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NI 9477 Data input

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Hello all,


I am working on a LabVIEW program to switch on and off a relay and I am confused as to what the data input is supposed to be for the DAQ Assist for the NI 9477 module.  If I set the 'data' input to a constant, an integer control as well as a T/F control becomes wired to the 'data' input.  What is the format of data that I am supposed to input.  On first glance, I thought the integer control was the voltage I would like to output and have no idea what the T/F control is for...




Message 1 of 7

Hi Justin,


To control the on and off we normally use the Boolean array as a representation of all lines in the port (for the data terminal). The integer control is to send information such as numbers trough the lines. Like in the example attach. For your application the Boolean control would be more appropriate. The digital outputs are TTL signals so there is no control over the voltage levels.

Alejandro C. | National Instruments
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Message 2 of 7

Thanks for your help!  So, I understand that for TTL signals, there is a logic low (0-0.8V) voltage signal and a logic high (2-5V) voltage signal that is outputted.  The module outputs 5-60V which is out of both logic ranges which definitely tells me that I am not understanding something correctly.  I need to know roughly the voltages that are outputted so that way I can get a relay with the correct switching voltage.  So what I am not understanding correctly about this module?


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Message 3 of 7
Accepted by booxcar

A high/low signal open/close the lines for voltage sinking, take a look at the figure 2 in page 8 from the NI 9477 Operating Instructions and Specifications. It's simply closes the electrical path, just like a switch. The module can handle external power supply voltage range from 0–60 VDC it is not sourcing by itself the voltage. I hope this helps

Alejandro C. | National Instruments
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Message 4 of 7

Ah, I see how this all works now.  Thanks for your help!

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Message 5 of 7

So, what minimum control voltage should I look for when it comes to the relay?  If the high logic is 2-5V, will a 3-24VDC control voltage range be acceptable to switch on and off the relay?

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Message 6 of 7

The software is triggering the TTL signal that open/close the internal switch. This voltage is isolate from the line itself so the external power supply will not mix with the control line.

Alejandro C. | National Instruments
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Message 7 of 7