Phidgets Forums

I assume it should be possible to use multiple DAQ1400 input devices with a VINT hub, but I have run into a problem.

I have two pressure transmitters that provide a 4mA-20mA signal. Both properly transmit within that range. I have 2 DAQ1400 units plugged into 2 ports on a HUB0000. When I wire the first transmitter up to the first DAQ1400, everything works. But as soon as I connect the second transmitter to the second DAQ1400, I lose one transmitter and only get readings from the other.

Does anyone have a solution to this, or at least insight as to why I cannot have 2 pressure transmitters connected to two DAQ1400's attached to a VINT Hub?

This is likely an issue with current draw causing a drop in USB supply voltage. This then causes issues in the measurements, likely causing saturation. Attach an error event to the CurrentInput object and check if you are getting saturation errors events. If so, the best possible suggestion is that, assuming you are using the 24V supply from the DAQ1400, if possible run it at 12V instead. That will greatly reduce the current consumption. Also providing a stronger USB supply voltage by using a powered USB Hub may help the issue as well.
If possible, attach the datasheet for the sensor you are using so I can take a look at it.

Thank you for your suggestions. I am attaching Dwyer Series 605 Magnehelic Differential Pressure Indicating Transmitters to the DAQ1400's and the power supply is a MacBook Pro laptop computer and I am running everything at 12v.

I believe I identified a problem with one of my Indicating Transmitters as the current output is fluctuating significantly and could be causing other problems. I have ordered a replacement, and in the meantime, I will try swapping in another pressure indicating transmitter to test if indeed the bad transmitter is the culprit and post my results later today.