 \times 10^{13} \, \Omega\$, as per IEC 62631-3-2 standards The testing surface should be at least 10 mm larger in both length and width than the specimen being tested, and the minimum thickness of the material should be 1 mm.
Sample preparation and handling
Refer to applicable material specifications for sampling instructions The specimens shall not be handled or marked in areas where measurements will be performed If the areas where
Insulator (> 10 13 Ω) Metal electrode mounting base
The test report must indicate any reworking of the electrodes in the instrumentation cable Surface resistance measurements should only be conducted without cleaning the surface if previously agreed upon or specified It is essential to handle and mount the specimens carefully to avoid contamination that could create electrical paths and negatively impact the test results.
Specimens shall preferably have a simple geometric shape in the form of sheets with a minimum size of at least 80 mm × 120 mm or 110 mm diameter
In the absence of specific regulations, at least three representative specimens of the sample material must be prepared, and the surface designated for testing should be clearly marked or identified.
Test procedures
Surface resistance measurements
The electrode assembly outlined in section 8.2.2 is linked to the instrumentation (refer to Figure 3) The specimen must be positioned on the test support with the testing surface facing upwards Subsequently, the electrode assembly should be placed at the approximate center of the specimen, ensuring it is at least 10 mm away from the edges.
Figure 3 – Basic connections of the electrodes for surface resistance measurements
Energize the instrumentation at a voltage of (10.0 ± 0.5) V and take the reading after (15 ± 1) seconds, unless otherwise noted If the resistance is below 1.0 × 10^6 Ω, document the value and move on to the next specimen If the resistance is equal to or exceeds 1.0 × 10^6 Ω, de-energize the instrumentation and repeat the process at (100 ± 5) V, recording the resistance after the specified electrification period.
Volume resistance measurements
The electrode assemblies outlined in section 8.2.2 are linked to the instrumentation, as illustrated in Figure 4 Initially, the bottom electrode (probe 2) is positioned on the test support, followed by placing the specimen on top Subsequently, the top electrode (probe 1) is carefully positioned at the center of the specimen, ensuring it is at least 10 mm away from the edges.
Figure 4 – Basic connections of the electrodes for volume resistance measurements
Energize the instrumentation at a voltage of (10.0 ± 0.5) V and take the reading after (15 ± 1) seconds, unless otherwise specified If the resistance is below 1.0 × 10^6 Ω, note the value and move on to the next specimen If the resistance is equal to or exceeds 1.0 × 10^6 Ω, de-energize the instrumentation and repeat the process at (100 ± 5) V, recording the resistance after the specified electrification period.
To evaluate the volume resistivity, it is essential to first determine the average thickness \( h \) of each specimen, adhering to the guidelines outlined in the applicable product specification before conducting any measurements.
Resistance to groundable point measurements
The test specimens must include a representative groundable point and should be positioned on the test support with the testing surface facing upward The electrode assembly (probe 3) should be placed on the specimen's surface, ensuring that its center is at least 50 mm from the edges or the groundable point (refer to Figure 5) Connect one lead of the instrumentation to the electrode assembly and the other lead to the groundable point.
Energize the instrumentation at (10,0 ± 0,5) V and record the reading after (15 ± 1) s if the indicated resistance is less than 1,0 × 10 6 Ω Then proceed to the next position or specimen
If the indicated resistance is equal or higher than 1,0 × 10 6 Ω, de-energize the instrumentation and repeat the procedure using (100 ± 5) V
Figure 5 – Principle of resistance to groundable point measurements
Put the electrode assembly (probe 3) onto the surface of the specimen in a position at least
50 mm away from the specimen edges or groundable point (see Figure 5) Connect the electrode assembly to one lead of the instrumentation and the groundable point to the other lead
Energize the instrumentation at (10,0 ± 0,5) V and record the reading after (15 ± 1) s if the indicated resistance is less than 1,0 × 10 6 Ω Then proceed to the next position or specimen
If the indicated resistance is equal or higher than 1,0 × 10 6 Ω, de-energize the instrumentation and repeat the procedure using (100 ± 5) V
Line-powered instruments may need a different test lead configuration to accurately measure grounded items, ensuring that the equipment grounding conductor is insulated from the signal ground Furthermore, the high-potential test lead might need to be connected to the ground side of the item being tested Always refer to the manufacturer's instructions for the correct test lead setup.
Point-to-point resistance measurements
Connect two electrode assemblies (probes 3) to the instrumentation, ensuring the specimen is positioned on the test support with the testing surface facing upward Place the probes on the specimen's surface at a minimum distance of 250 mm from their longitudinal axes and at least 50 mm from the specimen's edges, as illustrated in Figure 6.
