can not read some kinds of voltage signal by Scxi 1300

[hanwei]

Hi all:

I am just a beginner for NI DAQ, now i am using PCI-6040E, and Scxi 1001 chasis and Scxi 1102 analog input module.

I am wondering why sometimes I can't read some kinds of data from NI by NI Measurement & automation explore software.

for example:

I want collect voltage signals from the pressure transducer, which is just a 2v voltage signal. But I can't get it from NI, (the value is almost 0)

when I try to test other voltage signal from signal generator or battery by same channel, it is fine!

what ' problem about it?   Why Ni can not read some kinds of voltage signal ? anybody konw it?

thanks a lot

[hanwei]

Hi all:

Here I have a question about wiring. In the Pic I attached, must I connect one bias Resistor to the ground? if I want to test a floating signal (like voltage signals (across a resistor) from pressure transducer (4..20mA))

[RT4CY]

Hello hanwei,

I understand you are having trouble reading a voltage from your pressure transducer?  Many pressure transducers are full-bridge sensors, meaning they use internal strain gages.  If this is the case, please check your manual for the required excitation voltage.  You can use our SCXI 1520 module which has an independent 0 to 10 V programmable excitation source for each channel.  Otherwise, you will have to provide your own excitation externally, then scale down to remove the excitation voltage from your signal.  In Measurement & Automation Explorer (MAX), you will create a Custom Voltage with Excitation task to read the voltage from the pressure transducer. 

If you are measuring a floating signal, it is important to provide two bias resistors to provide a path to ground from each lead.  Please see the following Developer Zone article for more information.

Developer Zone Tutorial: Field Wiring and Noise Considerations for Analog Signals

[hanwei]

Thanks for your reply

acutally, I use a external power supply (24v) for pressure transducer.

and I already set up the two bias- resistor for 1 channel, but now the question is one channel is ok, but multi-channel, the voltage value is wrong, (too high).

I post a new question about this one here, and I attach my electrical schematic drawing.

http://forums.ni.com/ni/board/message?board.id=250&message.id=42581&jump=true

thanks again

[BME_genuis]

Ditch the 1300 and get a 1303.  The 1303 does takes care of the noisy floating signal for you via the bias and pullup resistors.