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I am working with a Dataq DI-1100 whose specs tout:

"The analog inputs offer a fixed measurement range of ±10VFS..."

VFS looks like a unit, but I find the language confusing. Researching turns up statements like,

"where VFS is the full-scale input voltage that is determined by a reference voltage"

My training is in mathematics. A range may be given with a unit, such as voltage, and the fact that an interval is given clarifies that the values obtained will lie between the interval's min and max. I would expect the statement to simply say "a fixed measurement range of ±10V".

Is VFS indeed "voltage full-scale" and, if so, is there more to "full-scale" than simply the interval of possible values?

Lorem Ipsum
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2 Answers2

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It means "volts full scale".

So your Dataq unit is able to measure voltages between -10 and +10 V.

And if it is, for example, a 12-bit ADC, then each 1-count change in the digital value corresponds to $$\frac{20\ V}{2^{12}-1}\approx 0.00488\ V.$$

is there more to "full-scale" than simply the interval of possible values?

No, not really.

The Photon
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"Full Scale" is a left-over from the old analogue meter days.

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Figure 1. An analogue multimeter scale. Source: Design World Online.

I would expect the statement to simply say "a fixed measurement range of ±10V".

That's reasonable. The idea here is that a sensitive meter movement was used to measure a range of voltages, currents and resistances as indicated on the scale of the meter. The meter movement itself was very sensitive - maybe 0.1 mA would cause it to swing to full scale (there it is again!).

By connecting resistances in series with the coil it could be de-sensitised to allow it to have much higher full-scale voltages. This meter may have had 10 V, 50 V, 100 V, 250 V ranges selected by a rotary switch with interpretation of the reading left to the user who would have to look at the full-scale reading on the meter's selector switch.

Further switching arrangements allowed the same meter to be used to measure current. In this case various "shunt" resistors are switched in parallel with the meter movement to allow most of the current to bypass the meter coil.

In the case of a digital measurement device it will have a certain number of bits resolution. The "full scale" voltage is that which gives the maximum digital count on the input.

Transistor
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