SCXI-1520 Calibration Techniques

[WhiteKnight]

I have a question about calibration. There are a lot of things that you can do to better calibrate the channels, like null offset calibration, shunt calibration, multi-point calibration, etc. What is the difference between doing the offset and shunt calibration under the Device tab in MAX and the multi-point calibration under the Calibration tab? When do you need to do a shunt calibration?

[griffindore]

Hi WhiteKnight,

The SCXI-1520 User Manual describes the Offset Null Compensation and Shunt Calibration on pages 4-26 to 4-28 (pdf page 74 to 76). In short, the Offset Null Compensation adjusts the readings so that you receive 0V when the sensor is at rest. The shunt calibration is used to adjust the gain for your readings so that you receive accurate readings when the sensor is not at rest. Make sure you perform the Offset Null Compensation before Shunt Calibration. As you may have already noticed, the Shunt Calibration does not compensate for nonlinearities as it only sets the gain. You can use the multi-point calibration to achieve even more accurate readings after performing both Offset-Null Compensation and Shunt Calibration as the multi-point calibration will help account for non-linearities and remaining error. I hope this information helps!

Message Edited by lion-o on 08-20-2008 11:04 AM

[WhiteKnight]

Okay, but do you really have to shunt calibrate and offset the channels every time in MAX? Isn't there a way to calibrate the actual physical channel so that I wouldn't have to multipoint calibrate or shunt calibrate the channel?

[dansch]

Hi WhiteKnight,

How often you perform the null offset and shunt calibration is really dependent on how accurate you wish your measurements to be. Ideally, you should perform this calibration before each measurement, to account for any changes in temperature or any other circumstances at the time. The SCXI-1520 User Manual contains instructions for performing these calibrations both in MAX and in LabVIEW. Additionally, you will find LabVIEW examples which acquire strain data and perform the calibration programmatically. An example of this functionality may be found in the Example Finder (in LabVIEW under Help » Find Examples) by navigating to Hardware Input and Output » DAQmx » Analog Measurements » Strain » "Cont Acq Strain Samples (with Calibration).vi". Hope this helps,