[volt-nuts] Mickles 7081 drift issues, some ideas.
m1k3k1 at hotmail.com
Thu Jan 17 22:20:37 UTC 2013
I have been looking at the documentation and circuits of the 7071/7081 and I think you have overlooked something.
According to the manual, if nines=6 or greater then drift=off does not do anything.
Also looking at the large tempco that you had I suspect that the reference zener had drifted enough that the minimum drift current setting was now incorrect for your unit, you should have been able to correct the drift by tinkering with the current setting number, and not by adding copper at +3700ppm c-1. OR the current delivering circuit had changed enough that the zener current was wrong. They are designed to have a minimum tempco at approximately 7.5mA, but for any individual item it may be different from that current.
I used to be a service agent for Dranetz and their 305c's used a reference that was good for 6 to7 digit stability using the in829's and the required current could vary quite a bit. There was no particular use of any high stability resistors in the reference they designed, but it worked quite well.
More information about the volt-nuts