Analog Input 0-10V needed...gain diminishes at 5V

[Robhincks]

I am using a pressure transducer to calculate the height of water in a tank, the output is in the form of millivolts and is being amplified, the max voltage reading being sent to the analog input in 9.3V.

The system works fine until a value above 5V is sent to the daq, after 5V i lose my gain,  I have the voltage input setup within daq assistant set to -10+10V. however the problem remains the same, Does anyone know how to set the range to 0-10V.

any reply greatly appreciated.

Specs: NI-USB 6008

[aeastet]

How did you set up this channel to read? That are many ways to do this and we need to understand what you did to help.

[JÞB]

Why are you not reporting the water tank's "Height" (Volumn, weight, or whatever)  It seams as though all you need to do to calculate the information of interest is a "DAQmx Scale" to translate your mVolts into much more useful units!

Those "Scales" do not need to be linear.  HECK they do not even need to be static!  (If the mV / meter of H2O scale changes with Temerature just read Temerature and adjust "Scale") 

In short;  Scale your DAQmx input into units of interest 

[NIquist]

Have you verified this gain drop with a voltmeter?  Unless your 6008 is very broken there's no way it's loading down your measurement.  It does not matter what DAQ parameters you have set in software.  The worst that can happen is you get a clipped signal.  The high impedance analog IN of your 6008 will not load down your signal.  Either something in the amplifier circuit is wrong or your sensor is not linear and you need to scale it properly as was mentioned above.

EDIT:  Hmmm, I could be wrong.  I just checked the specs after realizing how low-cost the USB-6008 is.  It has quite a low input impedance of 144Kohm.  That's compared to the 10Gohm impedance I'm used to with the M and X series DAQs.  Sooo, depending on the output impedance of your amp, you just might be loading your signal down.  You may need to modify the amp or add a buffer circuit to match the impedances.