This follows on from my question about cleaning a 400 k ohm resistor in a 34970A data acquisition unit, but I thought the tasks were sufficiently general to warrant another thread.
I've replaced a 400 k ohm resistor in what is effectively a 6.5 digit multimeter, as a service note indicates that the resistor can drift, putting the instrument out of specification on the 10 M ohm and 100 M ohm ranges. I bought the resistor from Keysight, as it was the only source of this odd value. As far as I can see, the specifications are 400 k ohm, 1% tolerance, 2 ppm/deg C temperature coefficient. Andreas Jahn mentioned that simply soldering a metal film resistor will change its value by several tens of ppm. I don't know what type of resistor this is. Poul-Henning Kamp wrote "You can bring that down both in PPM and time by a "degauss" temperature-cycling sequence [+N, -N, +(N-2), -(N-2), +(N-4), -(N-4) ...]" I'm not sure how to interpret that equation, or how best to do this with the limited equipment I have available. I don't have any environmental chamber where I can carefully control the temperature. What I do have available to me is 1) Large domestic chest freezer that's not in use, and could be pressed into service to cool something. I believe that cools to about -18 deg C. The operating temperature of the instrument is 0 to 55 deg C, and the storage temperature is -40 deg to + 70 deg C, although storing above 40 deg C decreases the battery life. 2) I could put a heater in the chest freezer, and hook up some electronics so the freezer and heater acts to heat and cool. 3) Switching the unit on makes the internal temperature rise about 5 deg C hotter than ambient, so power cycling the unit will cause a change of internal temperature, but not very rapid and not very much. Since changing the case on this unit, for one that's ventilated, the instrument runs a lot cooler than it used to. Previously the side panels got uncomfortably warm to hold for a long period, but now its almost impossible to see from the side panels the unit is on. So I'm guessing that changing the case, as detailed on a service note, will have reduced the temperature of a lot of internal components quite a bit. -- Dr David Kirkby Ph.D C.Eng MIET Kirkby Microwave Ltd Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD, Essex, CM3 6DT, United Kingdom. Registered in England and Wales as company number 08914892 https://www.kirkbymicrowave.co.uk/ Tel 01621-680100 / +44 1621-680100 _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/volt-nuts_lists.febo.com and follow the instructions there.
