In the field of electrical control systems, relays serve as essential switching components that bridge the gap between low-voltage control circuits and high-voltage load circuits, enabling precise, safe, and efficient control of electrical equipment. Among the diverse range of relays available, the Call&Reset Relay (also known as Call and Reset Relay) stands out for its unique bistable operation mechanism, which requires separate call (activation) and reset (deactivation) commands to switch and maintain its operating state. Unlike monostable relays that return to their default state once the control signal is removed, Call&Reset Relays remain in their activated state until a dedicated reset signal is received, making them ideal for applications that demand latching control, status retention, and centralized management of electrical devices.

With the rapid advancement of industrial automation, smart building technology, medical equipment, and infrastructure construction, the demand for reliable and flexible control components has grown exponentially. Call&Reset Relays have emerged as a critical solution in scenarios where remote activation, local indication, and controlled deactivation are essential—such as nurse call systems in hospitals, emergency alarm systems in commercial buildings, access control systems in residential complexes, and equipment control in industrial plants. This article aims to provide a comprehensive overview of Call&Reset Relays, including their basic definition, working principles, classification, core characteristics, key technical parameters, practical applications across various industries, installation and maintenance considerations, and future development trends. By delving into these aspects, this article seeks to help engineers, technicians, and industry professionals gain a deeper understanding of this specialized relay and leverage its capabilities to optimize electrical control systems.

1. Overview of Call&Reset Relay

1.1 Definition and Basic Concept

A Call&Reset Relay is a type of bistable electromechanical or electronic relay designed to operate in two distinct stable states: the “normal” (deactivated) state and the “called” (activated) state. The relay is triggered into the activated state by a “call” signal (also referred to as a set signal), which can be generated by a momentary switch, sensor, or remote control device. Once activated, the relay latches into this state and remains there indefinitely, even if the call signal is removed. To return the relay to its normal deactivated state, a separate “reset” signal is required—this signal is typically applied to a dedicated reset terminal and can be manual (e.g., a pushbutton) or automatic (e.g., a signal from a central control system).

The core distinction between Call&Reset Relays and other types of relays (such as monostable relays or time-delay relays) lies in their bistable latching behavior. Monostable relays rely on a continuous control signal to maintain their activated state; if the signal is interrupted, they immediately reset to their default state. In contrast, Call&Reset Relays eliminate the need for a continuous control signal, reducing power consumption and improving system reliability in applications where long-term state retention is required. This latching mechanism also ensures that the relay’s output state is not affected by temporary power fluctuations or signal interruptions, making it suitable for critical control applications.

1.2 Core Components and Structure

The structure of a Call&Reset Relay varies slightly depending on whether it is electromechanical or electronic, but both types share several core components that enable their unique functionality. Below is a detailed breakdown of the key components:

1.2.1 Electromechanical Call&Reset Relay Components

Electromechanical Call&Reset Relays are the most common type, widely used in industrial and commercial applications due to their simplicity, durability, and compatibility with a wide range of voltage and current ratings. Their core components include:

Coil Assembly: The coil is the primary component responsible for generating the magnetic force needed to activate the relay. Unlike monostable relays, which have a single coil, many electromechanical Call&Reset Relays feature two separate coils: a “call coil” (set coil) and a “reset coil.” When voltage is applied to the call coil, it generates a magnetic field that pulls the armature towards it, switching the relay into the activated state. When voltage is applied to the reset coil, it generates an opposing magnetic field that releases the armature, returning the relay to its deactivated state. Some models use a single coil with polarity reversal to achieve both call and reset functions, but dual-coil designs are more common due to their simplicity and reliability.
Armature and Contact System: The armature is a movable metal component that is attracted by the magnetic field generated by the coil. Attached to the armature is a set of electrical contacts, which are responsible for switching the load circuit. Call&Reset Relays typically feature either Single-Pole Double-Throw (SPDT) or Double-Pole Double-Throw (DPDT) contact configurations. The contacts are divided into three types: Normally Open (NO), Normally Closed (NC), and Common (COM). In the deactivated state, the NC contacts are closed, and the NO contacts are open. When the relay is activated by a call signal, the armature moves, opening the NC contacts and closing the NO contacts—this state is latched until a reset signal is received.
Latching Mechanism: The latching mechanism is the key component that enables the relay to remain in its activated state without a continuous call signal. In electromechanical models, this mechanism typically consists of a mechanical latch (such as a pawl and ratchet system) that locks the armature in place once it is activated. The reset coil generates enough magnetic force to release the latch, allowing the armature to return to its original position. Some advanced models use a permanent magnet to provide latching, reducing the power consumption of the relay.
Terminal Block: The terminal block provides connection points for the call coil, reset coil, contact system, and load circuit. It is designed to facilitate easy wiring and installation, with clear labeling to distinguish between call, reset, COM, NO, and NC terminals. Most industrial-grade Call&Reset Relays feature screw terminals or spring-clamp terminals, which ensure secure connections and resistance to vibration.
Housing: The housing is typically made of flame-retardant plastic (such as PA66 or ABS) that provides electrical insulation and protection against dust, moisture, and physical damage. The housing also helps to contain the magnetic field generated by the coil, reducing electromagnetic interference (EMI) with other components in the control system. Many models are designed for 35mm DIN rail mounting (in accordance with EN 60715 standard), which is the industry standard for mounting electrical components in control panels.

