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

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

In the safety control circuit of industrial machinery and equipment, emergency stop monitoring and protective door interlocking are the most basic and important functions. The SNO 4062K and SNO 4062KM series safety relay modules are designed for single or dual channel emergency stop monitoring in accordance with DIN EN 60204-1 and EN ISO 13849-1, with a maximum capacity of PL e, Class 4, and SILCL 3 (according to DIN EN 62061). This series of products is widely used in fields such as stamping machinery, automated production lines, robot workstations, and packaging equipment. However, due to on-site electromagnetic interference, wiring errors, contact wear, or external sensor failures, these safety relays may experience typical issues such as inability to start, non functioning output contacts, and flashing LED alarms. This article is based on official technical information and combined with actual maintenance experience to systematically sort out the selection points, typical fault diagnosis, and standardized troubleshooting methods of SNO 4062K/KM, helping on-site engineers quickly restore equipment safety functions.

Product Series Overview and Model Differences

SNO 4062K and SNO 4062KM are both basic safety switch units with built-in forced pilot relays and self-monitoring for each ON-OFF cycle. Both provide two enable contacts (13-14, 23-24) and one signal contact (31-32), supporting manual or automatic start, optional with/without cross short circuit detection, and feedback loop with external contactor monitoring (S33-S34). The core differences between the two are as follows:

Characteristics SNO 4062K SNO 4062KM

Synchronous monitoring supports dual channel synchronous time monitoring (tS), requiring CH1 to close before CH2 without synchronous monitoring function

Suitable for input devices such as emergency stop buttons, safety door switches, and light curtain OSSD outputs. In addition to the above, it is also suitable for safety carpets (4-wire system, no monitoring resistors)

Input debouncing is absent to prevent frequent switching of output relays due to rapid on-off of input signals

Typical applications include emergency stop, safety doors, light curtains, safety carpets, and frequent manual operations (such as manual feeding)

Ordering information:

Model Rated Voltage Wiring Method Order Number

SNO 4062K AC/DC 24V 50-60Hz cage spring terminal R1.188.0699.2

SNO 4062K-A AC/DC 24V 50-60Hz pluggable connector R1.188.0709.2

SNO 4062KM AC/DC 24V 50-60Hz cage spring terminal R1.188.0719.2

SNO 4062KM-A AC/DC 24V 50-60Hz pluggable connector R1.188.0729.2

Selection suggestion: If you need to monitor safety carpets or have frequent and rapid on-off conditions (such as jog operation during manual feeding), you should choose SNO 4062KM to utilize its input anti shake function. If the device requires time monitoring due to synchronization requirements (such as protective doors must be opened and closed in a specific order), SNO 4062K should be selected.

Detailed explanation of core functions and working modes

2.1 Basic working principle

After power on, supply power to the module through terminals A1/A2. When both safety input channels (CH1, CH2) are closed, the internal forced pilot relay is activated through a reset input (manual or automatic start) to enable the output contacts to close. When any safety input is disconnected, the enable contact immediately disconnects, cutting off the power source in the hazardous area.

2.2 Operating Mode Settings

According to on-site requirements, the following modes can be configured through external wiring:

Explanation of Mode Wiring Method

Single channel control with parallel connection of two safety channels (S12 and S31 short circuited to S11) is not recommended for high safety levels

Dual channel non crossing detection S12 and S31 are connected to high level (+24V), and S11 is connected to the common terminal without line short circuit monitoring

Dual channel with cross detection CH1 connected to positive potential (S11-S12) and CH2 connected to negative potential (S21-S22) can detect short circuits between the two channels

Manual start (with reset button monitoring), connect to the reset button (triggered by the falling edge) in S3; Press the button to connect the bridge from S35 to S33 or suspend it for each startup

Automatically start the short circuit between S35 and S33, and the unit does not require manual reset to start on the rising edge when the safety input is closed

Even if the safety input is closed, the startup lock will not start after power on. The reset button must be pressed to prevent automatic operation when powered on

After the safety input is disconnected and then closed, it will not automatically restart. The reset button needs to be pressed to meet higher safety standards

2.3 Synchronization Monitoring of SNO 4062K

When dual channel control is enabled and synchronous monitoring is enabled, it is required that the safety channel CH1 must be closed before CH2, and the time difference between the two closures cannot exceed the synchronization time tS. If CH2 closes before CH1, synchronous monitoring will be triggered, and the enable circuit cannot be closed. Common on-site problem: Connecting the two sets of contacts of the emergency stop button in reverse order during wiring, resulting in the module being unable to start. The solution is to check the switching sequence of the two channels or disable synchronous monitoring by short circuiting S33/S35 (see wiring diagram for details).

2.4 SNO 4062KM input stabilization

For applications where safety carpets or mechanical contacts are prone to bounce, the input anti shake function can prevent output relay misoperation caused by brief disconnection (less than tASP). The output will only disconnect after tR if the safe input disconnect time is longer than tASP; After re closing, it still needs to go through tSP before it can be restarted. This is particularly important in situations where quick switch operations such as manual feeding can significantly reduce the mechanical wear of relays.

