Keyence GS interlock switch

In modern industrial automation production lines, monitoring the switch status of safety doors, protective covers, and maintenance windows is the core link to ensure personnel safety and equipment compliance operation. The GS Series safety interlock switch launched by Keyence quickly became a benchmark product in the field of mechanical safety due to its compact size, sturdy structure, and diverse installation methods. This series is divided into Locking Type and Non Contact Type, respectively suitable for high inertia equipment and light load protection scenarios.

However, any safety device will face problems such as wiring aging, mechanical wear, and parameter configuration errors during long-term operation. Engineers often need to quickly obtain technical details and troubleshooting ideas when selecting, installing, or maintaining GS Series. This article is based on the official technical information of GS Series and combined with common on-site situations. It systematically summarizes the selection points, wiring cascade scheme, typical fault diagnosis and replacement steps of this series of safety interlock switches, aiming to provide a practical "handy guide" for automation maintenance personnel.

Chapter 1 Product Positioning and Comparison of Two Major Types

1.1 Locking Type

The locking type safety interlock switch is suitable for equipment that may maintain hazardous energy even after the machine has stopped, such as large flywheels, inertia operated stamping machines, fans, etc. The GS Series locking type has the following core features:

Holding force of 2000 N: Even if the operator forcibly pulls the protective door, it cannot open the locked state, ensuring that the dangerous area cannot be entered.

Power off hold or release optional: Depending on the model, users can choose to keep locked after power off (applicable to high inertia devices) or automatically unlock after power off (applicable to low inertia devices).

Manual release device: In emergency situations or maintenance, it can be unlocked from the outside using a specialized tool.

Lock/Tag Out (LOTO) Design: Metal head with reserved lock holes for easy execution of energy isolation procedures.

1.2 Non Contact Type

Non contact type is suitable for detecting the position of doors, covers, or moving parts that do not require mechanical locking. Its characteristics include:

Wide switch range (ON-OFF distance ≤ 18 mm): Even if the door body undergoes slight deformation or vibration, it can stably output safety signals to avoid frequent false shutdowns.

Metal casing: resistant to mechanical impact and dust environment, with a longer lifespan.

High visibility indicator light: Quickly identify the opening and closing status of the door through large-sized LED.

1.3 Selection Decision Matrix

Application scenario recommendation type key parameters

Inertial shutdown time>5 seconds lock set (power-off holding) 2000N holding force, manual release

Immediately after a power outage, the non hazardous locking type (power off unlocking) requires a power on locking signal

Light load door, sliding door, vibration environment non-contact 18mm switch distance, metal shell

Non contact type for confirming the origin of moving parts as a position sensor

Chapter 2 Core Functions and Design Highlights

2.1 Compact and sturdy balance

The GS Series locking type is only half the size of traditional safety switches and can be installed in aluminum frame or narrow spaces. The non-contact type adopts a mixed structure of all metal head and plastic body, which not only reduces weight but also ensures impact resistance. Both models achieve IP65/IP67/IP69K protection levels and comply with NEMA 3, 4X, 12, and 13 standards, making them suitable for direct use in high-pressure water washing or oily environments.

2.2 High visibility status indicator light

The indicator light adopts a large-sized chamfered design with adjustable brightness (configured through M12 wiring), which can be clearly distinguished from multiple angles. Green constant light indicates that the door is closed and the safety output is ON; red flashing indicates a fault or insufficient locking. This design significantly improves inspection efficiency.

2.3 Built in cascading function

In traditional safety circuits, if multiple safety doors are connected in series, each switch usually needs to occupy an independent safety relay input or use a complex junction box. Each unit of GS Series has OSSD output direct function:

Connect the OSSD output of the first switch to the OSSD input of the next switch, and so on.

The OSSD output of the last switch is connected to a safety relay or PLC safety module.

Up to 32 units can be cascaded while still maintaining the PL d/e level.

After cascading, the status of all switches is transmitted only through a pair of safety signal lines, greatly simplifying the safety wiring of multiple devices.

2.4 Built in auxiliary output and reset function

Each GS Series switch (especially the M12 connector model) provides additional AUX output (PNP/NPN). This output can be connected to a regular PLC input or indicator light to individually locate which door is opened without interfering with the safety circuit. At the same time, some models integrate EDM (External Device Monitoring) and manual reset functions, which can be directly connected to the contactor feedback loop without the need to purchase additional safety relays.

2.5 E-Stop direct series connection

Some GS models have safety input terminals that allow the emergency stop button to be directly connected in series with the safety circuit, eliminating the need for a separate emergency stop module. For example, the emergency stop normally closed contact is connected to the Safety Input of the switch. When the emergency stop is pressed, the OSSD output of the switch is synchronously cut off.

2.6 Flexible Encoding and Anti tampering

Low encoding mode: Any GS series actuator can be triggered, suitable for quick replacement.

High encoding mode: The switch locks the unique actuator through a learning mode to prevent unauthorized keys or foreign objects from forcibly triggering on-site personnel.