1.2.2 Electronic Call&Reset Relay Components

Electronic Call&Reset Relays (also known as solid-state Call&Reset Relays) use electronic components (such as transistors, thyristors, and integrated circuits) instead of mechanical contacts to switch the load circuit. They are ideal for applications that require fast switching speeds, low noise, and long service life. Their core components include:

Control Circuit: The control circuit consists of integrated circuits (ICs) that process the call and reset signals. It includes a latching circuit (such as a flip-flop) that retains the relay’s state once activated. The control circuit is designed to accept a wide range of input signals, including DC voltage (5V, 12V, 24V), AC voltage (110V, 220V), and digital signals (from microcontrollers or PLCs).
Solid-State Switching Elements: Instead of mechanical contacts, electronic Call&Reset Relays use solid-state switching elements such as MOSFETs (for DC loads) or TRIACs (for AC loads). These elements provide fast switching speeds (microseconds to milliseconds) and have no moving parts, eliminating wear and tear and reducing noise. Solid-state switches also have a longer service life than mechanical contacts, making them suitable for high-cycle applications.
Input Interface: The input interface converts the call and reset signals into a format that can be processed by the control circuit. It may include rectifiers (for AC input signals), voltage regulators (to stabilize the input voltage), and optocouplers (to provide electrical isolation between the input and output circuits). Optocouplers prevent noise from the load circuit from interfering with the control circuit, improving system reliability.
Output Protection: Electronic Call&Reset Relays often include output protection features such as overcurrent protection (using fuses or current-limiting resistors), overvoltage protection (using varistors or zener diodes), and surge protection (to protect against voltage spikes). These features help to prevent damage to the relay and the load circuit.
Status Indicator: Most electronic Call&Reset Relays include an LED status indicator that shows whether the relay is in the activated (called) or deactivated (reset) state. This makes it easy for technicians to monitor the relay’s operation during installation and maintenance.

2. Working Principle of Call&Reset Relay

The working principle of a Call&Reset Relay is based on bistable latching, which involves two stable states and requires separate signals to switch between them. The exact operation varies slightly between electromechanical and electronic models, but the core logic remains the same: a call signal activates the relay and latches it in the activated state, while a reset signal deactivates it and returns it to the default state. Below is a detailed explanation of the working principle for both types:

2.1 Working Principle of Electromechanical Call&Reset Relay

Electromechanical Call&Reset Relays use magnetic force and mechanical latching to achieve their bistable operation. The process can be divided into three key stages: deactivated state, activation (call) state, and deactivation (reset) state.

2.1.1 Deactivated State (Default State)

In the deactivated state, no voltage is applied to either the call coil or the reset coil. The mechanical latch is in its default position, holding the armature away from the call coil. As a result, the NC contacts are closed, and the NO contacts are open. The load circuit connected to the NC contacts is energized, while the load circuit connected to the NO contacts is de-energized (or vice versa, depending on the application).

