# Resistance measurement Question

#### demisboy

Joined Oct 12, 2021
2
I have a copper winding with known voltage flow of 100V from the distribution network.

I am trying to figure out a way to monitor the resistance variation of this circuit, that is constantly electrified, through a PCB as I must be able to receive a warning when the value increases or decreases over 5% from a specified value.

The voltage flow of the circuit as received by the network is 100V ( 5% error) and the value of the resistance is 0.5Ohm.

I appreciate the help.

#### LesJones

Joined Jan 8, 2017
3,570
You need to provide more information. What do you mean by "voltage flow"? Voltage does not flow. It ie the potential between two points. Currents flows. Post a schematic of the circuit that contains the winding that you are trying to measure the resistance of. Is the 100 volts AC or DC and it it is AC what is it's frequency ? What is the inductance of the winding ? Is the current though the winding constant or is it changing ?

Les.

#### demisboy

Joined Oct 12, 2021
2
You need to provide more information. What do you mean by "voltage flow"? Voltage does not flow. It ie the potential between two points. Currents flows. Post a schematic of the circuit that contains the winding that you are trying to measure the resistance of. Is the 100 volts AC or DC and it it is AC what is it's frequency ? What is the inductance of the winding ? Is the current though the winding constant or is it changing ?

Les.
Hello, the equipment in question is the secondary of a metering voltage transformer so i consider that a schematic will not be needed. You are correct voltage flow was a wrong term, in order to be perfectly clear the transformer in question is a 20kV/100V (AC) with 0.5 accuracy, therefore voltage on secondary varies +/- 5% of 100V AC. The network frequency is 50Hz and the current on the winding has minor fluctuations as the primary voltage of the distribution network is never perfectly stable. The inductance of the winding is negligible.

#### Papabravo

Joined Feb 24, 2006
17,240
What do you think is causing the resistance variation?
I think you are chasing phantoms that do not exist.
I would expect the resistance to change slightly with temperature, until thermodynamic equilibrium is achieved.
You may not think a schematic is necessary, but that is really not your call. If you need help and we ask for it, I kind of think you're obligated to provide it.

#### crutschow

Joined Mar 14, 2008
28,161
To determine resistance you need to measure the current through, and the voltage across the coil, and calculate the resistance from those two measurements.

#### ElectricSpidey

Joined Dec 2, 2017
1,961
I have a sneaking suspicion that the OP wants to monitor the output voltage of the secondary, but doesn't quite know how to put it into proper terms.