The 1 A range would likely need switching with a mechanical relay. The leakage than would not be a problem and one may also consider a realy for the 100 mA range.
Exactly my thought, although for the 100mA range the Photo-MOS relay might be ok depending on the personal requirements
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In theory it would be best to use latching relays to avoid additional power dissipation. Could this lead to problems at start up, because effectively one will end up with an undefined state?
Already the 100 mA range shunt gets quite warm and really should be large size, so more like a heat sink mountable power resistor like the PBH series.
8 film resistor in parallel may work, if there is plenty of spacing (e.g. 10 mm) in between, but this would add trace resistance and would thus need extra copper. 0.5 W is quite some heat for a precision shunt.
Probably true, especially with heatsinking (tempco of those resistors isn't always all that great, partially as bad as 50ppm if I remember correctly). Then again, if I'm really going to build this (which I really want to try), I'd be very restricted regarding board height for the analog board (<2 cm), whereas length/width don't matter that much. Therefore I'd probably end up with SMD solution.
If using the 1 A range one would kind of need a lower burden voltage (e.g. 0.5 V range) and lower noise amplification (especially avoid the 100 K resistors at the difference stage) for the 1 A range and likely use this also for the 100 mA range.
Yes, for the reasons discussed I'd propably end up using another array of 1206 10ppm 0,4W (something like 4 strings with 2 resistors each), 0,5 Ohm total. I think since the 1A range is a somehow just a bonus, it wouldn't be too bad if the performance was slightly worse. I'd likely also use a buffer and 10 k resistors for the amplifier. Maybe one could get away with using the Low Range for the FDAC (setpoint) and the x8 Gain of the AD7190
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No idea how much "precision" would be left, but that way, no addtional hardware would be required.
However, the main difficulty (to me anyway) would be the lower voltage/high current amplifier design itself, I think.
The ACASA resistor networks may work, though also not the best performance. There are multiple alternatives for the resistors, including ready made difference amplifiers at places.
Yeah, there are certainly even better options, but value per money is there, I think. If I do my own layout, chances are high that this will be the main weakpoint (starting with simple prototyping mistakes, best practices, ...). (Although I'm an electrical engineer, my work has always been completely unrelated to electronics, metrology aso.; hence I consider myself a advanced beginner).
If you're refering to INA ICs: I haven't found one, that has comparably
- low input bias current
- low offset drift
- supply voltage ratings
- available in diy-friendly packages
all at once (and also, it has to be available in that package). But I'm open to suggestions. As a side note: I'm aware that I can't just compare all datasheet values of an INA with an opamp, because the circuit of 3 opamps will obviously different from one single opamp. However, very many INA have input bias currents in the 1nA range, which I find quite high for obvious reasons
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Thanks,
Sebastian