Chapter 3 Selection and Accessories Guide

3.1 Model Naming Rules

The GS Series is encoded according to the following rules: GS-5x (non-contact type) or GS-7x (locked type), and further subdivided based on cable type and output logic.

Basic Model Type Output Logic Cable Form

GS-51P5 non-contact PNP 5-meter standard cable

GS-51N10 non-contact NPN 10 meter standard cable

GS-71PC Locking PNP M12 Connector (8-Pin)

GS-73PC Locking PNP M12 Connector (12 Pin)

M12 connector type requires additional ordering of cables (such as GS-P5C5, GS-P8C5, GS-P12C5), with different pin numbers corresponding to different functions: 5-pin only provides OSSD and power supply; 8 needles increase AUX and EDM; 12 pin supports complete cascading and reset functions.

3.2 Special installation bracket

To meet the on-site installation needs that are tailored to local conditions, Keyence offers a variety of brackets:

GS-B01: Universal L-shaped bracket

GS-B11: Flat bracket for sliding doors (left/right optional)

GS-B41/GS-B43: Special bracket for hinged doors, supporting outward or inward opening of the door body

GS-H01/GS-H02: Locking type dual action handle (requires pressing and sliding to unlock)

The brackets are equipped with mounting screws, made of galvanized steel or stainless steel, and can be directly welded or bolted in place.

3.3 Cable and Y-shaped splitter

For scenarios with double doors or the need to monitor two entrances simultaneously, it is recommended to use a Y-shaped connector (such as GS-Y5P). This connector divides a safety signal source into two paths, which are respectively connected to the left and right door switches, and each switch can still output an independent AUX signal, making it easy for the upper computer to identify the specific door opening position. The Y-shaped connector, when paired with standard M12 extension cables (1m, 5m, 10m, 20m), can easily build a distributed secure network.

Chapter 4: Practical Installation and Wiring

This chapter provides a detailed description of the installation steps using the most common locking type (M12 8-pin) and non-contact type (5-meter cable) as examples.

4.1 Key points of mechanical installation

Determine installation position: For the locking type, the actuator (key) must be inserted vertically into the switch slot, with an insertion depth of ≥ 15mm and an inclination angle of ≤ 5 °. The non-contact type allows for a larger tilt angle (± 15 °) while keeping the head parallel to the actuator.

Use a dedicated bracket for fixation: First, fix the bracket to the machine frame with screws, and then install the switch body. The elongated holes on the bracket can be adjusted in position to compensate for welding or assembly errors.

Door side actuator adjustment: After installing the actuator on the door, slowly close the door and check if the actuator can smoothly enter the switch head. If stuck or rubbed, perform three-axis alignment through shims or long holes.

Connecting the grounding wire: The metal casing must be connected to the system grounding through a bracket or an independent grounding wire to prevent static electricity accumulation and misoperation.

4.2 Electrical Wiring - Non Contact Type (Cable Direct Output)

Non contact type is usually equipped with 5m or 10m standard cables, containing 4 wires inside:

Brown:+24V DC

Blue: 0V

Black: OSSD output 1

White: OSSD output 2 (redundant safety output)

(Optional gray: AUX output)

Wiring steps:

Connect the brown color to the safety power supply+24V and the blue color to 0V.

Black and white are respectively connected to the two safety input channels of the safety relay (such as S11 and S21).

If using AUX output, connect the gray line to the PLC digital input module (PNP type source input, NPN type drain input).

Check that the OSSD output remains high (+24V) when the door is closed and drops to 0V when the door is open.

4.3 Electrical Wiring - Locking M12 Connector

Taking the 8-pin model (GS-71PC) as an example, using GS-P8C5 standard cable, the wire color is defined as follows (refer to Keyence definition):

Explanation of Needle Number Line Color Signal

1 brown+24V power supply positive

2 white safety inputs 1 from the previous level OSSD or reset button

3 blue 0V power supply negative

4 Black OSSD Output 1 Safe Output Channel A

5 gray OSSD outputs 2 safe output channels B

6 Pink Lock Control High Level (24V)=Lock, Low Level=Unlock

7 yellow EDM feedback input connected to contactor auxiliary contact

8 green AUX output status monitoring

Cascade wiring example (two locked switches in series):

The OSSD1/2 (black, gray) of the first switch is connected to the safety input 1/2 (white, certain pin) of the second switch.

The OSSD1/2 of the second switch is connected to the safety relay.

Locking the control line (powder) requires simultaneous control of all switches (in parallel), otherwise partial locking and partial unlocking may occur.

It is recommended to use star connection for both 0V (blue) and+24V (brown) of all switches to avoid voltage drop.

4.4 Integrated emergency stop button

Connect the normally closed contact of the emergency stop button in series with the front end of the safety input of the first switch. Attention: The emergency stop contact must comply with the mandatory disconnection structure required by ISO 13849.

Chapter 5 Common Malfunctions and Troubleshooting Methods

5.1 Fault phenomenon: After the door is closed, the indicator light remains red and the safety output is not turned on

Possible reasons:

The actuator has not fully entered the switch slot (such as door sagging).

