= Measuring chain
A \b[measuring chain] is one successive signal path through a <measuring system>, beginning at a <sensor> and ending at an output element. The VIM illustrates this with both an electro-acoustic chain and a mechanical chain; a <measuring chain> need not be electronic.<International vocabulary of metrology by JCGM>[VIM3entry3.10, definition and examples1–2]{ref}
Consider an original <force> measurement: a <load cell> produces an <electric potential difference>, an <amplifier> scales that signal, an <analog-to-digital converter> encodes it, and software converts the code to a force value. This is one <measuring chain> within the larger <measuring system>, which also includes its excitation supply, references and mounting arrangements. The <load cell> acts as a <measuring transducer>.
In an ideal linear model, let sensor response be $S=2\,\mathrm{mV\,N^{-1}}$, amplifier gain $G=100$, and converter step $q=1\,\mathrm{mV}$ per code increment. If the additive output offset is $n_0=10$ increments, the numerical output is
$$
n=\frac{GS}{q}F+n_0=\left(200\,\mathrm{N^{-1}}\right)F+10.
$$
Thus $n=610$ implies $F=(610-10)/200=3\,\mathrm N$. These are stipulated teaching values, not measured equipment performance.
The example exposes why <measurement calibration> must describe the relevant path. Changing amplifier gain changes the relation between output and force even if the <load cell> is untouched. A saturated stage can also discard information that later conversion cannot restore. Gain uncertainty, offsets, <instrumental drift> and finite conversion steps contribute at different points; treating the final display's increment as the whole <measurement uncertainty> overlooks those contributions.
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