It’s actually a Down Under opamp. Its CMR extends about 200 mV below its negative supply rail. (From my faulty memory).

 

It’s actually a Down Under opamp.

Okay.
But extrapolating from the Over-the-Top designation, shouldn't it be an "Under-the-Bottom" op amp?

 

This is an easy way to make any Op-Amp work ...........
.
.
.

 

This is an easy way to make any Op-Amp work ...........

Works as long as you don't mind having to adjust the zero output with a pot, and the lower common-mode rejection to changes in the supply voltage.

 

The Trim-Pots are only for Bench-Setup,
to keep the Input, and Output, Voltages comfortably within the capabilities of the cheap-Op-Amp,
then they may be permanently replaced with the appropriate Resistors.

There are excellent Chips purposefully made for this exact job that have already been "ruled-out".
.
.
.

 

Most of the JFET op-amps will work to 0.6V above the positive rail, but most JFET op-amps don't have a very good DC offset spec.

 

If that "Any Op-amp" scheme were that good, there would be not much market for Instrument Amplifier devices.. But certainly there is. An I.A. is quite different from an op-amp. Really, it is.
I will not argue with those who do not know.

 

The Trim-Pots are only for Bench-Setup,
to keep the Input, and Output, Voltages comfortably within the capabilities of the cheap-Op-Amp,
then they may be permanently replaced with the appropriate Resistors.

If it initially requires a pot, what is the reason to go to the significant effort of replacing it with fixed resistors after offset adjustment (with the limited values of fixed resistors likely leaving some residual offset)?

 

it may also need in-field calibration from time to time.
btw if gal is to measure current in high side, why not used products designed just for that? there is bunch of amplifiers for this purpose (INA, INB...)

 

This is a high-volume "Bean-Counter" problem.
.
.
.

 

it may also need in-field calibration from time to time.
btw if gal is to measure current in high side, why not used products designed just for that? there is bunch of amplifiers for this purpose (INA, INB...)

.
Resistors generally don't require periodic "re-calibration".
You must have skipped-over the part where the TS stated that
super-cheap generic-Op-Amps will be used,
evidently, because of mass-production-cost considerations.

Precision is obviously not a concern in this case.
.
.
.

 

You must have skipped-over the part where the TS stated that
super-cheap generic-Op-Amps will be used,

I must have "skipped-over" that also.
In what post did he state that?

 

exactly. even search reveals only one member using those terms.
TS started with OPA192 that costs at least 3x more than high side sensing IC so this would make things simpler, better, smaller and cheaper.

 

My Bad ........
Or maybe not so much .........
After re-reading,
I could only guess as to why all the back and forth discussion about using the LM324,
add to that, my possible misinterpretation of Eric's #13 Post.

Why so much effort when there are Op-Amps specifically designed to side-step this ancient problem ?
.
.
.