USB-6008 Voltage Response Output

[Bren327]

Hi guys,

I created a LabVIEW program to continuously monitor the temperature of a bioreactor, using an NI USB-6008 multifunction I/O. I'm using LabVIEW 2017 and DAQmx 17.1. I have the program working, measuring the voltage through the thermistor, converting to temperature, and continuously displaying and recording. I also have a feature that turns on an alarm any time the temperature exceeds a chosen threshold.

The end goal is a response system where the temperature is monitored continuously, and I would like the system to automatically turn on an air pump any time the threshold temperature is exceeded. I need to be able to trigger an analog output voltage of at least 3.5V from the USB-6008 to a solid state relay to run the pump. Does anyone know how I can build this trigger correctly?

[crossrulz · Accepted solution]

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Bren327 wrote:

I need to be able to trigger an analog output voltage of at least 3.5V from the USB-6008 to a solid state relay to run the pump. Does anyone know how I can build this trigger correctly?

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Use one of the Digital IO lines.  Then you just write the result of the comparison directly to the digital output.  The digital lines will put out a TTL (5V logic) signal, but not a lot of current.  So if your SSR needs more than 5mA for the control line, I would recommend adding some circuitry to allow for more current (do a search at Digikey in the Logic - Buffers, Drivers, Receivers, Transceivers section).

But if this is a serious application where safety is a concern, I would use a cRIO or one of the Ethernet Expansion Chassis.  Then the FPGA can handle the acquisition and control and just pass the data up to the host.  I do this because Windows likes to crash, but the FPGA can keep running at its deterministic rate and therefore perform the safety critical functions.

[Bren327]

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@crossrulz wrote:

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Use one of the Digital IO lines.  Then you just write the result of the comparison directly to the digital output.  The digital lines will put out a TTL (5V logic) signal, but not a lot of current.  So if your SSR needs more than 5mA for the control line, I would recommend adding some circuitry to allow for more current (do a search at Digikey in the Logic - Buffers, Drivers, Receivers, Transceivers section).

But if this is a serious application where safety is a concern, I would use a cRIO or one of the Ethernet Expansion Chassis.  Then the FPGA can handle the acquisition and control and just pass the data up to the host.  I do this because Windows likes to crash, but the FPGA can keep running at its deterministic rate and therefore perform the safety critical functions.

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Thanks! The digital line worked perfectly. As for the second part, there are no safety hazards involved in our reactor; it's more of a glorified composter, but I may look into that since we have previously lost data with a computer crashing or shutting down. Thanks for the help!