HighPass1

HighPass1 removes the slow content of a signal and keeps the fast — sensor drift, a thermal offset, a load cell’s zero error.

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3.30–3.34

HighPass1 removes the slow content of a signal and keeps the fast — sensor drift, a thermal offset, a load cell’s zero error. One cut-off frequency governs every channel, and the channel count is fixed by the machine configuration. Its steady output for a constant input is zero, not the input: this block deletes the part of the signal that does not change.

flowchart LR
    i1(["input — signal to wash out"]) --> B["HighPass1"]
    i2(["disable"]) --> B
    B --> o1(["output — fast content of the input"])
    B --> o2(["isEnabled"])

$f_c = \omega/2\pi$ — omega 6.283 rad/s is a 1 Hz cut-off. Time constant $\tau = 1/\omega$ [s]: a step appears in full, then decays to 37% in $\tau$ and to 1% in $4.6,\tau$. At the cut-off: gain 0.71 and 45° of phase lead. Signals slower than the cut-off are removed; signals faster pass at gain 1. Choosing omega is choosing how slow “slow” means.

This block has no derivative output and no reset input. It also cannot be bypassed without restoring the offset it was removing — see the symptom table.

Signals

Inputs

Path Unit Range Description
input signal unit unbounded The signal to wash out. One element per channel; the channel count is fixed by the machine configuration.
disable - - True bypasses the filter: input passes straight to output, offset included. Use it for a runtime override from a supervisor; use enable for the configured intent.

Outputs

Path Unit Description
output signal unit The fast content of input, one element per channel. Settles to zero for any constant input. Equals input exactly while bypassed. Starts from the full value of input after every controller start, then washes out over $\tau$.
isEnabled - True when enable is true and disable is false. A single value for the whole block, not one per channel.

Parameters

Path Unit Default Range Effect
omega rad/s 6.283 (1 Hz) 0.1 – 0.628/task period [s] Cut-off, shared by all channels. Lower keeps more of the slow content and takes longer to wash a step out. Higher removes more, and starts eating the signal you wanted to keep. Out-of-range values are corrected silently — see Limits and errors.
enable - true - False bypasses the filter: input passes through unchanged, offset included.

Both parameters are persistent and survive a controller restart. The inputs and outputs do not. No parameters exist below this block.

Setup

  1. Link the source signal: …/sensor/rawForce → …/forceWashout/input. input follows the source on a trace.

  2. Set enable false. output equals input sample for sample and isEnabled reads false.

  3. Set omega to 300. Read it back; a lower value means your task rate capped it, and tells you the highest cut-off this task rate allows.

  4. Hold the machine still and note the constant value input sits at. That offset is what the block is going to remove.

  5. Set enable true. output starts at the full value of input, then decays toward zero. Time that decay — it reaches 37% of the way at $\tau$.

    Step 5 injects the whole offset into whatever consumes output. The filter starts from a clean state, so its first sample is the input in full. Enable it with the machine at rest and the consumer gated off.

  6. Hold the machine still again. output should sit at zero, not at the offset from step 4. If it does not, the cut-off is too low for the drift you have.

  7. Trace every element of input and output. An element that reads zero while the machine moves is an unwired channel, not a washed-out one.

Tuning

  1. Decide the slowest signal you want to keep, in Hz. Set omega to $2\pi$ times that frequency; everything slower than it will be removed.
  2. Measure the drift you want gone. Read how long the offset takes to build on a trace, in seconds; omega must be at least a few times $1/$that.
  3. Check the two against each other. If the drift builds as fast as the signal you want to keep, no cut-off separates them and this block cannot help.
  4. Step the machine and read the decay off output. The time to 37% is $\tau$, and $\tau$ is how long a genuine step survives before the filter eats it.
  5. Confirm the steady state with the machine at rest: output at zero, not at an offset.
  6. Re-check omega after any task-rate change. The upper bound scales with the task period, so a slower task can clamp a cut-off that used to be accepted.

Response to a step at three cut-offs: omega 20 washes the step out within0.2 s, omega 6.283 decays to 0.37 at 0.16 s, and omega 2 still holds 0.14 ofthe step after a second.

Read the time constant off any curve as the moment it crosses 0.37.

Symptom Cause Action
output sits at zero while input clearly has a value Expected: a constant input has no fast content, so there is nothing to pass Confirm with a moving signal; if that also reads zero, the channel is unwired
The offset is still on output at rest Cut-off too low for the drift Raise omega; if the drift is as fast as your signal, this block cannot separate them
A genuine slow movement got deleted Cut-off too high — the block cannot tell drift from slow signal Lower omega, and accept that some drift stays
output jumps to the full input value the moment the filter is enabled Expected: the block starts from a clean state, so the offset appears once and washes out over $\tau$ Enable at rest, or gate the consumer off isEnabled plus a few $\tau$
The same jump every time disable is toggled off Expected: the same reason — the state is cleared while bypassed Do not toggle the bypass during operation; leave enable set and use it as configuration
Bypassing the filter put a large offset back on output Expected: bypass restores the input in full, including the DC the filter was removing Bypass only when the consumer can accept the raw signal
output overshoots the other way after a step Expected: the block removes the step’s steady part, so the output must return through zero None; this is what a washout does
omega reads back lower than written Outside the accepted band for this task rate Raise the task rate or accept the cap
omega reads back as 0.1 Written below the fixed lower bound Write 0.1 or more; a slower washout is not available
omega used to be accepted and now clamps The task period grew, so the upper bound fell Raise the task rate back, or lower omega
You need the rate of the washed-out signal The block publishes no derivative Differentiate downstream, or filter first and difference after
Some channels wash out faster than others Not possible — all channels share one omega Use a separate filter per channel group
output went to a non-numeric value and stays there A non-numeric value reached input or omega Fix the source, then bypass the filter for one cycle — that clears its state

A conservative starting point for washing thermal drift off a force signal on a 1 ms task, keeping everything above about 0.5 Hz:

omega  = 3.14
enable = true

This is a starting point, not a final tuning. Work steps 1 to 3 with a trace of your own signal.

Limits and errors

Limit Set by What happens Reported
omega ≥ 0.1 rad/s Fixed A slower value is replaced by 0.1 rad/s Silently; read omega back
omega ≤ 0.628 / task period [s] Task rate — 628 rad/s on a 1 ms task, 62.8 rad/s on a 10 ms task A faster value is replaced by the edge. This is what keeps the filter stable at any setting Silently; read omega back
output Nothing Unbounded — a fast input reaches the output at full size. Limit it downstream if the consumer needs a bound Not reported
Channel count Machine configuration Fixed once the controller starts; it cannot be changed at runtime Not reported

The block raises no errors or warnings and logs nothing. Every failure above shows as a value on a trace, not as a message.

Verified against motorcortex-control3 3.30.0 (bc348fd).