A sag sensor can trigger air support or the forming sequence at the wrong sheet position. Optical sensors are affected by dirt, reflections, transparent sheet, masking, color, ambient light, and frame movement. Mechanical or ultrasonic systems have their own alignment and response limitations.
The actual sheet position should be observed while the sensor signal and controller threshold are recorded. Calibration must be checked across the materials and finishes used in production. A sensor that works on opaque ABS may not detect clear sheet reliably without a different method or target.
Optics, brackets, wiring, thresholds, and the control sequence should be maintained as one system. Sag control should fail safely and should not conceal unstable heating. The validated recipe should include the intended sag geometry, not only the sensor setpoint.