I am encountering a situation in which the
tester is reading 270 ohms, but 9 parts out of
500, 000 have been returned to us by the customer which read 230 ohms. I run them thru the tester again, and they 230 ohms.
Can anyone guide me to understand what casuing the resistor to change value ( It is a precision resistor with +- 1% specs. )

 

Wrong packing?

 

What type of resistor is it?
Is the first measurement done at higher temp.?
Are you also manufacturing different resistors in the same machine? Wrong programming code in the machine? May be the operators using old settings?
When was the last calibration done in the machine? Is it too much (wrong) offset for measurement probe resistance in the machine?
I think is more of human error in setup or despatch.
Best luck.
Sekar

 

Mismarked or electrical overstress. Some film resistors suffer from migration with too much voltage or flashover leaves tracks. At these
resistance levels you can almost rule out conductive contamination. Gross overtemp might do it as well but I assume you would see the
evedence from this. Bad trimming can make them susceptable.

Regards

cww

 

What is material? Power dissipation capacity?

Exposure to high ambient or self-generated temperatures could affect the resistor's stability (not accuracy). Some materials will experience a permanent increase n resistance. Also, high humidity exposure will increase resistance, but this condition is reversible.

Sounds like job for QC-man, oops, person!

Regards,
Phil Corso, PE
(Boca Raton, FL)

 

Have you ruled out the possibility that the inspections system is not functioning properly? I once worked on a project where the bad part had to go through several cycles before it could be ejected and discarded. The program had a logical error in it so that in a few cases it would scrap a good part, and allow a bad part to continue on.