Is there a standard method of schematic design to allow measuring individual resistor values on a PCB? Useful for general debugging, validating a new PCB shop, etc.
Because, if part of your circuit looks something like this:
And you try to measure R1 on the PCB with a DMM, you are actually measuring R1 in parallel with (R2 + R3 + (R6 + R5 + R4 || R9 + R8 + R7)). You could remove the resistor from the PCB, measure, and resolder but this is time-intensive and not scaleable.
My 2 ideas:
- Add a removable jumper on each branch; maybe applicable on a small scale, not so much on a large scale, so the resulting circuit looks like:
Now by disconnecting JMP123, you can measure R1, R2 or R3... Disconnect JMP456 for R4, R5, R6 etc.
- Add a sense resistor in line, perform calculations on live circuit using voltage measurements:
If, somehow, you are able to know with certainty the resistance of RS123, RS456, RS789, you can measure the voltage across them, divide by their resistance to get the individual branch current, then measure the voltage across your desired resistor and divide by the current... However this assumes you know + trust the values given for the sense resistors (RS***)... Alternatively, you could carefully design the pcb trace for a given resistance and measure those 2 points to act as the sense resistor instead.
Interested to see others ideas for accomplishing this.
Related, tangentially: How to measure resistance of resistor in PCB?