SICK RLY3-EMSS300 Safety Relay Manual

SICK RLY3-EMSS300 Safety Relay Configuration and Troubleshooting Guide

In the machine safety protection system, safety relays play a key role as evaluation units in connecting sensors and actuators to ensure reliable shutdown of hazardous states. The RLY3-EMSS300 launched by SICK is a compact (18mm width) safety relay designed specifically for safety sensors with passive contact outputs. It can reach up to SIL 3 (IEC 61508), Cat. 4, and PL e (ISO 13849-1), with a hazard failure rate PFHp as low as 1.0 × 10 ⁻⁹ per hour and a mission time of 20 years. This device has 3 forced guided safety output contacts, 2 diagnostic outputs, 3 test pulse outputs, and supports functions such as external device monitoring (EDM), reset interlock, differential monitoring, and cross circuit detection. This article will provide a detailed discussion on the technical parameters, safety features, wiring configuration, typical applications, and troubleshooting of RLY3-EMSS300, providing a practical guide for automation engineers to refer to directly.

Product Overview and Core Application Scenarios

RLY3-EMSS300 belongs to the SICK ReLy series of safety relays, designed to provide a high-performance evaluation platform for electromechanical safety switches such as safety door switches, emergency stop buttons, dual hand control boxes, safety touchpoints, etc. Unlike complex safety PLCs that require software parameterization, this device adopts a hard wired configuration, where all functions are implemented through terminal connections without programming, making it ideal for scenarios that require high debugging speed and on-site maintainability.

Typical applications include:

Monitoring of emergency stop button (single channel or dual channel)

Monitoring of protective door switches (with or without locking function)

Output evaluation of safety light curtains/gratings (via passive contacts)

Monitoring of safety carpets or safety edges

Evaluation of Two Hand Operated Control Boxes (Compliant with EN 574)

As a safety signal relay for higher-level control systems

This device complies with stop category 0 (IEC 60204-1), which means that the actuator power is immediately cut off without delay upon safety triggering.

Detailed technical specification interpretation

2.1 Safety parameters

Meaning of parameter values

SIL 3 is suitable for applications with the highest safety integrity level

Category 4 conforms to the highest structural category of ISO 13849-1

PL e performance level highest level

PFHp 1.0 × 10 ⁻⁹ has an extremely low hazard failure rate per hour and is suitable for high demand mode

TM has a 20-year mission duration, during which the safety parameters are valid

Stop category 0 and immediately cut off the power supply

This PFHp value means that only one hazardous failure may occur every one billion working hours, which is a very high level of safety in the field of industrial automation and can meet the highest safety requirements for automotive manufacturing, stamping equipment, robot workstations, and more.

2.2 Power Supply and Environment

Supply voltage: 24 V DC (PELV or SELV), allowable range 16.8 V... 30 V, residual ripple ≤ 2.4 V

Power consumption: ≤ 2.5 W

Working temperature: -25 ℃...+55 ℃, storage temperature: -25 ℃...+70 ℃

Protection level: IP20 (to be installed inside the control cabinet)

Humidity: ≤ 95%, no condensation

Engineers should be aware that this equipment is not suitable for outdoor or humid dusty environments and must be installed in cabinets that meet IP54 or higher standards.

2.3 Input Characteristics

The device provides the following input terminals:

2-channel secure input (S1, S2)

Adaptive sensor type: Safety sensors with potential isolated passive contacts (such as NC contacts for emergency stop buttons, NC/NO contacts for safety door switches)

High level threshold: 24 V DC (11 V... 30 V)

Low level threshold: 0 V DC (-3 V... 5 V)

Input current: 4 mA... 6 mA

Tolerance time between two start buttons: ≤ 3 seconds (for dual hand operation synchronous monitoring)

1-channel reset/EDM input (X1)

Function can be configured as: manual reset button input or external device monitoring feedback signal input

Electrical parameters are the same as safety inputs

3-channel test pulse output (T1, T2, T3)

Type: PNP semiconductor output, short circuit protection

Output voltage: ≥ Vd-3 V

Test pulse width: 2 ms

Test pulse interval: 40 ms

Function: Provide pulsed power supply for external safety sensors (such as safety carpets and light curtains) to detect cross circuit and short circuit faults

