UT_TWO_POINT — On/off (hysteresis) controller

A thermostat-style controller. The setpoint order decides the direction, so there's no mode to set:

• OnPoint < OffPoint → fill / heat: on when low, off when high.
• OnPoint > OffPoint → empty / cool: on when high, off when low.

Pins

How it works

• A value exactly on a point is not past it, so nothing changes there.
• Equal points act as a simple comparator with no hysteresis, in the fill / heat
  direction: on below the point, off above it (documented, not an error).
• OnDelay / OffDelay: the value must stay past the point the whole time; a blip
  back starts the delay again.
• MinOn: once on, Q stays on at least this long. MinOff: once off, Q stays
  off at least this long. MinOff is not applied at start-up.
• The points are re-evaluated every scan, so changing or swapping them while
  running takes effect cleanly (through the delays).
• Enable FALSE turns Q off at once, even inside MinOn. MinOff counts from
  that moment.
• A NaN or infinite In, OnPoint or OffPoint holds Q as it is and sets
  BadInput; the delays start again once the value is good. Enable still
  turns Q off. Use BadInput to decide what the plant should do.
• Remaining is the longer of the delay and the minimum time still to run, so
  an HMI can show "starts in 1 m 20 s" (UT_TIME_TEXT).
  Waiting says the minimum time is the only thing holding Q ("Waiting:
  minimum off time").

Using it

SumpCtl(In := SumpLevel, OnPoint := 70.0, OffPoint := 25.0, OnDelay := T#5s, MinOff := T#2m);
SumpPumpAuto := SumpCtl.Q;    (* empty: on above 70 %, off below 25 % *)