2.1.2 Activation (Call) State

When a call signal is applied to the call coil (e.g., by pressing a momentary pushbutton), voltage flows through the coil, generating a magnetic field. The magnetic force attracts the armature towards the coil, causing the contacts to switch: the NC contacts open, and the NO contacts close. This switches the load circuit to the desired state (e.g., activating an alarm, turning on a light, or starting a motor).

As the armature moves, the mechanical latch engages, locking the armature in the activated position. This latching mechanism ensures that the relay remains in the activated state even after the call signal is removed (i.e., the pushbutton is released). The magnetic field generated by the call coil is only needed momentarily to activate the relay; once latched, no power is required to maintain the activated state, reducing power consumption.

2.1.3 Deactivation (Reset) State

To deactivate the relay, a reset signal is applied to the reset coil. The reset coil generates an opposing magnetic field that overcomes the force of the mechanical latch, releasing the armature. The armature then returns to its original position under the force of a return spring, switching the contacts back to their default state: the NC contacts close, and the NO contacts open. The load circuit is thus returned to its original state, and the relay is ready to be activated again by a new call signal.

It is important to note that the call and reset signals must be applied separately—applying both signals simultaneously will not damage the relay, but it will not change the relay’s state. Some electromechanical Call&Reset Relays feature a manual reset button on the housing, which allows technicians to reset the relay without applying a voltage signal to the reset coil.

2.2 Working Principle of Electronic Call&Reset Relay

Electronic Call&Reset Relays use solid-state components and digital logic to achieve bistable latching, eliminating the need for mechanical moving parts. The core of the electronic relay is a latching circuit (typically a SR flip-flop), which has two stable states: SET (activated) and RESET (deactivated). The flip-flop is controlled by two input signals: a SET (call) signal and a RESET signal.

2.2.1 Deactivated State (Default State)

In the deactivated state, the flip-flop is in the RESET state. The control circuit outputs a low signal to the solid-state switching element (MOSFET or TRIAC), turning it off. As a result, the load circuit connected to the output is de-energized. The LED status indicator (if present) is off, indicating that the relay is in the deactivated state.

2.2.2 Activation (Call) State

When a call (SET) signal is applied to the input interface, the signal is processed by the control circuit (e.g., rectified, filtered, and amplified) and sent to the flip-flop. The SET signal triggers the flip-flop to switch to the SET state, which outputs a high signal to the solid-state switching element. This turns on the switching element, energizing the load circuit.

The flip-flop retains the SET state even after the call signal is removed, ensuring that the relay remains activated. This latching behavior is achieved through the internal logic of the flip-flop, which stores the state until a RESET signal is received. The LED status indicator turns on, showing that the relay is in the activated state.

2.2.3 Deactivation (Reset) State

When a reset signal is applied to the input interface, the control circuit processes the signal and sends it to the flip-flop. The RESET signal triggers the flip-flop to switch back to the RESET state, outputting a low signal to the solid-state switching element. This turns off the switching element, de-energizing the load circuit. The LED status indicator turns off, indicating that the relay is back in the deactivated state.

Electronic Call&Reset Relays offer several advantages over electromechanical models in terms of operation: they have faster switching speeds, no mechanical wear, lower noise, and are more resistant to vibration and shock. They also offer greater flexibility in terms of input signals, as they can accept digital signals from microcontrollers, PLCs, or sensors, making them ideal for smart control systems.

3. Classification of Call&Reset Relay

Call&Reset Relays can be classified into several categories based on different criteria, including their construction type, contact configuration, voltage rating, control method, and application. Understanding these classifications is essential for selecting the right relay for a specific application. Below is a detailed breakdown of the main classifications:

3.1 Classification by Construction Type

This is the most basic classification, dividing Call&Reset Relays into two main types: electromechanical and electronic.

3.1.1 Electromechanical Call&Reset Relay

As discussed earlier, electromechanical Call&Reset Relays use mechanical moving parts (armature, contacts, latch) and magnetic coils to achieve switching. They are characterized by: Simple structure and low costHigh current and voltage ratings (suitable for heavy-duty loads)Compatibility with both AC and DC load circuitsMechanical wear over time (reduced service life compared to electronic models)Noise generated during contact switching

Electromechanical Call&Reset Relays are widely used in industrial control systems, emergency alarm systems, and automotive applications, where high current handling capability and durability are prioritized.

