What are you looking for?
Tip 5: Output Voltage Clamping
Resistance measurements on certain types of contacts may require a limitation on the voltage applied to the material during a resistance measurement. Both the voltage used to make the measurement and the open circuit voltage should be considered. The need for voltage limitation arises from the possibility that oxidation on the contact surfaces may increase the resistance reading. If the voltage is too high, the oxide layer may be punctured resulting in a lower resistance reading. Not all DMMs offer built-in voltage clamping circuits.
An example of a multimeter that offers a voltage clamping circuit is the 34420A. The 34420A provides a programmable level of open circuit clamping. The voltage-limited measurement is available on the 10 and 100 ohm ranges. The open circuit voltage and measurement voltage can be clamped at one of three levels, 20 mV, 100 mV, or 500 mV.
| Range | Test Current | Measurement Voltage (Full Scale) | Open Circuit Voltage (Full Scale) |
|---|---|---|---|
| 10Ω | 1 mA | 10 mV | 20, 100, or 500 mV |
| 100Ω | 0.1 mA | 10 mV | 20, 100, or 500 mV |