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The most common causes for different surface and volume resistance measurements
Measurement deviations in resistance measurement are among the most common challenges in determining the Surface or volume resistance of plastics, coatings and other materials.
Our own laboratory measures a surface resistance of 10⁶ Ω, while the customer 10⁸ Ω Determined. Both measurements were carried out with high-quality measuring instruments – and yet the results differ by two orders of magnitude.
The question quickly arises:
Who measured correctly?
The answer is often: Both.
Because the resistivity This is one of the measurement methods that are particularly sensitive to measurement conditions. Even small differences in Measurement setup can have a significant impact on the outcome.
In this article, we show the most common causes for differing measurement results and explain how reproducible measurements can be achieved.
Why measurement deviations occur in resistance measurement
The electrical resistance A material does not have a fixed material constant, such as density.
Especially with plastics, coatings, composites, or ESD materials, the measurement result depends on numerous influencing factors. Therefore, standards such as... IEC 61340 2 3, ASTM D257 or DIN EN 1081. (for the electrical resistance of floor coverings) precise measurement conditions.
If these conditions are not met or if they differ between two laboratories, different measurement results will inevitably occur. Measurement deviations in resistance measurement These occur when the measurement setup or environmental conditions differ.
Checklist: These 8 factors should be checked if measurement results differ.
If surface or volume resistance measurements differ, the cause is often not the measuring instrument itself. In most cases, individual test conditions or the measurement setup differ.
The following checklist will help you identify the most common causes of Measurement deviations in resistance measurement systematically narrow it down.
1. Are the temperature and humidity correct?
temperature and humidity These are among the most common causes of inaccurate measurement results. Many conductive or dissipative materials – especially plastics – are sensitive to moisture. Even slight changes in environmental conditions can measurably affect surface or volume resistance.
Possible effects:
Even slight changes in environmental conditions can lead to fluctuating measurement results and make it difficult to compare data between different laboratories.
Practical tip: Condition the test specimens under identical climatic conditions before measurement and document the temperature and humidity.
2. Was the same measuring voltage used?
Not all materials behave the same electrically. While metallic conductors exhibit almost the same resistance regardless of the applied voltage, the resistance of many plastics and insulating materials can vary significantly with the voltage. Measuring voltage change.
For example, are different Test voltages When used, the measurement results are often not directly comparable.
Possible effects:
Different Measuring voltages This can lead to identical materials exhibiting different resistance values.
Practical tip: Document the measurement voltage used along with the measurement result and only compare measurements taken under identical conditions.
3. Was the same electrode used?
The used Electrode has a direct influence on the measurement result. Depending on the application, for example... Ring electrodes, concentric electrodes, four-point probes or spring contacts for use. Different Electrode geometries They generate different electrical measuring fields and can therefore lead to differing resistance values.
Possible effects:
Different electrode geometries influence the measurement field and can therefore cause differing measurement results.
Practical tip: For comparative measurements, use the same one if possible. Electrode and the same Measurement setup.
4. Was the contact pressure identical?
Especially at soft plastics, elastomers or powder samples The contact pressure affects the size of the contact area between the electrode and the test object. This can also change the measured resistance.
Possible effects:
Even slight differences in contact pressure can change the contact resistance and impair the reproducibility of the measurement.
Practical tip: Use measuring systems with whenever possible defined contact pressure and avoid varying manual loads.
5. Was the measurement taken for a sufficient length of time?
Especially high-resistance materials It takes time for a stable measured value has been set. If the measurement is stopped too early, lower or fluctuating values may occur.
Possible effects:
If the measurement is stopped too early, unstable or excessively low readings may be recorded.
Practical tip: Wait until the Measured value stabilized has before you document it.
6. Is the surface clean?
Fingerprints, dust, release agents or production residues can Surface resistance significantly affecting the results. Even the smallest impurities are enough to distort measurement results.
Possible effects:
Contamination or residues on the material surface can significantly distort the measured surface resistance.
Practical tip: Check the Measuring surface before each measurement and clean the Material sample if necessary.
