DC and AC Current
The NI 4070/4072 allow you to measure currents ranging from a few nanoamperes to an ampere.
DC Current mode and AC Current mode have three ranges each for the NI 4070/4072: 20 mA, 200 mA, and 1 A for DC current; 10 mA, 100 mA, and 1 A for ACrms current. The AC Current mode uses the same fast measurement technique as the AC Volts DC Coupled mode.
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Note AC current measurements are always DC coupled and therefore always offer low settling time. Keep in mind that the range chosen needs to include both the signal range and its offset, otherwise the input can get overloaded. For a list of the available ranges, refer to Related Documentation for the NI 4070/4072 specifications document. |
Shunt Resistor
For all ranges, the current you measure flows through a stable onboard 0.5 Ω precision shunt resistor with temperature coefficient and power ratings selected to reduce resistor self-heating errors. For the effect of temperature changes on the accuracy of the measurements, refer to Related Documentation for the NI 4070/4072 specifications document and the temperature coefficient.
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Tip The current measurement path within the NI 4070/4072 utilizes an electromechanical relay that provides very low resistance to assure a low burden voltage. While this relay has an exceptionally long life, you can take special precautions to ensure reliable operation.
Whenever possible, switch the NI 4070/4072 into the current measurement function before applying the current. Switching inductive current sources generally creates flyback voltages that stress the relay and, if done frequently, can shorten the reliability of the relay. Also, avoid interrupting the current by switching out of the current measurement function when currents are flowing through the circuit. |