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NI 9207 Voltage Drop When Current Added

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Hello,

 

I have an NI 9207 DAQ card that I am using to measure voltage and current from an experiment. I have read before that when the current is added, it influences the voltage. I saw this happen, my voltage dropped the moment I connected a current to the card. I have read that there is a way to measure one at a time to prevent this drop, but I am not sure this is possible since I see the drop the instant I add the current. Is there anything that can be done to prevent this drop from happening?

 

Thank you for your help.

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Message 1 of 12
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Give us a description of the signal source(s)

 

That would make our responses much easier. 


"Should be" isn't "Is" -Jay
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Message 2 of 12
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Hi Jay,

 

I have a 0-5 VDC voltage source from one sensor that shows the correct voltage in LabView when I have it connected to the first port (ai0 and ai19). When this is the only thing connected to the 9207 card, the voltage displays the values I expect in LabView, it also works properly when more voltage sources are connected to the first 8 ports on the card. However, the card also has the 8 ports for current. The moment the current is connected to the card, the voltages drops. The picture included with my previous post shows this voltage drop. The current is a 0-20 mA current and is connected in ai8 and the COM. I believe I should be able to read both the voltage and the current from this card, but I am not sure how since the voltage drops as soon as the current is added. If there is any other information I need to add, let me know. Thanks for your help.

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Message 3 of 12
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Hi Dylan,

 


@DylanP wrote:
If there is any other information I need to add, let me know.

What about a electric schematic of all the wiring in your setup?

Please draw all voltage/current sources, all wires, all sensors, and your DAQ device in this schematic!

Best regards,
GerdW


using LV2016/2019/2021 on Win10/11+cRIO
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Message 4 of 12
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Hello,

Here is a schematic of what I have hooked up right now. The voltage drop occurs in the same manner whether I have one current source or more. Adding more doesn't make the voltage drop any further and adding more voltage sources the voltages are dropped the same way. For instance, if I have a 5 V source, it drops to a 4 V source when the current is added and adding another 5 V source will show as a 4V source as well.

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Message 5 of 12
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Could you please be more specific about the sensors and power supply involved? like the model and make, maybe a link to the manual/spec sheet?

Santhosh
Soliton Technologies

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Message 6 of 12
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TDK Lambda LS25-24 is the power supply. The sensors data sheets are attached. My flowmeter has the 0-5VDC output.

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Message 7 of 12
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Solution
Accepted by topic author DylanP

Your connections are correct except for the 0-5V signal you did not connect it to COM as suggested in the user manual

santo_13_1-1646176049082.png

 

Santhosh
Soliton Technologies

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Message 8 of 12
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@DylanP wrote:

Hi Jay,

 

I have a 0-5 VDC voltage source from one sensor that shows the correct voltage in LabView when I have it connected to the first port (ai0 and ai19). When this is the only thing connected to the 9207 card, the voltage displays the values I expect in LabView, it also works properly when more voltage sources are connected to the first 8 ports on the card. However, the card also has the 8 ports for current. The moment the current is connected to the card, the voltages drops. The picture included with my previous post shows this voltage drop. The current is a 0-20 mA current and is connected in ai8 and the COM. I believe I should be able to read both the voltage and the current from this card, but I am not sure how since the voltage drops as soon as the current is added. If there is any other information I need to add, let me know. Thanks for your help.


I hope you typeod! ai0 and ai8 are a differential pair.  ai0 and ai19 are not.


"Should be" isn't "Is" -Jay
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Message 9 of 12
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Hi Jay,

 

No, I did not typo. ai8 is the first +- 20mA current channel and is not the negative terminal to ai0. For the voltage, ai0 is the +V and ai19 is the -V. This can be confirmed in LabView where it shows how wires should be connected for a voltage input or current input. This can also be seen in the wiring schematic I provided that shows ai8 connected to a resistor for measuring the current.

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Message 10 of 12
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