7. Was the measurement taken at the same location?
Conductive plastics or Coatings They do not always possess identical electrical properties across their entire surface. Differences in distribution conductive additives This can lead to different resistance values locally.
Possible effects:
Material inhomogeneities can lead to problems at various points. Measuring positions Different resistance values can be determined.
Practical tip: Take several measurements at different positions and evaluate the average.
8. Is the measuring device set correctly?
Even modern Resistance measuring devices They only deliver reliable results if they are regularly checked and used in the appropriate manner. Measuring range working. An unsuitable choice of measuring range can cause problems. Accuracy affect.
Possible effects:
An unsuitable measuring range or an unchecked measuring device can impair the accuracy and validity of the results.
Practical tip: Regularly check the condition of your Measuring device and choose that Measuring range matching the expected resistance.
The most important influencing factors at a glance
For reproducible resistance measurements, all relevant test conditions should be as identical as possible. Even small differences can influence the measurement result and make comparability difficult.
| factor | Suggestions |
|---|---|
| temperature and humidity | Ensure identical environmental conditions |
| Measuring voltage | Always use the same test voltage |
| Electrode | Use identical electrode geometry |
| contact pressure | Ensure constant contact pressure |
| measuring time | Measure until a stable reading is obtained. |
| Surface | Use a clean and dry measuring surface |
| Measuring position | Consider multiple measurement points |
| Measuring device | Select the appropriate measuring range and check it regularly. |
Here's what you should take away from this article
The key to reproducible measurement results
Different resistance measurements do not necessarily mean that a measurement was performed incorrectly. In many cases, differing test conditions are the cause of the differing measurement results.
Anyone wanting to achieve reproducible and comparable resistance measurements should therefore not only pay attention to a suitable measuring device, but also consider the entire measurement process. Identical environmental conditions, the correct measuring voltage, suitable electrodes, a defined measurement setup, and careful preparation of the material sample all contribute significantly to the quality of the measurement results.
With appropriate measuring technology and a consistently applied measurement methodology, measurement deviations can be significantly reduced and results can be reliably compared. Those who take the described influencing factors into account can Measurement deviations in resistance measurement significantly reduce the number of measurements and achieve reproducible results.
Do you want to check measurement deviations in resistance measurements or do you currently lack the appropriate measuring equipment? Then take advantage of NH Instruments' measurement service. We determine the surface and volume resistivity of your materials under defined measurement conditions and support you in evaluating the results.
Frequently asked questions about resistance measurement
Different test conditions, such as temperature, humidity, measuring voltage, electrode geometry, or contact pressure, can influence the measurement result. Therefore, resistance values should only be compared if they were determined under identical conditions.
Deviating measurement results do not necessarily mean that a measurement was performed incorrectly. Even small differences in the measurement setup or environmental conditions can lead to different resistance values.
The most important influencing factors include temperature, humidity, measuring voltage, electrode geometry, contact pressure, measuring duration, the condition of the material surface and the material composition.
Reproducible measurement results require identical test conditions. These include a defined measurement setup, suitable electrodes, constant environmental conditions, and a regularly checked measuring instrument.
Yes. If you would like to have the surface or volume resistivity of your materials determined, or if you would like to verify measurement results, we offer NH Instruments professional service measurements We will support you both in carrying out the measurement and in evaluating the results.
Learn more about our service measurements
Which measuring device is suitable depends, among other things, on... Resistance range, the Material and Measurement task Different resistivity measuring devices and electrodes are used for measuring surface and volume resistances, depending on the application.
Learn more about our resistivity meters
Measurement deviations in resistance measurement can be avoided by keeping all relevant test conditions – such as temperature, measuring voltage, electrode geometry and measuring duration – constant.
NH Instruments We specialize in measurement solutions for determining the electrical properties of materials. Our portfolio includes resistivity meters, electrodes, service measurements, and technical consulting for development, quality assurance, and research.
The questions are based on typical questions from our daily practice and from conversations with our customers. Should you have any further questions about resistance measurement or our measurement solutions, we look forward to hearing from you. Contacting us.
