MotionDetector

MotionDetector remembers a reference value and raises a flag when the signal drifts further than a threshold from it, in either direction. The flag stays raised until you reset it.

Use it to notice that something which should be standing still has moved — a brake slipping, a load settling, a clamped part creeping.

flowchart LR
    i1(["input"]) --> B["MotionDetector"]
    i2(["activate"]) --> B
    i3(["reset"]) --> B
    i4(["disable"]) --> B
    p1(["threshold"]) --> B
    p2(["enable"]) --> B
    B --> o1(["isTriggered"])
    B --> o2(["isEnabled"])
    B --> o3(["reference"])

Pulse reset whenever you raise activate. Raising activate on its own does not capture a new reference — the detector keeps comparing against whatever reference already holds, which is 0 after a controller start. reset is what captures the current input as the reference. Always send both.

Read reference to see what it is actually comparing against. It is published for exactly this reason, and it is the fastest way to tell whether the reference was captured when you expected.

There is no noise filtering. A single sample past the threshold latches the flag permanently. If your signal is noisy, filter it before this block or use WindowDetector, which has a time window.

Signals

Inputs

Outputs

Parameters

Both are persistent and survive a controller restart. No parameters exist below this block.

Setup

1. Connect the signal you want to watch to input.
2. Set threshold to how much movement you are willing to accept. It defaults to 0, which triggers on anything.
3. Bring the machine to the state you want to monitor and hold it there.
4. Raise activate and pulse reset in the same write.
5. Read reference and confirm it matches the current input. If it reads 0, the reset did not land — send it again.
6. Confirm isTriggered is false and stays false while the machine is still.
7. Nudge the machine past the threshold and confirm isTriggered latches.

This block only watches a signal and raises a flag. It does not move anything and cannot be made to — but whatever acts on isTriggered downstream will act the moment it latches.

Tuning

1. Trace input while the machine is in the state you want to monitor, for as long as you would normally leave it there.
2. Note the total spread — both the noise and any slow settling that is acceptable.
3. Set threshold above that spread, with margin. Too tight and you get false trips from noise; too loose and real movement goes unnoticed.
4. Re-arm and leave it for a realistic dwell. Confirm it does not trip.
5. If it trips on noise, either widen threshold or filter input upstream. Filtering is usually the better answer — a wide threshold hides real movement, whereas a filter only delays detection.
6. If you need to ignore short spikes rather than steady noise, WindowDetector with a timeWindow is the better block, at the cost of fixed levels instead of a captured reference.
7. Nothing here depends on the task rate, so none of this needs re-checking after a rate change.

The flag never falls once raised. That is what makes it useful between polls.

A starting point for an axis in metres that should not move:

threshold = 0.002
enable    = true

Limits and errors

This block logs nothing, ever. Every condition above shows as a value on a trace, or not at all.

Verified against motorcortex-control3 3.30.0 (bc348fd).