Problems with Analogue Voltage Inputs

[Thomas Hunting]

Hello Everyone.

I am kinda embarassed here. This is a simple question

.

I am trying to read an anologue input voltage to reflect transformed phase voltages from a 3 phase machine.

When I try to configure the channel the inputs seem to be all high (5V), using labview, though there is no voltage on the terminals.

I am using the DAQ assistant to configure the channel.

I have tried several things and cannot resolve this. I have LAbview 7.1, and a 6025E card.

Can anyone please help.

Thanks for your time.

[Deepu]

Hi Thomas,

I think your question is not very clear!

It would be good if you could post more details like the ports you are using to take the measurements and expected voltage max and min levels etc.

Regards...

[Thomas Hunting]

My apologies. Thanks for the reply.

I am using initally the ai0 channel, which is terminal 3 on my card.

I am reading a 0 - 250 V signal, which I have scaled to an 0 to 5 input signal using an external voltage transformer.

The input to the card is 0 to 5. When I look at the channel with nothing attached even, Labview is reading 5V, even though there is no voltage on the terminals.

I have set the limits at a minimum of 0, and a maximum of 5V.

Regards

[Henrik_Volkers]

Read the manual about bias current(s) on your input

Open channels can drift to any possible input voltage if they don't have a current path for the bias current.

[Thomas Hunting]

Thats done it!

Once I wired the inputs I was able to capature the waveforms correctly.

Thanks for the help.

Regards

Thomas