Powering an electromechanical relay with an NI-9481 module.

[nick525]

 I am trying to use an NI-9481 on an NI cDAQ-9172 to generate a digital output voltage to power an electromechanical relay. I can manage to switch the different channels of the NI-9481 on and off; however, the electromechanical relay I am attempting to power refuses to turn on. Is it truly possible to generate a voltage using the digital output on the NI-9481? If so, what logic would I use for labVIEW 8.0 to create this voltage? Thanks in advance for any help with my problem.

Nick

[Ben]

It sounds like you are only asking part of the question.

To pick a relay requires work so the question is "Does the output provide enough power?"

Power (in DC) is current X Voltage.

Add to that

current = voltage / resistance

and you should be able to check the spec on your relay and the DO lines and answer this Q.

Ben

[10Degree]

Nick,

It looks like the 9481 is a SPST relay device - it will not generate a voltage to turn on your external relay.  You can use the 9481 to switch on power for an external device.  Look at page 8 & 9 of the 9481 spec (http://www.ni.com/pdf/manuals/373507c.pdf).

-cb

[nick525]

Thanks for the help. I found an external power supply and solved my problem. Now I have a few more questions.

First, can I output a voltage with the NI-9205 module running on the same cDAQ? If so, how?

Second, what labVIEW logic would I use to fire three of the four channels in my NI-9481 relay in a given sequence as input by the user? (Example: Channel 1 cycles on for 8 minutes, switches off for a day and a half, then channel 2 cycles on for eight minutes, then switches off, then channel 3 cycles on immediately for 2 minutes, then switches off.)

[LabViewGuruWannabe]

To program your relay sequence, use a State Machine with any of the several Timer functions. Personally, I like to use the Event Structure with the state machine inside the Timeout event.

I'll see if I can whip up a quick example.

B-)

[LabViewGuruWannabe]

This should give you a general idea of using a state diagram and event structure to control your sequence. I don't have the code to communicate with your NI-9481 module, but you can get the general idea.

I based it on the following default sequence: (I used seconds for testing instead of minutes or days, of course)

Initialize - All Relays OFF
(User Presses Start)
Cycle 1 - Relay 1 ON - 8 Seconds
Cycle 2 - All Relays OFF - 30 Seconds
Cycle 3 - Relay 2 ON - 8 seconds
Cycle 4 - Relay 3 ON - 2 seconds
Stop- All Relays OFF - Until Start

Hope this helps!

B-)

[nick525]

Thanks for the fast response. Is there any way to convert this example vi to use in labVIEW 8.0?

[LabViewGuruWannabe]

Sorry about that. The previous version was in 8.2. These should be 8.0.

B-)

[ryan_d]

Hi everyone,

LabViewGuruWannabe, it’s great to see such clean and organized code!

nick525, you will not be able to generate a voltage from the 9205 in cDAQ. The DO0 line is only available for use with cRIO. The KnowledgeBase Article: Using the Digital Output and PFI Lines of the 9205/6 with Compact DAQ explains the difference of functionality of the 9205 in cDAQ versus cRIO.

Please post back if you have any questions. Have a great day!

[nick525]

Thanks for all of the help guys, I really appreciate it, especially with the state machine. It's such a useful tool in labVIEW and I really had no idea how to use one. Thanks again!