When I first plug all of strain gauges in and calibrate them, I get a pop up saying that calibration was successful and the Err% shown for each chaneel is 0.00. When I come back after an hour or two to recalibrate my strain gauges using the same method as before, I get the same message saying calibration was successful, but the Err% has drifted, and they all hover around 8.00-15.00.
From the tutorial I have been using, it states that Err% is:
Err (%)—Percentage offset error, determined by the equation: Err (%) = [(offset value * 100) / (Max Range Limit – Min Range Limit)] where Max Range Limit and Min Range Limit are the maximum and minimum strain range values specified for the given virtual channel.
I am not changing any of the variables such as range when doing the second calibration, yet the Err% changes. Would this drift in Err% be due to external factors such as temperature? When I calibrated for a second time, the calibration still says it is successful. Should I assume that the DAQmx did proper calbiration and not worry about the Err%?
The error percentage of 0.0% is unrealistic (I would expect it up around 0.05% or so) so I'm questioning whether it is doing a proper calibration to begin with. Do you have any way to test it with a known value to see if it is actually off? Also, what hardware are you using?
Julian R. Applications Engineer National Instruments