3.1.2 Electronic Call&Reset Relay

Electronic Call&Reset Relays use solid-state components (transistors, TRIACs, ICs) and digital logic to achieve switching, with no mechanical moving parts. They are characterized by: Fast switching speeds (microseconds to milliseconds)Low noise (no contact bounce or mechanical vibration)Long service life (no mechanical wear)High resistance to vibration and shockCompatibility with digital control signals (microcontrollers, PLCs)Higher cost compared to electromechanical models

Electronic Call&Reset Relays are ideal for applications that require high reliability, fast switching, and low noise, such as medical equipment, smart buildings, and precision industrial automation.

3.2 Classification by Contact Configuration

The contact configuration of a Call&Reset Relay refers to the number of poles (input/output circuits) and throws (switch positions) of the contact system. The most common configurations are:

3.2.1 Single-Pole Double-Throw (SPDT)

SPDT Call&Reset Relays have one common (COM) terminal, one normally open (NO) terminal, and one normally closed (NC) terminal. They are used to switch a single load circuit between two states (e.g., on/off). This is the most common contact configuration for Call&Reset Relays, suitable for simple control applications such as activating an alarm or turning on a light. Many industrial models, such as the EKR 8-2 series from ETEK Electric, feature SPDT contact configurations with current ratings ranging from 5A to 16A.

3.2.2 Double-Pole Double-Throw (DPDT)

DPDT Call&Reset Relays have two common (COM) terminals, two normally open (NO) terminals, and two normally closed (NC) terminals. They are used to switch two independent load circuits simultaneously. This configuration is ideal for applications that require synchronized control of two devices, such as dual alarm systems or redundant load circuits. The EKR 8-2 series also includes DPDT models, providing flexibility for more complex control scenarios.

3.2.3 Single-Pole Single-Throw (SPST)

SPST Call&Reset Relays have one common (COM) terminal and one normally open (NO) or normally closed (NC) terminal. They are used for simple on/off control of a single load circuit. While less common than SPDT configurations, SPST Call&Reset Relays are suitable for applications where only one switching state is required (e.g., activating a single indicator light).

3.3 Classification by Voltage Rating

Call&Reset Relays are classified based on their rated coil voltage (input voltage for activating the relay) and rated contact voltage (output voltage for switching the load circuit).

3.3.1 Coil Voltage Rating

The coil voltage rating refers to the voltage required to activate the call or reset coil. Common coil voltage ratings include: DC voltage: 5V, 12V, 24V, 48V (commonly used in industrial automation and automotive applications)AC voltage: 110V, 220V, 380V (commonly used in commercial and residential control systems)

It is important to select a relay with a coil voltage rating that matches the control signal voltage to ensure reliable activation. For example, a 12V DC Call&Reset Relay should be used with a 12V DC call/reset signal.

3.3.2 Contact Voltage Rating

The contact voltage rating refers to the maximum voltage that the contacts can safely switch. Common contact voltage ratings include: DC voltage: Up to 240V DC (for electronic loads such as motors and solenoids)AC voltage: Up to 400V AC (for AC loads such as lights, pumps, and heaters)

The contact voltage rating must be higher than the voltage of the load circuit to prevent contact arcing and damage to the relay. For example, a relay with a 250V AC contact rating should not be used with a 380V AC load.

3.4 Classification by Control Method

Call&Reset Relays can also be classified based on the method used to apply the call and reset signals:

3.4.1 Manual Control Call&Reset Relay

Manual control Call&Reset Relays require human intervention to apply the call and reset signals. This is typically done using momentary pushbuttons: one pushbutton for the call signal and another for the reset signal. These relays are commonly used in applications where local control is required, such as emergency stop buttons, nurse call stations, and manual equipment control panels.

3.4.2 Automatic Control Call&Reset Relay

Automatic control Call&Reset Relays receive call and reset signals from automatic devices such as sensors, microcontrollers, PLCs, or remote control systems. No human intervention is required for activation or deactivation. These relays are ideal for industrial automation, smart buildings, and remote monitoring systems, where control signals are generated automatically based on predefined conditions (e.g., temperature, pressure, or time).