2.4 Output Characteristics

3 safety enable current paths (13-14, 23-24, 33-34)

Contact type: Positive guided N/O contact

Contact material: Silver alloy, gold-plated (suitable for low-level signals)

Switching voltage range: 10 V AC... 230 V AC/10 V DC... 230 V DC

Switching current range: 10 mA... 6 A (AC/DC universal)

Total current capacity: 12 A (sum of three contacts?)? The original text "Total current 12 A" should be understood as the maximum total current carried by all contacts simultaneously, with a maximum of 6 A per contact in reality

Mechanical lifespan: 1 × 10 ⁷ switching cycles

Overvoltage category: III (EN 60664-1)

Rated impulse withstand voltage Uimp: compliant with Class III

Response time (enable path disconnection): ≤ 12 ms (time from safety input disconnection to output contact opening)

2-channel application diagnostic output (Y1, Y2)

Type: Push pull semiconductor output, short circuit protection, non safety related

High level: ≥ V_s -3 V

Low level: ≤ 3 V

Output current capability: ≤ 120 mA (PNP), fill current ≤ 15 mA (NPN mode)

Purpose: Can be connected to PLC or indicator lights, used to display device status (such as safety output ON/OFF, faults, etc.)

Functional Configuration and Wiring Guide

All functions of RLY3-EMSS300 are configured through hard wired terminal connections without the need for software. The following is a typical method for setting up functions.

3.1 Reset Type Selection

The device supports two reset methods:

Automatic reset: When the safety input circuit is closed and the external device monitoring (EDM) conditions are met, the safety output is automatically restored. Suitable for situations where operator confirmation is not required (such as leaving after briefly entering an object in a light curtain protection area).

Manual reset: After the safety input is closed, the reset button (instantaneous contact) still needs to be pressed for the safety output to be connected. This is the standard requirement for most emergency stop and protective door applications to prevent accidental restarts.

Wiring method:

Manual reset: Connect the normally open contact of the reset button between terminals X1 and A2 (0V).

Automatic reset: Connect terminal X1 directly to A2 (short circuit).

Note: In manual reset mode, the device will monitor whether the pressing time of the reset button is within the valid range (usually 0.15 s to 2 s, but the data manual does not provide specific values, refer to the experience of similar devices). If the button gets stuck, the system will not start.

3.2 External Device Monitoring (EDM)

External device monitoring is used to detect whether downstream contactors or relays are disconnected as expected (i.e. feedback the status of the contacts). After the safety output is disconnected, the EDM input must detect the NC contact closure (or NO contact disconnection) of the downstream actuator within the specified time, otherwise the system will report an error and prohibit the next start.

When EDM is enabled:

Connect the forced guide NC contacts of the downstream contactor in series and connect them between X1 and A2.

At the same time, the reset button must not be connected to X1 again, as X1 is reused as an EDM input.

If EDM and manual reset need to be used simultaneously, the reset button must be connected in series with the EDM contact through external logic and connected to X1 (but the device itself does not support two independent functions and requires an external relay extension).

In RLY3-EMSS300, the X1 terminal is used for both reset and EDM, and cannot be used simultaneously. If the application requires EDM+manual reset, it is recommended to use other models of SICK or external circuits.

3.3 Differential monitoring and cross circuit detection

For dual channel safety sensors (such as emergency stop buttons with two NC contacts connected in series), the device is equipped with:

Differential monitoring: detect the time difference between two channels when switching states. If the difference time exceeds 3 seconds (for the reset button) or a specific set value, the device will enter a fault state.

Cross circuit detection: By testing the pulse output (T1/T2) to provide pulse signals of different phases to two channels, when the signals of the two channels are accidentally short circuited, the equipment recognizes a cross circuit fault and disconnects the safety output.

Wiring method (dual channel NC with cross circuit detection):

Connect T1 to the common terminal of the first NC contact and lead it from the normally closed terminal of the contact to the safety input S1.

Connect T2 to the common terminal of the second NC contact and lead it from the normally closed terminal of the contact to the safety input S2.

S1 and S2 are internally connected to logic, and the device automatically compares the two pulse signals.

If cross circuit detection is not required (for example, if the sensor already has fault monitoring, such as a type 4 light curtain), two NC contacts can be connected in series to S1 and A2 (single channel), but this can only reach Cat.2/PL c level.

