SilentScreamer
Senior Member
That is the one, I'm currently designing it to have a gain of 10 rather than a gain of 100 and a non-inverting amplifier on the output with a gain of 10 as you suggested.
Measuring Small Voltages
- Thread starter SilentScreamer
- Start date
silent screamer: many here have good ideas, Dr. Acula wrapped it up pretty well. To understand accurate shunt use and why the diff amp is so valuable,
consider expensive 5 and a half digit DVM's, like a Fluke or HP. For up to 10A
you can use the jacks on the front, going to your load, to measure DC current.
But for more accurate results, eliminating the voltage drop in the leads which is an error, you can use a Kelvin conn. All this means is that there are 2 additional leads, the sensing leads, that clip directly across the load or shunt. These sensing leads DO NOT have the load current going thru them, so there is no voltage drop error in the measurement. That is what we are trying to get you to do with the diffamp, you need a bipolar input to the amp. Normal opamp amps with a single input use the chip ground reference are not good for this.
With the tiny 50mV drop you have for full scale (can't you used a bigger shunt r to get more volts?), you made this a tough problem.
consider expensive 5 and a half digit DVM's, like a Fluke or HP. For up to 10A
you can use the jacks on the front, going to your load, to measure DC current.
But for more accurate results, eliminating the voltage drop in the leads which is an error, you can use a Kelvin conn. All this means is that there are 2 additional leads, the sensing leads, that clip directly across the load or shunt. These sensing leads DO NOT have the load current going thru them, so there is no voltage drop error in the measurement. That is what we are trying to get you to do with the diffamp, you need a bipolar input to the amp. Normal opamp amps with a single input use the chip ground reference are not good for this.
With the tiny 50mV drop you have for full scale (can't you used a bigger shunt r to get more volts?), you made this a tough problem.
BeanieBots
Moderator
Oh, sorry. No idea. Never met the 1NA217 amp. Couldn't comment on it's suitability for current sense measurements.
However, you will require whatever gain is required to bring the sense voltage up to 5v.
My comment about using two stages was assuming a more 'normal' op-amp. (eg LM324).
When designing a differential amplifier for high-side sensing, the resistor values become VERY critical. For high-side I'd suggest a proper high-side sense amplifier such as the (now obsolete) MAX471.
For low side, a simple two stage high gain amplifier such 1/2 quad LM324.
However, you will require whatever gain is required to bring the sense voltage up to 5v.
My comment about using two stages was assuming a more 'normal' op-amp. (eg LM324).
When designing a differential amplifier for high-side sensing, the resistor values become VERY critical. For high-side I'd suggest a proper high-side sense amplifier such as the (now obsolete) MAX471.
For low side, a simple two stage high gain amplifier such 1/2 quad LM324.