Electronics > Metrology

Why output voltages of precision shunts are so high?

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zlymex:
The output voltage of normal shunts are 50mV, 60mV and 75mV. I thought they may higher at 200mV for precision shunt, but, when comes to precision 100A shunts, why such high voltage of 800mV for Fluke A40B?
http://us.flukecal.com/products/electrical-calibration/electrical-standards/a40b-series-precision-dc-and-ac-current-shunts

Tinsley 4638 @1.0V (100A, 0.01 Ohm), Guildline 9230/100 @1.0V (100A, 0.01 Ohm), even higher.
Transmille 100A @0.7V, Guildline 7340 100A @0.4V.
Ohm Labs on the other hand, produce their 100A shunt at 0.1V only
http://www.ohm-labs.com/precision-shunts/cs-100-300.html

Is that because of the thermal EMF? In theory, reducing the voltage by half will reduce the power and temperature rise also by half, we get the same relative thermal EMF.
Is that because of the thermal EMF at the measurement side? 1 Ohm standard resistor is tested at 0.1V and still
Is that because of the noise or AC measurement considerations?

TiN:
Perhaps old voltmeters were not good at low ranges, so shunts designed to match them were targeted for higher voltage to fit better accuracy?

manganin:
The primary level DC shunts up to 100A have usually 0.1V or 1V output at the nominal current.

Before the long scale multimeters the 1V output was easier to measure (and compare with a standard cell) with the existing equipment. And the 0.1V output is also too low for most thermal converters.

The downside of the 1V output is of course the large amount of heat produced. That is why I prefer my Sullivan 0.001ohm 100A shunt instead of the Leeds & Northrup 0.01ohm 100A.

EEVblog:
Greater signal to noise ratio, less worry about offset voltage in any amp etc. The higher the better, except for the circuit under test.

zlymex:
I guess that too for noise and measurement reason in the old days. However, Fluke A40B-100A is a relatively news device(old model A40A). And the completely new Transmille's 100A, only come out last year?  It is 0.7V full scale.
http://www.transmille.com/bench-instruments/precision-references-and-standards/ac-dc-shunts

Leeds & Northrup also had a 100A version(0.001 Ohm, type 4223).

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