Archived: M-series: External AO Reference

Publish Date: Jan 10, 2019 | 1 Ratings | 4.00 out of 5 | Print | Submit your review


This document has been archived and is no longer updated by National Instruments.

The M-series devices have the option of explicitly specifying a reference value for the output voltage of an analog output. This will set the output range so that you can maximize the resolution of your output. The smaller the range of your output, the better resolution you will have. There are 2^number of bits of resolution steps over the entire range of a DAQ board. By decreasing the range, you will also decrease the voltage difference between each step. Therefore, there is an inverse relationship between the range of your output and its resolution. Halving your range will give you twice as good resolution.

This example program demonstrates how to use an external reference to control the resolution of the output. The output is a continous waveform on an analog channel. The external reference input pin is shared with the analog trigger input pins, and is therefore, labeled as apfi0 on the first connector and afpi1 on the second. In this program, either the apfi0 or apfi1 line can be used. The program uses a DAQmx property node to specify that an external reference will be used and which line the input will be on. It is important to note that you must also specify the value that you plan on using externally by inputting it to the property node. Make sure to specify the same value as you are supplying externally or your output values will be scaled proportional to the ratio of the actual external voltage and the one specified programmatically to the property node.

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