The encoding mode is set to HIGH, but the actuator is not learned.

The non-contact distance exceeds 18mm or the lateral offset is too large.

Exclusion steps:

Manually press down the door and observe if the indicator light turns green. If it remains unchanged, loosen the actuator fixing screw and fine tune the position.

Enter High encoding learning mode: Power on the switch, insert the actuator to be learned into the slot (or near the sensing surface), and hold for 5 seconds before the switch automatically memorizes.

For non-contact types, measure the gap with a feeler gauge to ensure it is ≤ 18mm.

5.2 Fault phenomenon: The locking type cannot be locked/unlocked, or there is high mechanical resistance when locking

Possible reasons:

The voltage of the lock control signal (pink line) is insufficient (<19V).

Mechanical jamming: foreign objects or deformations in the actuator or switch head.

Internal wear and tear of the locking mechanism (often occurring in doors that are frequently opened and closed).

Exclusion steps:

Measure the voltage of the pink wire to 0V, which should be within the range of 24V ± 10%. If it is too low, check the power cord diameter and voltage drop.

Disconnect the power and use a manual release tool (Allen wrench) to try turning the lock tongue and feel if it is stuck. If it is stuck, the switch needs to be replaced.

Check for burrs or dents on the surface of the actuator and replace it if necessary.

5.3 Fault phenomenon: After a certain switch in the cascade system is turned on, the safety output of the entire system is not cut off

Possible reasons:

The OSSD output of this switch has an internal short circuit failure.

In the cascading connection, the OSSD output was mistakenly connected to the input of the same switch (self loop).

Exclusion steps:

Disconnect the cascade circuit and test each switch separately: directly supply power to the switch, manually trigger the actuator, and measure whether the OSSD output switches normally.

If the OSSD remains high when a certain switch is turned on, it is determined that the switch has an internal fault and needs to be replaced.

Confirm the cascading sequence: OSSD output of the first switch → safety input of the second switch → OSSD output of the second switch → third... Do not cross.

5.4 Fault phenomenon: AUX output status is inconsistent with OSSD

Possible reasons:

AUX output configuration is set to "diagnostic" mode instead of "door status" mode (some models can be set through software).

Wiring error: AUX negative output.

Exclusion steps:

Refer to the manual to confirm the default logic of AUX: usually AUX is opposite to OSSD (AUX=ON when the door is open, AUX=OFF when the door is closed).

Measure the voltage of AUX to 0V with a multimeter. The PNP type output should be 24V or 0V, and the NPN type should be checked for connectivity with COM.

5.5 Fault phenomenon: IP69K switch has water ingress inside after washing with water

Reason: M12 connector not tightened or cable sheath damaged.

Countermeasure:

During installation, the M12 nut must be turned to a "click" sound and it is recommended to wrap it with waterproof tape.

Check if the cable entrance is facing downwards to prevent water from entering the connector along the cable.

Chapter 6 Maintenance and Security Verification

6.1 Regular inspection items (once every quarter)

Locking force test: Use a force gauge to pull the locked door, and the maximum force should be greater than 1500N (2000N from the factory, allowed to decrease by 20% after wear).

Switch distance verification (non-contact type): Measure the gap with a feeler gauge and record it. If it exceeds 18mm, readjust the bracket.

Response time measurement: Use an oscilloscope to capture the time from the moment the door opens to the falling edge of OSSD, which should be less than 20ms.

Indicator light brightness: It should be clear and distinguishable under ambient light. If it becomes dim, consider replacing the internal LED (overall switch replacement).

6.2 Standard process for replacing faulty switches

When determining that a certain switch is damaged, follow the following steps:

Cut off the system power and lock the main circuit breaker (LOTO).

Remove the M12 connector of the faulty switch or cut the cable (leaving enough margin).

Record the model and coding settings (High/Low) of the old switch.

Install a new switch and re crimp or plug the wiring according to the original definition.

If the original system uses High encoding mode, perform a learning operation on the new switch (or re learn the entire system).

Power on test: Repeatedly open and close the door 10 times to confirm that the safety output logic is correct and there are no unexpected interruptions.

Fill in the maintenance record form, including replacement date, batch number, and test results.

6.3 Special Operations during Lock/Tag Out (LOTO) Period

For lock type switches, in addition to cutting off the main power supply, mechanical locking should also be performed during equipment maintenance:

Thread a specialized lock (such as a padlock) through the lock hole on the switch head to prevent the locking mechanism from retracting.

Even if accidentally powered on, the door cannot be opened, providing double protection for maintenance personnel.

Chapter 7 Compliance with Safety Standards

The GS Series series meets the following standards and can be easily integrated into PL e and SIL 3 level safety circuits:

ISO 13849-1：Category 4，PL e

IEC 61508：SIL 3

IEC 60947-5-3: Special requirements for non-contact position switches

UL 508/CSA C22.2: North American Certification

When using, users should ensure that the diagnostic coverage (DC) of external safety relays or PLC safety modules matches the switch. The built-in EDM function can monitor faults such as melting of external contactor contacts, further improving system reliability.