Home Instrumentation How to Make Low Current Draw Measurements with a Digital Multimeter

How to Make Low Current Draw Measurements with a Digital Multimeter

How to Make Low Current Draw Measurements with a Digital Multimeter

A multimeter is an indispensable tool for most engineers and technicians when making current or voltage measurements. Nevertheless; When there is a need to measure the power consumption of a device, most multimeters often do not meet the necessary requirements: work at a high sampling rate, sufficient current measurement ranges, or a quick dump of the data. data to PC for further analysis. The Keysight Technologies 34465A/34470A multimeters provide, in addition to current, voltage, frequency, period, temperature... measurements, current measurement ranges and sampling rate ideal for consumption measurement.

Most common consumption metering applications

Characterization of the power consumption of a battery-powered device

Design engineers continually work on optimizing the current consumption of their devices, but to do so they need accurate and reliable current measurements from idle to full power to fully characterize current cycles. The typical working ranges for these applications go from mA to 10A, so a measurement resolution of at least: microamps is necessary.

Test of the current consumption of a low leakage diode, or characterization of materials

To test the current draw of a low-leakage diode, a pico-amp resolution with an upper limit of tens of mA is necessary. Although these measurements (and power) can be made with a higher performance electrometer, the most versatile and economical solution involves the use of a stable DC power supply and one of Keysight's new Truevolt multimeters. These devices have a low current range for measurements of up to 1μA with a resolution of pA and a deviation of less than 100pA. Its upper current limit amounts to 10A in both direct and alternating current.

Dynamic current measurements

Dynamic current measurements can be quite complex because a range change of the DMM is necessary based on the level of current being measured. Keysight has specialized instruments (such as the SMU N6782A) that can simultaneously digitize power, voltage, and current without range issues. While this can be a great solution for certain current characterization applications, the option of using a Truevolt meter is much cheaper. A visual example: this figure depicts the discharge of a battery, with a dynamic range of measurement automatically adjusted with the autoranging function.

4 tips for making these measurements

1. When measuring very small currents, be sure to clear previous readings from the display to speed up the meter's autoranging and override possible offset settings, and memory for use throughout the measurement cycle (one alternative is the simultaneous download of data to the PC).

2. Consider positioning the multimeter in series with the power supply from the positive side. This way, if you increase the voltage enough to exceed the load voltage of the DMM (generated by the flow of charge through the internal resistance of the multimeter), you can supply the correct voltage to your device and measure the current with the highest multimeter accuracy.

3. By using the digitizing capability of Keysight multimeters and the High Speed ​​option, you can measure highly changing parameters with time with a time resolution of 20 μs. To scan effectively with exact timing you must ensure that auto zero and auto ranging are disabled. This eliminates the delays that are introduced when the DMM makes additional readings for auto zero or shift to a different range.

4. Use Keysight's BenchVue software to remote control and launch measurements from two DMMs simultaneously. Also, use the digitizing mode of the DMM to ensure a synchronization of 20 μS/sample between each device. Finally, note that the data logging mode via BenchVue on a PC includes by default the input of header data which may slightly interfere with the measurement when extremely accurate timing is required.

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1. When measuring very small currents, be sure to clear previous readings from the display to speed up the meter's autoranging and override possible offset settings, and memory for use throughout the measurement cycle (one alternative is the simultaneous download of data to the PC).

2. Consider positioning the multimeter in series with the power supply from the positive side. This way, if you increase the voltage enough to exceed the load voltage of the DMM (generated by the flow of charge through the internal resistance of the multimeter), you can supply the correct voltage to your device and measure the current with the highest multimeter accuracy.

3. By using the digitizing capability of Keysight multimeters and the High Speed ​​option, you can measure highly changing parameters with time with a time resolution of 20 μs. To scan effectively with exact timing you must ensure that auto zero and auto ranging are disabled. This eliminates the delays that are introduced when the DMM makes additional readings for auto zero or shift to a different range.

 4. Use Keysight's BenchVue software to remote control and launch measurements from two DMMs simultaneously. Also, use the digitizing mode of the DMM to ensure a synchronization of 20 μS/sample between each device. Finally, note that the data logging mode via BenchVue on a PC includes by default the input of header data which may slightly interfere with the measurement when extremely accurate timing is required.


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