Mayser SG-EFS — Safety Edge Fault LED & Cable Break

Mayser · intermediate · 20 min

A Mayser SG-EFS control unit turns its OSSDs off and lights the red Fault LED when it detects a problem with a pressure-sensitive safety edge — most often a cable break. Learn to read the Sensor/Output/Fault LEDs, check the 8k2 resistor wiring, and recover.

ℹ️ A Mayser SG-EFS evaluates a pressure-sensitive safety edge/bumper and switches its OSSD outputs. On a cable break the OSSDs go OFF, the red Fault LED lights, and the green Sensor and Output LEDs go out — that pattern is a broken/mis-wired sensor loop.

What the SG-EFS does

A Mayser SG-EFS control unit (e.g. SG-EFS 104/2W, 104/4L, 1X4 ZK2/1) processes the signal from a pressure-sensitive protective device (PSPD) — a safety edge, bumper or mat. It evaluates a sensor terminated with a monitoring resistor (typically 1k2 or 8k2) and switches the evaluated safety signal to the machine control through its integrated OSSD outputs. The electronics are single-fault-safe, dual-channel (redundant): each channel drives a force-guided relay (OSSD 1 and OSSD 2) and the two monitor each other.

Read the LEDs

The front LEDs tell you the state directly. The key fault pattern:

• On a cable break at the sensor: OSSD 1 and 2 go to the OFF state, the red "Fault" LED lights up, and the green "Sensor" and "Output" LEDs go out.

That combination — red Fault on, Sensor/Output off, outputs OFF — is the SG-EFS telling you the monitored sensor loop is open or out of range (a broken edge, a disconnected lead, or the wrong/missing terminating resistor).

Check the sensor and its monitoring resistor

Because the unit works by measuring the sensor's resistance, the wiring of the sensor and its monitoring resistor is where you look:

• Confirm the sensor with the 8k2 monitoring resistor is connected to the correct terminals — for the SG-EFS this is Y1 and Y3.
• If a cable break is detected, replace the sensor (or repair the broken conductor / restore the terminating resistor). A pressure-sensitive edge that's been crushed or flexed to failure will read as a break.

Step-by-step

1. Red Fault LED on, Sensor/Output off, OSSDs off? Treat it as a sensor-loop fault (most often a cable break).
2. Check the terminations — the 8k2 sensor connected to Y1 / Y3, correct monitoring resistor value (1k2 or 8k2 as specified).
3. Inspect the safety edge/cable for a break, crush, or disconnected lead.
4. Replace the sensor (or repair the conductor / resistor) if a break is confirmed.
5. Confirm recovery — Fault LED off, Sensor/Output green, OSSDs on — then re-validate the protective function.

Never do this

Never fit a plain resistor across the input to "satisfy" the SG-EFS and clear a Fault while the real safety edge is disconnected or broken — that defeats the pressure-sensitive protection entirely. Repair or replace the actual sensor, restore the correct monitoring resistor, and re-validate the safety function.