3.4.3 Hybrid Control Call&Reset Relay

Hybrid control Call&Reset Relays support both manual and automatic control. They can be activated/deactivated by either a manual pushbutton or an automatic signal, providing flexibility in control. These relays are commonly used in critical applications where redundancy is required, such as emergency alarm systems (where automatic activation is preferred, but manual control is available as a backup).

4. Core Characteristics and Technical Parameters of Call&Reset Relay

To select the right Call&Reset Relay for a specific application, it is essential to understand its core characteristics and key technical parameters. These parameters determine the relay’s performance, reliability, and compatibility with the control and load circuits. Below is a detailed overview of the most important characteristics and parameters:

4.1 Core Characteristics

4.1.1 Bistable Latching

As the defining characteristic of Call&Reset Relays, bistable latching ensures that the relay remains in its activated state until a dedicated reset signal is received. This eliminates the need for a continuous control signal, reducing power consumption and improving system reliability. The latching mechanism (mechanical or electronic) must be robust enough to withstand vibration, shock, and power fluctuations to maintain the relay’s state.

4.1.2 Electrical Isolation

Call&Reset Relays provide electrical isolation between the control circuit (call/reset signals) and the load circuit. This isolation prevents high voltage from the load circuit from interfering with the low-voltage control circuit, protecting sensitive components (such as microcontrollers and sensors) and ensuring operator safety. Electromechanical relays achieve isolation through the physical separation of the coil and contacts, while electronic relays use optocouplers or transformers.

4.1.3 Contact Rating (Current and Voltage)

The contact rating refers to the maximum current and voltage that the relay’s contacts can safely switch. This is a critical parameter, as exceeding the contact rating can cause contact arcing, overheating, and damage to the relay. For example, the Finder 13.12 Call&Reset Relay has a contact current rating of 8A and a maximum switching voltage of 400V AC, making it suitable for switching incandescent lamp loads up to 800W.

4.1.4 Switching Speed

Switching speed refers to the time it takes for the relay to switch from the deactivated state to the activated state (call time) and vice versa (reset time). Electromechanical relays have slower switching speeds (typically 10-50 milliseconds), while electronic relays have faster switching speeds (microseconds to milliseconds). Switching speed is important in applications that require fast response times, such as emergency alarm systems and precision industrial automation.

4.1.5 Service Life

Service life refers to the number of switching cycles that the relay can perform before failing. Electromechanical relays have a limited service life (typically 100,000 to 1,000,000 cycles) due to mechanical wear of the contacts and armature. Electronic relays have a much longer service life (up to 100,000,000 cycles) because they have no moving parts. The service life of the relay is also affected by the load current, voltage, and operating environment (temperature, humidity, vibration).

4.1.6 Noise and EMI

Electromechanical Call&Reset Relays generate noise during contact switching (contact bounce) and when the coil is energized/de-energized. This noise can cause electromagnetic interference (EMI) with other components in the control system. Electronic relays generate no mechanical noise and produce less EMI, making them suitable for applications that require low noise, such as medical equipment and audio systems.

4.2 Key Technical Parameters

4.2.1 Coil Parameters

Coil Voltage (Vc): The rated voltage required to activate the call or reset coil. Common values include 5V DC, 12V DC, 24V DC, 110V AC, and 220V AC. Some relays have a wide voltage range (e.g., 12-240V AC/DC) for greater flexibility.
Coil Current (Ic): The current drawn by the coil when energized. This parameter is important for selecting the appropriate power supply for the control circuit.
Coil Resistance (Rc): The resistance of the coil, calculated using Ohm’s Law (Rc = Vc / Ic). This parameter helps to verify the coil’s integrity during maintenance.
Pick-Up Voltage: The minimum voltage required to activate the coil and switch the relay. This is typically 80-90% of the rated coil voltage.
Drop-Out Voltage: The minimum voltage at which the coil de-energizes and the relay resets (for monostable relays; not applicable to Call&Reset Relays due to latching).

