SNO 4062K/SNO 4062KM Safety Relay On site Troubleshooting and Selection Replacement Guide

On site issues:

Unable to reset after emergency stop → Check if the reset button itself is stuck (periodic self check before unsealing will detect a short circuit on the reset button).

Frequent module errors → Use a multimeter to measure the resistance between S12 and S11, S22 and S21, and confirm that the normal state is conductive (<1 Ω).

On site troubleshooting checklist

Possible causes and solutions for the fault phenomenon

After power on, the SUPLY LED does not light up. If the power supply is not connected or the voltage does not match the measured voltage between A1-A2, it should be 24V AC/DC

SuperpLY LED flashing cross short circuit detection triggered; Or if the output short circuit causes the electronic insurance to operate, check whether there is a short circuit in the safety input circuit (between S12 and S22); Disconnect the load and check if it has been restored

Safe input closed, no response when pressing reset button. 1. Synchronization monitoring timing error (CH2 closed first)

2. Feedback loop not closed

3. Reset button wiring error 1. Check the closing sequence of CH1 and CH2, or short circuit S33/S35 to turn off synchronous monitoring

2. Check if the auxiliary contacts of the external contactor are closed (S33-S34)

3. Confirm the reset button type (normally open) and wiring

After the safety door is closed, the automatic start (no reset required) module is configured to disconnect the connection between S35 and S33 in automatic start mode and switch to manual start

Measure the resistance of the safety input channel due to internal relay failure or poor contact of the safety input circuit when the output contact cannot be closed; If there is a backup circuit, try replacing the module

When using the light curtain OSSD output, the module cannot work. If the OSSD output type does not match or the test pulse width is too large, confirm that the light curtain output is PNP and compatible with the module; The test pulse width should be less than tTP, otherwise the module will lock

After stepping on the safety carpet, the output is not immediately disconnected and the input anti shake module is temporarily delayed (only SNO 4062KM). This is a normal phenomenon. If a faster response is needed, it may be considered to replace it with a non anti shake module

After the module is locked, it cannot recover from internal faults or external short circuits that have not been resolved. If the external fault is resolved, power on again. If still locked, replace the module

Precautions for Connecting with Light Curtain OSSD

SNO 4062K/KM compatible OSSD output for light curtains (semiconductor switching elements). However, it should be noted that:

The test pulse width output by the light curtain must be less than the tTP allowed by the module, otherwise the module will misjudge and interlock (stop output).

It is recommended to install interface relays between the light curtain and the module, or choose OSSD with "no test pulse" mode.

Specific wiring: Connect OSSD1 to S12 (CH1), OSSD2 to S22 (CH2), and the common terminal to S11 and S21 (positive/negative logic should be selected according to the polarity of the light curtain output). Please refer to the light curtain manual for details.

Expanding contact capacity and selecting external contactors

When switching to larger current loads (such as motor main contactors), the rated capacity of the two enable contacts (13-14, 23-24) of SNO 4062K/KM is limited (usually for 6A resistive loads). The external contactor must be driven by the output coil of the module, and then the power supply must be cut off by the main contact of the contactor. At the same time, connect the auxiliary normally open contacts of the external contactor to the feedback loop of the module (S33-S34) to achieve contact redundancy monitoring.

Selection suggestion:

External contactors should be of the forced guide contact type (compliant with EN 50205) to ensure fault detection.

Each contactor coil circuit needs to be connected in series with one enabling contact of the module to achieve redundant disconnection.

Preventive maintenance and spare parts recommendations

The lifespan of the safety relay module can reach hundreds of thousands of operations under normal working conditions, but the following situations may shorten its lifespan:

Frequent emergency stop/reset cycles (such as manual feeding equipment)

High environmental humidity and corrosive gases

External load short circuit causes internal relay contacts to burn out

Recommended maintenance plan:

Project cycle content

Visually inspect monthly for loose terminals, cracked casing, and normal LED status

Functional testing manually triggers safety inputs every quarter to confirm reliable disconnection of output contacts

Cross checking verification: Every year, artificially create short circuits between channels and observe whether the module cuts off the output and flashes the LED

It is recommended to replace it after 5 years or 1 million operations, even if the function is normal, to ensure the reliability of the contacts

Spare parts list:

SNO 4062K or SNO 4062KM module body (order according to the original model)