3.4 Testing Pulse Output Usage

Three test pulse outputs (T1, T2, T3) can be used to power external sensors and achieve line monitoring. Each test pulse outputs a pulse sequence with a width of 2 ms and an interval of 40 ms. Attention: The test pulse output cannot directly drive high current loads and is only suitable for sensors or small relay coils.

Wiring rules:

Dual channel sensor: T1 → Channel 1 → S1, T2 → Channel 2 → S2.

Single channel sensor: T1 → sensor → S1, S2 short circuited to A2 or empty (dual channel monitoring needs to be turned off in the parameters, but hard wired devices have no parameters and need to be implemented through wiring).

Typical Application Circuit Example

4.1 Dual channel emergency stop monitoring, manual reset, with EDM

Components:

1 dual channel emergency stop button (2NC)

1 reset button (NO)

2 contactors (with forced guiding NC contacts)

Wiring:

Power supply: A1 is connected to+24V, A2 is connected to 0V.

Test pulse: T1 is connected to emergency stop channel 1 NC input, T2 is connected to emergency stop channel 2 NC input. Connect NC to S1 and S2 respectively.

Reset/EDM: Connect the NC feedback contacts of two contactors in series, then connect them in series with the NO contact of the reset button, and finally connect them between X1 and A2.

Safe output: Three enable paths (13-14, 23-24, 33-34) are connected in series to the contactor coil circuit.

Work logic:

When the emergency stop is not pressed, both S1 and S2 are at high level (pulses from T1/T2).

Press the reset button and the feedback contact of the contactor is closed (i.e. the contactor has been disconnected), then the device is connected to the safety output and the contactor is closed.

Press the emergency stop button, and the safety output will immediately disconnect (≤ 12ms), causing the contactor to lose power.

If the contactor contacts are stuck, EDM will detect that the feedback contacts are not closed during the next start-up, prevent start-up, and report an error.

4.2 Protective door monitoring (single channel, automatic reset)

Applicable scenario: Non highest safety level, protective door switch is single NC.

Wiring:

T1 → Door switch NC in, NC out → S1. S2 is empty or short circuited to A2 (to ensure that the equipment can recognize single channel mode, the actual RLY3-EMSS300 supports single channel, but the security level has been lowered to Cat. 2).

Short circuit X1 to A2 (automatic reset).

Secure output connection actuator.

Attention: Single channel without cross circuit detection cannot detect wire short circuit faults and is only suitable for low-risk applications.

4.3 Two handed operation box (compliant with EN 574 Type IIIc)

Requirement: Both buttons must be pressed simultaneously within 0.5 seconds, and there must be no crossover circuit between them.

Wiring:

T1 → button 1 NO in, NO out → S1.

T2 → button 2 NO in, NO out → S2.

Do not use reset (automatic reset, as the dual hand operation box itself requires simultaneous pressing after each release).

Short circuit X1 to A2.

Safety output control press clutch, etc.

The built-in differential monitoring of the device (3 seconds) is sufficient for manual operation (0.5 second synchronization requirement). If stricter 0.5-second monitoring is required, external processing or the use of a dedicated dual hand control module is necessary.

Troubleshooting and Diagnosis

5.1 Meaning of LED indicator lights

The RLY3-EMSS300 panel is equipped with multiple LEDs for rapid diagnosis (the color and definition of each LED are not detailed in the data manual, but according to the rules of similar SICK products, they usually include):

PWR (green): The power supply is normal.

IN1/IN2: Safe input status (lit to indicate high input).

OUT: Safe output status (lit to indicate closed enable path).

ERR (red): Fault status (such as differential timeout, crossover circuit, EDM feedback error, etc.).

When ERR lights up, the device will lock the safety output until the fault is resolved and a reset is performed.

5.2 Common Fault Phenomena and Causes

Troubleshooting steps for possible causes of fault phenomena

After power on, the safety output cannot be connected, and the ERR constant light configuration is incorrect. If X1 is suspended or wired incorrectly, check whether X1 is wired correctly according to the required reset method (short circuit for automatic reset, button for manual reset, and button for normally open contact).