Energize the instrumentation at (10,0 ± 0,5) V and record the reading after (15 ± 1) s if the indicated resistance is less than 1,0 × 10 6 Ω Then proceed to the next position or specimen
If the indicated resistance is equal or higher than 1,0 × 10 6 Ω, de-energize the instrumentation and repeat the procedure using (100 ± 5) V
Figure 6 – Principle of point-to-point measurements
Surface resistivity ρ s
Take the following formula according to Figure 7: ρ s = 2πãR s / log e (d 2 /d 1 ) d 2 = d 1 + 2g where ρ s is the surface resistivity (Ω);
The surface resistance, denoted as \$R_s\$ (Ω), is influenced by the dimensions of the contact electrodes The diameter of the center contact electrode is represented as \$d_1\$ (m), while the inner diameter of the outer ring contact electrode is indicated as \$d_2\$ (m) Additionally, the gap between the contact electrodes is referred to as \$g\$ (m).
Volume resistivity ρ v
Take the following formula according to Figure 7: ρ v = R v (d 1 ) 2 ãπ / 4h where ρ v is the volume resistivity (Ωm);
R v is the measured volume resistance (Ω); d 1 is the diameter of the centre contact electrode (m); h is the specimen thickness (m)
Figure 7 – Configuration for the conversion to surface or volume resistivity
10 Resistance measurements for non-planar materials and products with small structures
General considerations
This method is ideal for testing items with irregular surfaces, as traditional concentric ring and parallel bar electrode configurations are limited to planar items Many packaging products, such as shipping tubes, trays, tote boxes, and carrier tapes, do not have flat surfaces The probe utilizes springs to maintain consistent contact pressure between the electrode and the item, with acceptable variance due to wear, contamination, and manufacturing tolerances Additionally, elastomeric electrodes help accommodate uneven surfaces, ensuring consistent results across different laboratories and test operators.
Equipment
Probe
Refer to Table 1 and Figure 8
The two-point probe features an insulated metal body with polytetrafluoroethylene (PTFE) insulators at each end One insulator accommodates test leads, while the other contains receptacles for spring-loaded pins, one of which is encased in a cylindrical insulator and a metal shield The gold-plated pins exert a spring force of (4.6 ± 0.5) N over a travel distance of (4.3 ± 0.1) mm, with tips designed to fit friction-fitted electrically conductive rubber electrodes measuring (3.2 ± 0.1) mm in diameter These rubber electrodes, with a Shore A durometer hardness of 50 to 70 (per ISO 7619-1), are (3.2 ± 0.1) mm long and must demonstrate a point-to-point resistance of less than a specified value when tested on a stainless, non-corrosive metal plate (excluding aluminum).
Table 1 provides a list of the key components in Figure 8
Table 1 – Material for two-point probe
PTFE insulators Approximately 25,4 mm length and 12,7 mm diameter
Electrode shield Metal tubing approximately 31,8 mm length and
4,75 mm diameter Electrode insulator Heat shrinkable PTFE or other insulator
Receptacles Receptacle – with solder cup Interconnect Devices Inc., R-5-SC Pins Spring pin force is (4,6 ± 0,5) N at (4,3 ± 0,1) mm of travel; tip machined to accept electrode Interconnect Devices Inc., S-5-F-16.4-
Electrodes (3,2 ± 0,1) mm long, (3,2 ± 0,1) mm diameter conductive material, Shore A durometer hardness between 50 and 70 (ISO 7619-1)
This document provides key elements for probe construction, enabling performance replication, but it is not a complete materials list Refer to Figure 8 for part placement The listed parts are examples of commercially available products for user convenience and do not imply endorsement by IEC Equivalent products may be utilized if they yield the same results.
Figure 8 – Two-point probe configuration
Sample support surface
An insulating surface, when used for specimen support, shall have a surface resistance greater than 1 × 10 13 Ω, measured according to IEC 62631-3-2.
Resistance measurement apparatus
Resistance measurement apparatus as specified in 8.1 shall be used
NOTE The probe body size and shape are not critical to the measurement and may be of any convenient shape and size Photo
NOTE A constant output meter as specified in 8.1.2 was used to collect all data used to validate this standard test method Data was not collected to validate this equipment configuration.
