Good day all,

I have a fairly simple question:

If I measure the voltage across a resistor in a chain of (3) equal resistors to determine the current flowing through it, how can I make the absolute voltage drop ground-referenced? Meaning, if you had (3) serially connected resistors from VCC to GND, and the middle one was being measured, how could I eliminate the voltage offset to ground?

Image attached:


I understand the "current measurement" seems arbitrary since it is ostensibly equal throughout, but this question regards a more complicated project I'm involved in.

Another way of saying this is: "How do I format the differential voltage to be referenced to 0V?"

 

"How do I format the differential voltage to be referenced to 0V?

The usual way is to use a differential op amp circuit (example) or a differential instrumentation amp (example).

An important parameter is to make sure the measured voltage has a common-mode voltage range withing the amps spec value.

 

Good day all,

I have a fairly simple question:

If I measure the voltage across a resistor in a chain of (3) equal resistors to determine the current flowing through it, how can I make the absolute voltage drop ground-referenced? Meaning, if you had (3) serially connected resistors from VCC to GND, and the middle one was being measured, how could I eliminate the voltage offset to ground?

Image attached:
View attachment 324037

I understand the "current measurement" seems arbitrary since it is ostensibly equal throughout, but this question regards a more complicated project I'm involved in.

Another way of saying this is: "How do I format the differential voltage to be referenced to 0V?"

First you measure the voltage from the junction of R2 and R3 to ground. Then you measure the voltage from the junction of R3 and R4 to ground. You then subtract the second reading from the first to get the voltage across R3.

 

That is a trick question!! Voltage readings are all relative to the defined point of reference. For the circuit in post #1, the reference point for the voltage across R3 is the bottom end of R3. Without measuring the voltage at an end of R3 relative to "ground" the very best possible is to GUESS that the resistance of R4 is exactly the same as the resistance of R3., AND that no current is flowing elsewhere from the junction of R3 and R4.