|
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.
|
