On Wed, 26 Jun 2019 at 06:05, Poul-Henning Kamp <[email protected]> wrote:
> -------- > In message <[email protected]>, Andreas > Jahn wri > tes: > > >you know that even a metal foil resistor can drift several 10 ppms due > >to soldering? > > 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) ...] > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 The description of the resistor on the Keysight website is Resistor-Fixed 400K Ohm +-1PCT 0.25W TC+-2 thin film THT I assume that it 400 k, 1%, 0.25 W, +/- 2 ppm/deg C, thin film, but I don’t know. The resistor fitted looks like one of the expensive Vishay 0.01% resistors I have around here. Given the instrument is about 20 years old, it has crossed my mind whether I am better leaving the original resistor in place, despite I have have bought a replacement from Keysight - the only source I could find of the 400 k ohm value. I assume from your equation you mean heat the resistor a little, cool it a little, then heat it to a higher temperature , then cool it to a lower temperature. Unfortunately I don’t have any environmental chamber. The only thing I could realistically do is to power cycle it every 15 minutes whilst leaving it in an unheated garage. At night the temperature would probably fall to around 15 deg C and during the day it would probably reach 25 degrees C. That’s not what your equation suggests, but it is probably about the only way I have of causing temperature changes. The temperature inside this data acquisition unit will charge when I next power it on as I have replaced the enclosure for a ventilated enclosure and replaced the fan for a different type. Those changes are suggested in one of the service notes. The unit has internal temperature sensors for cold junction compensation of thermocouples. Apparently the changes to the case and fan improve the cold junction compensation. I am amazed that the original enclosure design works at all as the outlet of the fan is a couple of mm from the side panel of the case, which has no ventilation holes! I don’t know who could have thought of that bright idea. The new case has ventilation holes right by the fan outlet, as well as a number of other ventilation holes. The shape of the impeller on the new fan is different from the original fan. The fan is very small - around 40 x 40 x 8 mm from memory. Dave. -- Dr. David Kirkby, _______________________________________________ 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.