Test leads
Test leads appropriate for the meter are required A shielded lead from the probe body to the instrument will greatly reduce electrical interference (see Figure 9)
NOTE Measurements for the validation of this test method were made using a shielded lead
Figure 9 – Probe to instrumentation connection
Shiel Voltage source Ammeter Ammeter Voltage source
Figure 10 – Spring compression for measurement
Test procedure
To conduct the test, first connect the probe to the meter as illustrated in Figure 9 Next, place the specimen on the sample support surface and compress the spring-loaded pins downward by approximately half their travel length (refer to Figure 10) Apply a voltage of (10.0 ± 0.5) V for (15 ± 1) seconds and observe the resistance If the resistance is less than 1.0 × 10^6 Ω, record the value and proceed to the next step If the resistance is greater than or equal to 1.0 × 10^6 Ω, increase the voltage to (100 ± 5) V and repeat the measurement, recording the resistance value Finally, repeat the test for each remaining specimen.
NOTE 1 A change in the size of the specimen can affect the measurements
Resistance measurements can be influenced by the dimensions and distance between electrodes For this study, electrodes with a diameter of 3.2 mm and a spacing of 3.2 mm were chosen to evaluate a diverse array of packaging types and sizes.
Resistance measurements of a specific sample material can fluctuate due to several factors, including variations in the surface composition or thickness of the sample, the compression exerted by the electrodes, inconsistencies in the resistance of the electrode material, alterations in material properties caused by the measurement current, and the cleanliness of both the electrodes and the sample.
NOTE 4 Testing of various electrode materials indicates that the use of harder rubber materials than specified creates greater variation in readings
The resistance of a specimen can fluctuate based on test conditions, leading to inherent non-uniformity in materials Consequently, measurements typically exhibit a reproducibility of only ±10%, with variations potentially reaching an order of magnitude under seemingly identical conditions To ensure comparability of measurements across similar specimens, it is essential to conduct tests with consistent voltage gradients.
Probe resting on test item
No spring compression Probe springs compressed about half of the travel distance for measurement
The repeatability of these test methods is estimated to be around half an order of magnitude For a series of laboratory tests with an average value of \$5 \times 10^{10} \, \Omega\$, the expected range of values is from \$2.5 \times 10^{10} \, \Omega\$ to \$7.5 \times 10^{10} \, \Omega\$.
The test report must encompass essential details such as the material's description and identification, including name, grade, color, manufacturer, and manufacturing date It should specify the shape, dimensions, and quantity of the specimens, along with the type, material, and dimensions of the probes if they differ from the standard Additionally, the report must outline the conditioning of the specimens, including temperature, relative humidity, and duration, as well as the cleaning procedures and test conditions at the time of measurement Instrumentation details, including type and calibration information, should be included, along with the test voltage and electrification time, noting any fixed or specified parameters The report should present the number of measurements, individual results, and average values for surface and volume resistivity, if applicable It must also identify resistance-to-ground and point-to-point resistance test positions, specifying the methods used and the distance between probe axes if different from the standard Finally, the report should document the dates of specimen preparation and testing, along with any specific observations made during the test, such as polarization effects.
When product standards or specific requirements are not provided, it is essential to consider how average values are determined Typically, the arithmetic mean is employed for this purpose, which involves summing up \( n \) values and dividing the total by \( n \).
1 where x is the average value; x i is an individual value; n is the number of values to be averaged
The geometric mean is often more relevant than the arithmetic mean for averaging values that differ significantly in magnitude, such as resistance measurements For instance, if four resistance measurements are around \$1 \times 10^9 \, \Omega\$ and one is \$1 \times 10^{12} \, \Omega\$, the arithmetic mean is skewed by the larger value In contrast, the geometric mean provides a more accurate representation of a material's performance by not being influenced by extreme values It is calculated by taking the nth root of the product of n values, ensuring a balanced average.
= where x is the average value; x i is an individual value; n is the number of values to be averaged
The test report shall state if arithmetic or geometric mean has been used to calculate average values
System verification for surface resistance measurements
Fixture and procedure for lower resistance range
The fixture must adhere to the electrode dimensions specified in section 8.2.2, featuring 20 individual metal surfaces that contact the inner electrode and 20 identical pads for the outer electrode All pads should be flat and mounted on a level surface The fixture will include 20 resistors, each measuring (1.00 ± 0.01) × 10^6 Ω, installed on the bottom side, with each resistor connected between an inner and outer pad (refer to Figure A.1) Additionally, the fixture material must exhibit a volume resistance of at least 10^8 Ω between the two rows of pads when unconnected by resistors, tested at (100 ± 5) V.
Figure A.1 – Lower resistance range verification fixture for surface resistance measurements
Prior to a test, the system shall be checked for proper operation as follows:
The assembly outlined in section 8.2.2 is connected to the instrumentation as shown in Figure 3 and positioned on the fixture A voltage of (10.0 ± 0.5) V is applied, and a reading is recorded after (15 ± 1) seconds The expected result is (5.00 ± 0.25) × 10^5 Ω This check is subsequently repeated after rotating the assembly by 90 degrees.
