Electronics > Repair
Keithley 2000 TF-245 version / year question
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Kleinstein:
There is no need to go for low tolerances - there is essentially no gain from this. The meter should tolerate quite some deviation from nominal. Even with 0.05% resistors one would still need recalibration as the gain with change a little.  Some compensation is possible by changing R300 if needed.

The point is more with matching between the three ~ 30 K  resistors towards the integrator and the chain with 20K 10K 9K1K from pin 1 to 3. Here it could make sense to use 4 x 10 K as a set with 100 K in parallel to 10 K to get close to 9 K.   ORN / MORN resistor arrays are not that expensive (~ 4 EUR) and usually good matching (e.g. 1 ppm/K range for 10 K).  ACAS would be small and cheap.
Even with seprate resistors it can make sense to have at least the 20 K as 2x10K.
coromonadalix:
would a tf-245 equivalent feasible, is there some companies who can do custom value / part / like this one

will we scrap meters because of this %@ of part ?   that's why i never bought theses series of meters because of that single part ....

i do  hope some substitution will be feasible
Overspeed:

--- Quote from: Kleinstein on May 13, 2024, 04:44:05 pm ---There is no need to go for low tolerances - there is essentially no gain from this. The meter should tolerate quite some deviation from nominal. Even with 0.05% resistors one would still need recalibration as the gain with change a little.  Some compensation is possible by changing R300 if needed.

The point is more with matching between the three ~ 30 K  resistors towards the integrator and the chain with 20K 10K 9K1K from pin 1 to 3. Here it could make sense to use 4 x 10 K as a set with 100 K in parallel to 10 K to get close to 9 K.   ORN / MORN resistor arrays are not that expensive (~ 4 EUR) and usually good matching (e.g. 1 ppm/K range for 10 K).  ACAS would be small and cheap.
Even with separate resistors it can make sense to have at least the 20 K as 2x10K.

--- End quote ---

Hello

Thanks for advises , I will check and sort the resistor I have a kelvin setup for SMD and I can try to adapt a jig for null meter in the aim to control SMD

Question : ppm/C for resistor from the same batch are normally the same OR I need to to make measurement at several temperatures ? my kelvin jig is in controlled temperature enclosure

Setup of resistor : as on the ''top plate roof'' there is room to place a 32 mm x 80 mm PCB  I can use several setup without real problem I can even set a small thermal insulation box and why not an oven if necessary

Regards
OS
Kleinstein:
There is no real need to go over the top with the resistors. After all it is only a 6 digit meter.

With resistor from the same batch one often gets some matching, but of cause not perfect and not guaranteed. Things can also be different between types.
There should be no need for super accurate resistor value matching - if at all it would be TC matching and getting comparable long time drift / PCB stress effects.

For the self heating effect (especially the 30 K at the ADC input) the tight thermal coupling in an array would be an additional advantage over separate resistors.
Still 30 K as an array are a bit tricky (3x10 K or 10 K +20 K).
It is a bit clear if the resistors for the references should be exactly equal or a slight difference (e.g. on the order of 1/128) wanted - whicht way fits depends on how the result is calculated. So an extra series resistor (e.g. ~ 234 ohm) for pin 11 may make sense to have the option to adjust.
Overspeed:

--- Quote from: Kleinstein on May 13, 2024, 07:49:57 pm ---There is no real need to go over the top with the resistors. After all it is only a 6 digit meter.

With resistor from the same batch one often gets some matching, but of cause not perfect and not guaranteed. Things can also be different between types.
There should be no need for super accurate resistor value matching - if at all it would be TC matching and getting comparable long time drift / PCB stress effects.

For the self heating effect (especially the 30 K at the ADC input) the tight thermal coupling in an array would be an additional advantage over separate resistors.
Still 30 K as an array are a bit tricky (3x10 K or 10 K +20 K).
It is a bit clear if the resistors for the references should be exactly equal or a slight difference (e.g. on the order of 1/128) wanted - whicht way fits depends on how the result is calculated. So an extra series resistor (e.g. ~ 234 ohm) for pin 11 may make sense to have the option to adjust.

--- End quote ---

Hello

Ok I make a trial and post the results step by step

Regards
OS
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