# Measuring Current

NI Digital Multimeters Help (NI-DMM 18.1)

Edition Date: March 2018

Part Number: 370384V-01

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This section describes how to measure current on National Instruments DMMs.

## Measuring Current Within the Normal Range (NI 4050 is not supported)

To configure current measurements within the normal range on the DMM, use one of the following two methods:

### Method 1

1. Select the current measurement function.
2. Take a reading from the DMM immediately.

### Method 2

1. Configure the DMM for a software trigger.
2. Initiate the DMM for a current measurement to cause the input relay to switch.
3. Send a software trigger to the DMM to take a measurement.

## Using Current Shunt Modules

When taking current measurements outside of the specified range on the DMM, and when taking any current measurements on the NI 4050, you must use a current shunt module. NI offers the NI CSM-10A and the NI CSM-200mA current shunt modules. The NI CSM-10A has a 0.01 Ω sense resistor, and the NI CSM-200mA has a 1.0 Ω sense resistor.

 Note  For valid current ranges, refer to the specifications document for your device.

Each current shunt module (CSM) operates by passing the input current through a precise resistor. The following figure shows the internal circuitry of the CSM:

 1 Voltage Across Resistor (VOUT) 3 Fuse 2 Precision Resistor 4 Current Source (IIN)

To configure current measurements using the NI CSM-200mA or the NI CSM-10A, perform one of the following two methods:

### Method 1

1. Measure the voltage drop across the resistor of the CSM.
2. Use this value to calculate the current using Ohm's Law, as follows:

IIN = (VOUT)/R

where

I is the input current

V is the voltage across the precision resistor

R is the resistance of the precision resistor

For example, assume that you are using the CSM-200mA, which has a 1 Ω precision resistor, and the measured voltage is 50 mV. Apply these values to Ohm's Law to determine the current, as follows:

50 mA = 50 mV / 1 Ω

 Note  You can use the NI CSM-10A current shunt with any NI DMM for this method. You can also use the NI CSM-200mA current shunt with the NI 4050.

### Method 2 (NI 4050 only)

For LabVIEW:

1. Call niDMM Config Measurement.
2. Specify the shunt value in the Shunt Value property node.
3. Call niDMM Read to obtain the value of the measurement.

For C/C++/CVI/Visual Basic:

1. Call niDMM_ConfigureMeasurementDigits.
2. Specify the shunt value in the NIDMM_ATTR_SHUNT_VALUE attribute.