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What Functions Do I Use to Operate My Compact DAQ Relay Module?

Primary Software: Driver Software>>NI-DAQmx
Primary Software Version: 8.3
Primary Software Fixed Version: N/A
Secondary Software: N/A
Hardware: CompactRIO>>Digital Output Modules>>NI 9481, CompactRIO>>Digital Output Modules>>NI 9485

Problem:
I have a cDAQ relay module and want to know what functions I can use with it. I have DAQmx Switches functions. Can I use them with my module?

Solution:
You cannot use DAQmx Switches functions to operate your cDAQ relay module. Instead, use the DAQmx Write (Digital 1D Bool NChan 1Samp 1Line) function.

For example, if you want to configure all 4 lines on a NI-9481 relay, perform the following steps:

1. First create a task in Measurment and Automation Explorer (MAX) and add all 4 channels on the cDAQ module to the task. 
2. Navigate to LabVIEW and place a DAQmx Task Name Constant on the block diagram. 
3. Select the task that you have made, then right-click the DAQmx Task Name and select Generate Code» Configuration. This will automatically generate a VI which contains the code needed to configure the channels related to the task. 
4. Wire the new VI to a DAQmx Write (Digital 1D Bool NChan 1Samp 1Line) function. 
5. Wire a constants to the auto start input terminal and data input terminal on this VI by right-clicking the terminals and selecting Create»Constant.  Verify that the auto start constant is set to true. The data input constant will be an array of Booleans. The number of Booleans in the array should be set to match the number of channels in the task. 

After these steps, the VI created should look like the VI pictured in Figure 1.

Figure 1: Configure 4 Channels on the NI-9481

There are 4 channels configured in the task and therefore there are 4 elements in the data array. The first Boolean constant applies to the first channel configured in the task; the second Boolean constant applies to the second channel configured in the task and so on. If the Boolean constant value is true, the switch on the corresponding relay will close. If the Boolean constant value is false, the switch on the corresponding relay will open. This is illustrated in Figure 2.

Figure 2: Impact of a DAQmx Write on the NI-9481

Related Links: KnowledgeBase 4D3F2P9S: How Do I Check the Status of the Relays on My NI 948x Compact DAQ Relay Module?

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Report Date: 12/22/2006
Last Updated: 09/04/2007
Document ID: 44LAPTNP

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