I have three 3478a meters that I plan to sell and was checking the calibration of one against my 3457a using an Agilent USB GPIB adapter. I was plugging the adapter between the 3457a and 3478a as I ran a series of resistance checks using an ESI deca box. Everything was coming out near perfect, many times they matched to the lower resolution of the 3478a. Then all of a sudden the 3478a meter calibration went off the tracks. I thought it was the cable at first, checked it all, then turned it off and on. At that point the meter went 'uncalibrated'. I had the calibration active at the time I was checking the meter. Thinking back, I know it isn't a good idea to swap the GPIB cable while the meter is on but I've done it a lot more than not.
I checked the battery and it is still at 2.95V though I realize it doesn't have much of a load on it. My current plan is to swap the battery and recalibrate the meter to see if it holds calibration. I've had this one a year, it is in great shape, never had a problem, etc. Wondering what happened? USB cable static? Battery? Failing NVRAM (assuming it has one or equivalent). Should I swap the NVRAM (if it has one) before calibration again? I haven't dug out the sheets on it yet to see how the calibration is stored. I would hate to sell it to someone and have it happen to them down the road. What other preventative maintenance can I do to it to limit the exposure of it dumping calibration again?
Thanks