DAQ reading problem
DAQ reading problem
(OP)
Hi,
I am using a DAQ board to read the voltage across a load cell to a computer. I also have a 2.2-2.5GHz power amplifier sitting close to the DAQ board. My problem is when the amplifier is on, my DAQ reading to the computer shifts about 6mV, which means with nothing attaching to it, my labview program shows the load cell has about 5 lbs force! But there is no change before or after turning on the amp if I use a voltmeter to measure the voltage at the DAQ board directly. Any suggestion is appreciated.
I am using a DAQ board to read the voltage across a load cell to a computer. I also have a 2.2-2.5GHz power amplifier sitting close to the DAQ board. My problem is when the amplifier is on, my DAQ reading to the computer shifts about 6mV, which means with nothing attaching to it, my labview program shows the load cell has about 5 lbs force! But there is no change before or after turning on the amp if I use a voltmeter to measure the voltage at the DAQ board directly. Any suggestion is appreciated.





RE: DAQ reading problem
The first thing to try is to separate them and see if that gives enough improvement; more distance reduces coupling effect typically.
If you twist the wires running to the load cell that will help to cancel out some coupling. Same thing goes for the power supply wires for the PA, if applicable.
You might also need to put a choke on the power supply leads. Stward has some nice ones that will clamp on the cable, and some good app. notes to explain why you are doing this.
If you can do it safely, isolate the load cell or the PA from GND. If there is a DC path between the two you may be forming GND loops that can also cause offset voltages.
Welcome to the world of EMC/EMI!
RE: DAQ reading problem
If this is a USB based DAQ card, they are tradionally more susceptible to picking up EMI/RFI than cards residing within a PC.
Your DMM may have filtering, averaging, or better CMRR than the DAQ. Also, the sampling rate of the DAQ may make it display more noise than the DMM.
Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.
RE: DAQ reading problem
My DAQ is now working as single-ended-nonreferenced mode. Is it easy to change it to differential mode?
RE: DAQ reading problem
RE: DAQ reading problem
I managed to configure the DAQ to diff mode this morning and now I have no problem with the load cell anymore. Thank you guys for the help.
bj
RE: DAQ reading problem
Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.
RE: DAQ reading problem
i.e. as opposed to RF coupling being the problem. There wasn't any mention of a signal in the RF amp, just that it was turned on.
Any thoughts?
kch