|Power applied to Device Under Test (DUT)
||Self heating in resistive components causes a temperature effect and a corresponding resistance change.
- Use low test signals or pulsed measurement.
- Heat sink the DUT.
- Allow for effects of power coefficient of resistance.
- Use low power coefficient components.
|High voltage applied to DUT
||Some high resistance resistors have a significant voltage coefficient of resistance.
- Use low voltage coefficient components.
- Measure at low voltages.
- Allow for the effects of the voltage coefficient of resistance.
||Temperature coefficient effects; possible permanent retrace effects may result from large shipping or storage temperature shifts.
- Maintain stable temperature and minimize exposure to temperature extremes.
||Humidity may cause leakage effects on high resistance components.
- Maintain relative humidity under 50%.
||The thermal emf, i.e. the voltage generated at contacts of dissimilar metals at temperature gradients, can cause erroneous voltage and resistance measurements.
- Use Cu. to Cu. contacts and leads wherever possible; silver contacts and solder are acceptable.
- Avoid using steel and brass.
- Minimize temperature gradients or drafts.
- Use switched or "true ohm" measurement instruments.
- Alternate leads to determine the degree of the problem.
||Lead resistance and thermal emf may introduce errors.
- Use 4-wire measurement, Kelvin leads.
- See thermal emf (above).
||Leakage through lead insulation and bench top, resulting from humidity, may cause errors.
- Use low leakage insulation such as Teflon
- Set DUT on high insulation sub-plate.
- Maintain all terminals clean.
- Shield and avoid high voltage and movement nearby.
- Use 5 or 6 terminal guard circuit.
||Ground currents can introduce noise and offset voltage.
- Use radial grounds to only one reference point.
||Most resistors, capacitors, and inductors are non-ideal; wire wound resistors are both inductive and capacitive; capacitors have losses, and inductors can be very resistive. Test conditions of voltage, frequency and model (parallel or series) may be significant to the measurement.
- Apply the instrument test conditions that are the most representative model of the DUT.