How Much Power? Worst-Case, Measured, and Typical Power Consumption
The CompactRIO power requirement specifications in hardware documentation assume the worst possible part conditions, the highest allowable temperature range, and the most demanding applications. The most common way to calculate the power requirement of a CompactRIO system is to take the published, worst-case power requirements of all parts of the system and add them together. Although summing the individual power requirements may provide useful information, the actual power requirement of your system is always less than the sum of individual published power requirements.
The most reliable way to determine the power requirement of your CompactRIO application is to measure the power consumption while the system is running. This document explains how to measure CompactRIO power consumption.
Measuring the Power Consumption of a CompactRIO System
For a DC circuit, the power consumption in watts (W) is the product of the applied voltage and the current. This section explains how to measure the voltage across the positive and negative voltage terminals of the power supply input and the current through the entire circuit.
- CompactDAQ chassis (recommend cDAQ-9185)
- C Series Voltage Input Module (recommend NI-9221)
- C Series Current Input Module (recommend NI-9227)
- Power Supply (recommend NI PS-15)
Connecting the Hardware
To measure the current through the circuit, connect the NI-9227 in series with the power supply and the voltage input terminal of the CompactRIO controller. Complete the following steps.
- Connect the negative voltage terminal of the power supply to the C terminal of the CompactRIO power connector.
- Connect the positive voltage terminal of the power supply to the AI0+ terminal of the NI-9227.
- Connect the AI0- input of the NI-9227 to the V terminal of the CompactRIO power connector.
To measure the voltage, connect the NI-9221 in parallel with the CompactRIO power connector. Complete the following steps to connect the NI-9221 across the positive and negative voltage terminals of the power connector.
- Connect the V terminal of the CompactRIO power connector to the AI0 terminal of the NI-9221.
- Connect the C terminal of the CompactRIO power connector to the COM terminal of the NI-9221.
Measure the voltage and current at the same time to find the instantaneous power consumption. For best results, wait until your application is running normally and the power consumption has settled to a stable level, then calculate average power consumption from a set of measurements.