The data sheet specifies V(os) of +/-20mV typ., +/-50mV max. It also
shows a V(os) which is very dependent on temp (+/-0.2mV/degree C) and
supply voltage (+/- 2mV/V). This is not good news if you're looking
for precise control of offset voltages in a DC/low frequency signal
application.
If you're going to stick with the INA124 (it is lower cost than the
alternatives), you might want to use a unity gain op amp with an offset
adjust at either the input or the output side. One other way would be
to use a multi-pole reed relay and a sample-hold setup to achieve
chopper stabilization, but that is almost certainly more trouble than
it's worth here.
If you want to deal with the stability and drift problem, though, you
might want to upgrade to the Analog Devices AD202. It's more
expensive, and has lower bandwidth, but if you've got +15V on the
receiving end, it will give you better offset, stability and drift
figures, and also gives you a free +/-7.5V supply at the signal end.
Also, since there's an op amp signal input, you can build in your
offset adjust more easily. I've used it successfully many times.
There is one other thing, which I'm not sure is really relevant in your
case. The AD202 is transformer isolated, which might give you more
reliable protection than the capacitive isolation of the ISO124.
However, that doesn't make much difference in most cases, and the
ISO124 is rated to 1500VAC. It may be at least partly superstition,
but I just feel more comfortable with transformer isolation from a
reliability standpoint as well as a safety one when dealing with
dangerous differential voltages.
http://www.analog.com/isolation_amplifier.html
Good luck
Chris
