Aquiring Analog Input

[EECSintern]

Hi everyone,

I am trying to measure an input voltage from a dual sensor vacuum gauge that outputs a voltage in a range from 0 to 10 volts depending on the gauge's reading. I am using Labview 7.1, Daqcard-6024e, and SCB-68 connection box. I am using Daq Assistant and analog input channel 0, but I am getting fluctuating and erroneous voltage readings when the gauge is outputting a steady constant voltage for each value. I have never used Labview before and I think im having a problem with the settings on Daq Assistant or maybe i'm not wiring the output voltage to the connection block correctly. Any help appreciated. Thanks in advance.

[Neville D]

What is the value you are reading? Hopefully it isn't too small.

try using NI-MAX to see if the value reads correctly, before using your own code.

How have you connected the Inputs? Read up on Referenced Single-Ended, Non-Referenced Single-Ended and differential connections. Use differential connections for best noise rejection.

N.

[mross]

QUOTE (EECSintern @ Sep 9 2008, 06:04 PM)

SNIP

maybe i'm not wiring the output voltage to the connection block correctly. Any help appreciated. Thanks in advance.

You need to get the sensor wired up right. Whatever the test panel in MAX shows is what the voltage really is.

In the article linked below look at the business about grounded and floating signal sources. You need to find out how the sensors are grounded. Differential is always preferable if you have a choice.

http://zone.ni.com/devzone/cda/tut/p/id/3344 (Field Wiring)

Even if you get all this right you can still have problems with noise on the signal lines. I had to put a dedicated ground rod into our lab floor to get my equipment off of the building ground which was really trashy.

You need to ground all your equipment properly. Use shielded cable and only ground one end of the shield so as not to create ground loops.

Here is another useful article.

http://zone.ni.com/devzone/cda/pub/p/id/262 (Five Tips)

G/L

Mike