Setting a Temporary Gain Calibration Using a Precision Reference
AgilentTM 34461A Digital Multimeter
A tech note in progress ... revised 7/31/2013
Before describing a practice tip I use with our new Agilent 34461A, it should be emphasized that we have no affiliation with Agilent and that Agilent might not approve of this practice tip. I use the calibration feature without saving the new calibration values. If you accidentally save your temporary calibration values, you will likely void your one year Agilent calibration.
Our understanding is that performing a calibration operation on one scale without saving the results does not in anyway damage the unit or cause damaging wear. However, we are not responsible for any negative consequences of using our practice tip! (no liability whatsoever!)
As many of you know, I spend a great deal of time working at our 10 V calibration point. Our in house transfer standard is a FLUKE 732B which has been in the FLUKE calibration system for many years now.
I am extremely impressed by our new 34461A. It is an absolute joy to work with. However, our unit has a now measured temperature coefficient of about 1 ppm / degree c (about 10 uV / degree c on the 10 V scale). During the summer, I often enjoy days with the lab windows open wide. While room temperature can be relativey stable over an hour or two, there can be wide swings morning to evening and day to day. Fortunately the temperature coefficient of the 732B is less than 0.04 ppm / c. Also, we use our micro-environmental chamber for calibrating reference boards with its own thermo electric heat pumps and ILX 5910B temperature controller.
During our first weeks with the 34461A, I used the null feature to "slew" in 10 V exactly using an offset of from about 20 uV to 60 uV as needed. The rigourous correction should be a gain trim, not an offset correction, however for "single point" work, and tens of uVs of shift the difference in methods is not detectable.
I realized that like the 34410A, one can calibrate a given scale and NOT save the new calibration constant. Actually, at least one of our 34410A DMMs has very near a zero temperature coefficient near room temperature and I just calibrate the 10 V scale and save the calibration constant. (Caution, we do not know what effect changing the 10 V scale calibration (and saving the new values) might have on other scales).
So, here it is - 34461A Practice Tip: (Use at your own risk, no affiliation with AgilentTM)
It occurred to me that one can easily set a temporary gain calibration on the 34461A by performing a single point calibration and NOT saving the new calibration values. If you do not save the new calibration values, the calibration count does not advance. If you power down and power up again, the temporary calibration values are gone, and the factory calibration is intact.
After banging my head against the table top several times, I finally learned that to do a 10 V DCV calibration, you also must perform the - 10 V DCV (negative 10V) calibration step (it's not in the manual!). After that, it works perfectly! For temporary use, do not save the calibration constants!
For operation over some limited time period with limited shift room temperature, this practice looks like a huge time saver for us. We use the 34410A (the "10A" not the "01A") for most calibration operations, often as a HiZ null meter with the 732B. However, when I set the 34461A to the 732B, either by null or by this practice tip, the 34461A provides a wonderful final calibration check. Using the histogram display set to +/- 5 or 10 ppm (+/- 50 to 100 uV) gives a wonderful final check of low frequency noise. Also, the large numeric display is so easy to read and work with, both for a quick final check and for recording our trim jumper out value for our SVR transfer references.
GELLER is NOT responsible for any negative consequences of using our practice tip! (no liability whatsoever!) GELLER has no affiliation with Agilent.
COPYRIGHT © 2013 JOSEPH M. GELLER