NOTE Rotation of the electrode assembly checks the flatness of the fixture and electrode containing surfaces
Fixture and procedure for upper resistance range and determination of
The fixture must adhere to the electrode dimensions specified in section 8.2.2 and feature metal surfaces or pads that contact the electrode surfaces These pads should be flat, free of protrusions, and securely mounted on a flat surface They can be interconnected using wire or complete circular rings A single resistor of (1.00 ± 0.05) × 10^{12} Ω is required to connect the center (inner) and ring (outer) contact surfaces, as illustrated in Figure A.2 Additionally, the resistor and wiring must be installed on the underside of the fixture.
(500 ± 25) V in compliance with IEC 60167, the material for the fixture shall have an insulation resistance of at least 10 14 Ω between the two rows of pads when not connected by a resistor
Figure A.2 – Upper resistance range verification fixture for surface resistance measurements
The following procedure confirms the capability of the system to measure 1,0 × 10 12 Ω and offers a method to determine the electrification period as follows:
The assembly outlined in section 8.2.2 is connected to the instrumentation as shown in Figure 3 and positioned on the fixture A voltage of (100 ± 5) V is applied, and a reading is taken once the displayed value stabilizes If the reading falls within the resistor's tolerance range, the procedure is repeated five times, recording the time taken for the instrument to reach a steady-state value The average of these five recordings determines the electrification time Adding 5 seconds to this time establishes the electrification period, which is used for measuring specimens with resistances greater than \(10^6 \, \Omega\).
System verification for volume resistance measurements
Fixture and procedure for lower resistance range
Prior to the test, the system shall be checked for proper operation as follows:
Connect probes 1 and 2 to the instrumentation as shown in Figure 4, ensuring no specimen is placed between them Insert a resistor of (5.00 ± 0.05) × 10^5 Ω between the voltage source output and probe 2 Apply a voltage of (10.0 ± 0.5) V and take a reading after (15 ± 1) seconds, expecting a result of (5.00 ± 0.25) × 10^5 Ω.
Fixture and procedure for upper resistance range and determination of
The following procedure confirms the capability of the system to measure 1,0 × 10 12 Ω and offers a method to determine the electrification period as follows:
Connect probes 1 and 2 to the instrumentation as shown in Figure 4, ensuring no specimen is placed between them Insert a resistor of (1.00 ± 0.05) × 10^{12} Ω between the voltage source output and probe 2, and apply a voltage of (100 ± 5) V Take a reading once the displayed value stabilizes If the reading falls within the resistor's tolerance range, repeat the process five times, recording the time taken for the instrument to reach a steady-state value The average of these five recordings will determine the electrification time To measure specimens with resistance greater than 10^{6} Ω, add 5 seconds to the electrification time to establish the electrification period.
System verification for resistance measurements for non-planar materials
Verification fixtures
The low resistance verification fixture features a resistor of value (1.00 ± 0.01) × 10^5 Ω, securely attached to two metal contact plates These plates are designed to ensure that each probe electrode makes contact with only one plate, preventing any contact between the plates themselves Additionally, the plates can be mounted on a material that shares similar properties with the sample support surface A visual representation of a potential configuration for this resistance verification fixture is provided in Figure A.3.
The high resistance verification fixture features a resistor of value (1.00 ± 0.05) × 10^9 Ω, securely attached to two metal contact plates Each plate is designed to ensure that probe electrodes make contact with only one plate, preventing any contact between the plates themselves The dimensions of the plates must be a minimum of 3.3 mm in length and width for rectangular shapes, or at least 3.3 mm in diameter for circular shapes, with a maximum gap of 3.1 mm between them Additionally, the plates can be mounted on a material that shares similar properties with the sample support surface.
The actual value of the resistors shall be measured periodically This measured value shall be used to verify probe operation
Verification procedure
The verification procedure involves several key steps: First, ensure correct probe operation by measuring known resistance values Connect the probe to the meter as illustrated in Figure 9, and place the probe electrodes onto the low resistance verification fixture shown in Figure A.3 Next, compress the spring-loaded pins downward by approximately half their travel length (refer to Figure 10) Apply a voltage of (10.0 ± 0.5) V for (15 ± 1) seconds and observe the resistance, which should be recorded and must fall within 10% of the actual resistor value Finally, repeat the procedure using the high resistance verification fixture at (100 ± 5) V.