4.2.2 Contact Parameters

Contact Configuration: As discussed earlier, common configurations include SPDT, DPDT, and SPST. The Finder 13.12 model features 1 CO (SPDT) + 1 NO (SPST-NO) contacts, providing flexibility for both switching and indication applications.
Contact Current Rating (Ic): The maximum current that the contacts can safely carry continuously. Common values range from 1A to 30A. For example, the EKR 8-2 series offers models with 5A and 16A contact current ratings.
Contact Voltage Rating (Vc): The maximum voltage that the contacts can safely switch. Common values include 250V AC, 400V AC, and 240V DC.
Contact Resistance: The resistance of the closed contacts, typically measured in milliohms (mΩ). Low contact resistance ensures minimal voltage drop across the contacts, reducing power loss and overheating.
Arcing Voltage: The voltage at which arcing occurs between the contacts when they open. Arcing can damage the contacts over time, so relays with higher arcing voltage ratings are more durable.

4.2.3 Environmental Parameters

Operating Temperature Range: The range of temperatures in which the relay can operate reliably. Common ranges are -40°C to +85°C for industrial-grade relays and -10°C to +60°C for commercial-grade relays.
Storage Temperature Range: The range of temperatures in which the relay can be stored without damage. This is typically wider than the operating temperature range.
Humidity: The maximum relative humidity that the relay can withstand, typically 95% (non-condensing) for industrial applications.
Vibration and Shock Resistance: The ability of the relay to withstand vibration and shock without damage or state change. Industrial-grade relays are typically rated for vibration up to 10g and shock up to 100g.
Protection Class: The degree of protection against dust and moisture, as defined by the IP (Ingress Protection) rating. Common ratings for Call&Reset Relays include IP20 (protection against solid objects larger than 12mm) and IP67 (fully waterproof and dustproof) for harsh environments.

4.2.4 Other Parameters

Mounting Type: The method used to mount the relay. Common mounting types include DIN rail mounting (35mm, EN 60715 standard), panel mounting, and PCB mounting. Most industrial Call&Reset Relays are designed for DIN rail mounting, which facilitates easy installation and maintenance in control panels.
Weight: The weight of the relay, which is important for applications where space and weight are limited (e.g., automotive and aerospace).
Approval Certifications: Certifications such as CE (European Conformity), UL (Underwriters Laboratories), and RoHS (Restriction of Hazardous Substances) ensure that the relay meets international safety and environmental standards. For example, the Finder 13 series relays are CE certified, ensuring compliance with European safety standards.

5. Applications of Call&Reset Relay

Call&Reset Relays are versatile components with a wide range of applications across various industries, thanks to their bistable latching mechanism, electrical isolation, and flexible control options. They are particularly well-suited for applications that require remote activation, state retention, and centralized reset. Below is a detailed overview of their key applications in different industries:

5.1 Medical Equipment Industry

The medical equipment industry requires highly reliable and safe control components, and Call&Reset Relays play a critical role in ensuring the proper operation of medical devices. Key applications include:

5.1.1 Nurse Call Systems

Nurse call systems are essential in hospitals, care homes, and assisted living facilities, allowing patients to summon assistance quickly and easily. Call&Reset Relays are used to activate the call signal when a patient presses a call button (call signal) and to reset the signal once assistance has been provided (reset signal from the nurse station). The latching mechanism ensures that the call signal remains active until the nurse resets it, preventing missed calls. For example, the Finder 13.12 Call&Reset Relay is specifically designed for attendant call systems in hospitals and care homes, featuring dual outputs for remote alarm signals and local activation indication. The relay’s ability to handle cable runs up to 100m allows multiple units to be centralized in a control panel, simplifying maintenance and saving space.

5.1.2 Medical Device Control

Call&Reset Relays are used in various medical devices, such as patient monitors, infusion pumps, and defibrillators, to control critical functions. For example, in an infusion pump, a call signal can activate the pump to start delivering medication, and a reset signal can stop the pump once the infusion is complete. The electrical isolation provided by the relay protects sensitive electronic components in the medical device from high-voltage interference, ensuring patient safety. Electronic Call&Reset Relays are preferred in this application due to their low noise and long service life, which is essential for continuous operation in medical environments.

5.2 Industrial Automation Industry

Industrial automation relies on precise and reliable control of machinery and equipment, and Call&Reset Relays are widely used in control panels, PLC systems, and sensor networks. Key applications include:

5.2.1 Emergency Stop Systems

Emergency stop (E-stop) systems are critical for ensuring the safety of workers in industrial environments. Call&Reset Relays are used to activate the E-stop signal when an emergency stop button is pressed (call signal), which shuts down machinery or equipment immediately. The relay latches the E-stop state, preventing the machinery from restarting until a reset signal is applied (typically by a trained technician). This ensures that the machinery remains off until the emergency is resolved, reducing the risk of accidents. Electromechanical Call&Reset Relays are preferred in this application due to their high current handling capability and durability.

