Avoiding Measurement Problems

Condition Effect Suggestions
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. 
Ambient temperature 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 Humidity may cause leakage effects on high resistance components.
  • Maintain relative humidity  under 50%.
Thermal emf 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.
Low resistance Lead resistance and thermal emf may introduce errors.
  • Use 4-wire measurement, Kelvin leads.
  • See thermal emf (above).
High resistance 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 loops Ground currents can introduce noise and offset voltage.
  • Use radial grounds to only one reference point.
Test conditions 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.