After pressing the reset button, the safety output is instantly connected and disconnected. If no feedback signal is received within the EDM time window, check whether the downstream contactor NC contact is closed. If the contactor coil has not been energized, the feedback contact should be closed (because the contactor is in an open state). Verify the wiring of the feedback loop.

The safety output sometimes does not respond, and the ERR flashing differential monitoring or crossover circuit detects intermittent faults. Check whether the contacts of the two safety input channels switch synchronously. Observe the T1/S1 and T2/S2 waveforms with an oscilloscope to see if there are any unexpected short circuits or open circuits.

When there is no fault, the safety output still cannot be connected. If the reset button is stuck or the normally open contact does not return normally, the voltage between X1 and A2 should be measured as 0V (automatic reset) or only jump to high level when pressed. If it remains high, the button will stick.

The emergency stop was not pressed but the safety output was disconnected. Internal self inspection revealed a fault, such as the failure of the output contact forced guiding mechanism to replace the equipment. Attention: Forced guiding contacts may experience mechanical jamming at the end of their lifecycle.

5.3 Response time verification

The nominal response time of the device (enable path disconnection) is ≤ 12 ms. This is the time from the disconnection of the safety input (such as the opening of the emergency stop contact) to the actual opening of the output contact. When designing a safe distance (such as the distance from a light curtain to a hazard source), engineers must accumulate this time with sensor response time, actuator action time, and controller delay.

Calculation formula:

T total=T sensor+TRLY three+T contactor+T braking 

T total=T sensor+T RLY3+T contactor+T braking

Example: Assuming an emergency stop sensor response time of 5 ms, RLY3-EMSS300 maximum of 12 ms, contactor release time of 20 ms, and braking time of 50 ms, the total shutdown time is approximately 87 ms. According to ISO 13855, the safety distance

S=K×T+C

S=K × T+C, where K=1600 mm/s, then S ≥ 1600 × 0.087+C ≈ 139 mm+C. This value needs to be compared with the specific application.

5.4 Effects of Test Pulses

Test pulse width of 2 ms with an interval of 40 ms. These pulses appear on T1/T2/T3 and may be mistaken for signal jitter by some fast response electronic sensors. For electromechanical contact sensors (emergency stop, door switch), a 2 ms pulse will not cause contact misoperation because the bounce time of mechanical contacts is usually greater than 2 ms. If a solid-state output safety light curtain is connected, it is necessary to confirm whether its output can tolerate test pulses, otherwise cross circuit detection should be disabled (changed to single channel or use pulse free power supply).

Certification, Standards, and Compliance

RLY3-EMSS300 holds the following important certifications to ensure its availability in major global markets:

EU Declaration of Conformity (CE)

UK Declaration of Conformity (UKCA)

ACMA Declaration of Conformity (Australia)

CULus Certificate (North America)

CCC Certificate (China)

UK Type Examination Approval

China RoHS Compliance

Its electromagnetic compatibility complies with IEC 61000-6-4 (emission), IEC 61326-3-1 (immunity, industrial applications), IEC 61000-6-2, and IEC 60947-5-1. Users can integrate into standard industrial environments without the need for additional EMC testing.

Alternative and selection suggestions

When encountering equipment replacement or new project selection, attention should be paid to:

RLY3-EMSS300 has a single width of 18mm, which can save control cabinet space.

If the application requires independent manual reset and EDM to coexist, please choose other SICK models (such as RLY3-OSSD series).

If the safety sensor is of OSSD output type (such as light curtain), RLY3-EMSS300 is not suitable because its input requires passive contacts. At this time, RLY3-OSSD or UE series should be selected.

The attachment information can be found at www.sick.com/ReLy.

Maintenance and lifespan management

Despite the device's task time of up to 20 years, regular functional testing is still required:

Trigger each safety function at least once a month (press emergency stop, open protective door), confirm that the safety output is reliably disconnected and the reset logic is normal.

Check the LED indicator lights to ensure there are no abnormal flashes.

Measure the contact resistance of the safety output contacts with a multimeter once a year. If it exceeds 100 m Ω and the switching frequency is high, preventive replacement should be considered.

For outputs directly connected to inductive loads (contactor coils), freewheeling diodes or surge suppressors should be connected in parallel at both ends of the load to extend the contact life.