APM
All alarm codes
ALARM 156

Illegal Measuring Sensor Signal

Tool eye touch-off failed because the operator was not in jog mode (machine was in rapid or fast jog) when approaching the tool eye, or the approach distance...

Controls
Matrix
Machine series
Quick Turn Nexus

Causes

  1. Tool eye touch-off failed because the operator was not in jog mode (machine was in rapid or fast jog) when approaching the tool eye, or the approach distance was too large so the proxy timing did not match.

    • countryboy1966forum
      Not sure what I did differently, but the alarm went away and I'm on my way for the time being. I think its from trying a different approach distance.

How to clear it

  1. 1

    Bring the tool to about 1mm above the sensor before pressing Tool Measure, then feed in slowly with the axis jog button until the eye beeps.

    • Panzaforum
      I usually manually move the tool to about 1mm from the sensor, and then press "Tool measure" and move in until it beeps with the X or Y button.
  2. 2

    Before doing a tool set, jog the tool in the OPPOSITE direction a short distance first — that proves you are in JOG mode (not rapid) before approaching the sensor. Many tool eyes have been ripped off the machine by an operator in the wrong mode.

    • ToolCat (cnctoolcat)forum
      A good trick to learn is when jogging to set a tool, always move the tool the 'opposite' direction for a short distance, to make sure the machine is in JOG mode. Once you see the tool moving slow as it should, then you r…

Confidence: medium · Single thread, but the technique-based fix is from a senior PM member (ToolCat/cnctoolcat) and the OP confirmed it cleared.

First sourced: 5/21/2026