analog in voltage draws too much current

[Eric-APU]

Hi,

    I am using a PCI 6030E multifunction DAQ board for a multitude of purposes in my current application. Most of it works perfectly, but I am controlling several power supplies using this board through the AO voltage. This works fine, but the PS's supply a 0-10 V output indicator of the voltage that is being produced (0-100% of the total output, in this case 30 kV). When I measure this voltage with a multimeter, the voltage is exactly right (I see 1.66 V for a 5 volt output), but when I use the AI voltage functions, I get much lower values which decrease with time. I believe this is a current problem, the PS indicator uses a 10 kohm resistor to protect the circuitry from errant voltages applied to this channel, so I have a maximum of 1 mA. If I sample at a lower rate (1-2 Hz), the values rise closer to that which I would expect, but due to the timing of the system, I cannot go any slower than this. I believe the DAQ system is simply drawing too much current and so a voltage drop is seen, but do not know how to correct this problem. Any suggestions? Below is a screenshot of the code I am using to view these voltages.

<>< Eric 

 

[johnsold]

Eric,

The input impedance is specified as 100 GΩ in parallel with 100 pF when the device is powered on.  So it is unlikely that loading is the issue.

Are you connected single ended or differential?  How are grounds connected?  I suspect a connection or grounding problem is much more likely.

Lynn 

[Ben]

A non-damged board should have input impeadance on the order of meagohms or more.

Check your connections.

If you still have trouble, draw up you connection diagram (complete with pin numbers and model numbers) and post that image and info.

Someone may be able to help after seeing that info.

Ben

[Eric-APU]

I am currently connected single-ended (I think, the lead coming from the power supply (a glassman FC series HV power supply, 0-30kV) is connected to pin 58, or AI 14 for the PCI-6030E board, I dont have a negative lead). This supply is grounded to a common going out to the building ground. I am not very familiar with electronics, so any help on how this is incorrect would be greatly appreciated. Thank you for your responses,

<>< Eric 

[Ben]

Please have someone help you draw up the circuit.

Trying to trouble-shoot an electrical problem using words only is like trying to comunicate the pythagoriam theorum using only words.

Ben

*Sure the Scarecrow got pretty close but that was only after he got his brain.

[LV_Pro]

I agree, have someone sketch the hookup. You say that you are connected single-ended with only one wire, does this mean that you don't even have a common ground for the DAQ unit connected? Looking at the web site for that company it appears that J3 is the connector with the V monitor signal, and there are pins marked ground, and common. I suspect that one of those is the required "return" path for the monitor signal. It is usually not a good idea (would say never, but ...) to use "earth" grounds for any measurement signals, there are too many unknowns, sources of noise.

[Eric-APU]

I just tried using the common connector on the HV wired to the AIGND terminal of the SCB-68, to no effect. A sketch of the connection (crude and simple, I know) is below, this is all of the connections that I have. I have also added the connection diagram for the power supply for reference. Thank you for your help,

<>< Eric 

[Ben]

Double check your connections!

You said AI14 but your codes hows AI 13.

I don't see in the code where you are specifying single-end so it may be defaulting to differntial.

I tried looking at your images but they are so small I can't read them... does that show AI1 ?

Another thing that can help you with the modern versions of LV. Goto MAX (measuement and automation explorer) and find your device and use the test panels to test out the AI without any code. Modern version of MAX will also show you a picture of how to wire the circuit.

Ben

[Eric-APU]

It was in Differential mode. Changed to RSE, and the problem was solved. Thanks for your help!

<>< Eric 

[hecmar.arreola]

Please be careful!  You say you don't have any experience with electronics and that makes me a little nervous considering you are playing with a 30kV supply.  Isolation transformers are your friend.