= Range-switching hysteresis
\b[Range-switching hysteresis] uses different thresholds for changing from a more sensitive instrument range to a less sensitive one and for changing back. Within the intervening interval, the current range is retained. The selected range therefore depends on the previous state as well as the present <measurement indication>. This prevents small fluctuations near a single boundary from repeatedly triggering <gain ranging>.
A concrete electronic analogue is an <electronic comparator> with two switching thresholds. The primary circuit example specifies upper and lower thresholds of $2.5\,\mathrm V$ and $2.2\,\mathrm V$ and explains why one threshold can produce unwanted transitions with a noisy or slowly changing input. Those are comparator circuit values, not specifications for an autoranging measurement instrument.<Inverting Comparator With Hysteresis Circuit by Texas Instruments>[Design Goals and Design Description, p. 1; switching-threshold analysis, pp. 2–3]{ref}
For an original two-range current measurement, let $H$ denote high sensitivity and $L$ low sensitivity. Use an input-current estimate $x$, expressed on the same calibrated scale in either range. Switch $H\to L$ when $x\ge8\,\mathrm{nA}$, switch $L\to H$ when $x\le6\,\mathrm{nA}$, and otherwise keep the previous state. The hysteresis interval has width $2\,\mathrm{nA}$.
Starting in $H$, the indication sequence $(7.9,8.1,7.9,8.1,5.9)\,\mathrm{nA}$ selects $(H,L,L,L,H)$. A single threshold at $8\,\mathrm{nA}$ would instead select $(H,L,H,L,H)$ and switch at every step after the first. At a steady underlying $7\,\mathrm{nA}$ with bounded readout fluctuations of $\pm0.2\,\mathrm{nA}$, neither boundary is crossed; either previous range remains selected.
The thresholds should lie within the usable overlap established by <range-overlap calibration>. If the two ranges give inconsistent current estimates, a switch can itself move the indication across the opposite threshold and create a cycle. The comparison must therefore use the corrected <measurand> estimate, not identical raw output voltages from different gains.
Hysteresis is not temporal averaging and does not ensure that the new reading has settled. Reserve headroom for a rapidly rising input, reject readings during the required <settling time>, and verify that the less sensitive range still meets its <noise-limited detection threshold>. An input that jumps beyond the current range can cause <amplifier clipping> before the controller reacts, even when its two-threshold rule is correct.
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