Wiring specifications and common errors

3.1 Power Supply and Protection

Power supply: Terminal A1/A2, AC/DC 24V, 50-60Hz.

External protection: A maximum 6A gG fuse or B/C characteristic circuit breaker must be used. The module is equipped with built-in short-circuit protection, which automatically recovers within about 3 seconds after the fault is removed.

Attention: The control output S11 is only used to connect control devices defined in this manual (such as emergency stop buttons, safety door switches, etc.), and should not be connected to external loads such as lamps, relays, or contactors.

3.2 Cross Short Detection

When enabling cross detection, wiring requirements:

CH1 (S11-S12) provides+24V signal

CH2 (S21-S22) provides 0V signal

When a short circuit occurs between two channels, the voltage is pulled low or high, and the module will detect and immediately cut off the enable output, while the electronic fuse is triggered. Common mistake on site: Connecting both channels to+24V resulted in failed cross detection. Be sure to connect according to the manual.

3.3 Feedback Circuit

Terminals S33-S34 are used to monitor the auxiliary contacts of external contactors (such as K1, K2). At startup, the module will check if the feedback loop is closed. If the external contactor is not engaged or the auxiliary contacts are not properly connected, the module will not be able to start. This is a key safety measure to prevent contactor adhesion.

Common wiring errors:

Forgot to short-circuit S33-S35 or S33-S34 (depending on startup mode).

Connected the feedback contact to other signals.

Typical application cases and parameter settings

4.1 Dual channel sliding safety door (with cross monitoring, manual start)

Wiring diagram (see top of page 4 of the PDF):

The two contacts of the safety door are respectively connected to S12 (CH1) and S22 (CH2).

Enable cross detection: S11 connected to+24V, S21 connected to 0V.

Manual start: Reset button connected to S34, S33 connected to+24V, S35 suspended or bridged to S33 (depending on specific configuration).

workflow

After power on, the safety door closes and both channels are closed.

Press the reset button (triggered by the falling edge), the module will engage, enabling contacts 13-14 and 23-24 to close, and signal contacts 31-32 to open.

The safety door opens, any channel is disconnected, and the output is immediately disconnected.

After the safety door is closed again, the reset button must be pressed again to restart.

Troubleshooting: If unable to start, check if the closing sequence of the two contacts of the safety door meets the synchronous monitoring requirements (if enabled); Measure the voltage between S12 and S11 (should be+24V), and between S22 and S21 (should be 0V). If the voltage is correct but there is no output, check if feedback loops S33-S34 are closed.

4.2 Dual channel safety carpet (with cross monitoring, manual start and reset button monitoring)

Suitable for SNO 4062KM, wiring can be found in the middle of page 4 of the PDF.

The safety carpet is a 4-wire system, with two outputs connected to CH1 (S11-S12) and CH2 (S21-S22) respectively.

Effective cross detection: When no one steps on the carpet, a short circuit path is formed, and both channels are conductive; When someone steps on the carpet, the internal structure of the carpet causes both channels to disconnect or short-circuit simultaneously.

The reset button is connected to S3 (triggered by the falling edge).

Working characteristics: Only when the safety carpet is not stepped on, it is allowed to start through the reset button. Once someone steps on the carpet, the output is immediately cut off.

Common faults:

The module cannot start when the carpet is not stepped on → Check if the carpet output resistance is<50 Ω/channel. If the resistance is too high, replace the carpet.

After stepping on the carpet, the output keeps on → Check if cross detection is enabled and if S21 is connected to 0V.

4.3 Dual channel emergency stop application (with cross monitoring, manual start)

Wiring can be found at the bottom of page 4 of the PDF.

The emergency stop button has two normally closed contacts connected to S12 and S22 respectively.

Enable cross detection, connect S11 to+24V and S21 to 0V.

Manual start, with reset button monitoring.

Safety feature: If one of the contacts is stuck (such as S12 side cannot be disconnected), when the emergency stop is pressed, the other contact S22 will still disconnect. The module recognizes that the two channel states are inconsistent (one remains high and the other becomes low), triggering the safety output to disconnect. Meanwhile, cross detection can also detect short circuits between two channels.

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)

Supporting pluggable terminal blocks (for - A model)

External contactors (such as Schneider TeSys D series with forced guiding contacts)

Industrial grade fuse (6A gG)

Common error codes and LED indications

This module provides diagnostic information through the combination flashing of SUPLY and CH1/CH2 LEDs:

LED status meaning processing

SUPLY is always on, the power supply is normal, the safety input is closed, and the output may have been pulled in normally

Check for a short circuit between S12-S22 when there is a fast flashing (about 2Hz) cross short circuit or short circuit at the output terminal of SUPLY; Check external load

SUPLY slow flashing (approximately 0.5Hz) safety input asynchronous (only SNO 4062K) adjust switch sequence or disable synchronous monitoring

CH1 LED not on, CH1 circuit disconnected, measure conductivity between S11-S12

CH2 LED not lit, CH2 circuit disconnected, measure conductivity between S21-S22

All LED power failure checks A1-A2 voltage