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cDAQ-9178 with NI 9221 connected, signal issues

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I have a cDAQ-9178 with NI 9221 connected taking 3 pressure readings.

 

If a known pressure is applied to any channel, I get 5V 

If the same pressure is applied to 2 channels, I get 2.5V

 

Everything is wired correctly.

 

Could someone point me in the right direction for next steps troubleshooting please? 

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Message 1 of 6
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It sounds like a ghosting issue. Try How Do I Eliminate Ghosting from My Measurements?

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Message 2 of 6
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@ZYOng wrote:

It sounds like a ghosting issue. Try How Do I Eliminate Ghosting from My Measurements?


They're not adjacent, the channels are currently separated (using 0, 2 and 4) with 1 and 3 being left blank. It was previously connected to 0,1,2, but I spaced them to try and prevent any ghosting. 

Setup is 3 x 1Bar pressure transducers on a 10V supply, max 5V output. 

Sample rate is 1Hz Sample size 1

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Could you please explain the connections and how you apply the signal?

Santhosh
Soliton Technologies

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@santo_13 wrote:

Could you please explain the connections and how you apply the signal?


Each pressure transducer has a 4 pin connector. 

1&2 are 9-32Vdc supply voltage pins.

3 is a +ve signal output

4 in earth. 

 

1+2 connected to uninterruptible power supply currently set to 10V

3 is connected to ai0 (and ai2 & ai4 respectively) 

4 on all three are commoned into the ai9 NI9221 ground connector

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Message 5 of 6
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Solution
Accepted by topic author LVIEWPQ

So it would appear that it's a fault with the the grounding on the NI 9221.

When connected to the supply ground, instead of the NI 9221, the ghosting disappears. 

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