5.2.2 Equipment Control and Status Monitoring

Call&Reset Relays are used to control the operation of industrial equipment, such as motors, pumps, conveyors, and heaters. For example, a call signal from a sensor (e.g., a temperature sensor indicating that the temperature is too high) can activate a relay to turn on a cooling fan, and a reset signal (when the temperature returns to normal) can turn off the fan. The latching mechanism ensures that the fan remains on until the temperature is corrected, even if the sensor signal is temporarily interrupted. Call&Reset Relays are also used to monitor the status of equipment, with the relay’s state indicating whether the equipment is running or stopped. This information can be transmitted to a central control system for remote monitoring.

5.2.3 Production Line Control

In production lines, Call&Reset Relays are used to control the sequence of operations. For example, a call signal can start a production cycle, and a reset signal can end the cycle once the product is completed. The relay latches the production state, ensuring that the cycle is not interrupted by temporary power fluctuations or signal errors. This improves the efficiency and reliability of the production line, reducing downtime and waste.

5.3 Smart Building and Construction Industry

Smart buildings require intelligent control of lighting, HVAC (Heating, Ventilation, and Air Conditioning), security, and other systems, and Call&Reset Relays are essential components in these systems. Key applications include:

5.3.1 Lighting Control Systems

Call&Reset Relays are used in lighting control systems for commercial and residential buildings, allowing users to activate lights with a call signal (e.g., a motion sensor or wall switch) and reset them with a dedicated reset signal (e.g., a timer or manual switch). The latching mechanism ensures that the lights remain on until the reset signal is applied, reducing energy consumption by preventing lights from being left on accidentally. For example, in public toilets and bathrooms, Call&Reset Relays are used to activate lights when a user enters (call signal) and reset them when the user leaves (reset signal), ensuring that lights are only on when needed.

5.3.2 Security and Access Control Systems

Call&Reset Relays are used in security systems, such as alarm systems and access control systems. For example, in an access control system, a call signal from a card reader or keypad can activate a relay to unlock a door, and a reset signal (after a predetermined time or when the door is closed) can lock the door again. The latching mechanism ensures that the door remains unlocked until the reset signal is applied, providing secure access control. In alarm systems, a call signal from a motion sensor or door contact can activate the alarm, and a reset signal from a key fob or control panel can deactivate it.

5.3.3 HVAC Control Systems

Call&Reset Relays are used in HVAC systems to control heating, cooling, and ventilation equipment. For example, a call signal from a thermostat (indicating that the temperature is below the set point) can activate a relay to turn on the heater, and a reset signal (when the temperature reaches the set point) can turn off the heater. The latching mechanism ensures that the heater remains on until the temperature is correct, improving energy efficiency and comfort.

5.4 Automotive Industry

The automotive industry uses Call&Reset Relays in various applications, where they are exposed to harsh environments (vibration, temperature extremes, moisture) and require high reliability. Key applications include:

5.4.1 Automotive Alarm Systems

Call&Reset Relays are used in automotive alarm systems to activate the alarm when a call signal is received (e.g., from a door sensor, hood sensor, or remote control) and to reset the alarm when a reset signal is applied (e.g., from a key fob or ignition switch). The latching mechanism ensures that the alarm remains active until the reset signal is received, deterring theft.

5.4.2 Power Window and Door Lock Control

Call&Reset Relays are used to control power windows and door locks in modern vehicles. For example, a call signal from the window switch can activate a relay to lower the window, and a reset signal (when the switch is released or the window reaches the bottom) can stop the motor. The latching mechanism ensures that the window motor stops at the correct position, preventing damage.

5.4.3 Lighting Control

Call&Reset Relays are used to control automotive lighting, such as headlights, taillights, and interior lights. For example, a call signal from the headlight switch can activate a relay to turn on the headlights, and a reset signal (when the switch is turned off or the ignition is turned off) can turn them off. The latching mechanism ensures that the headlights remain on until the reset signal is applied, improving safety during nighttime driving.

5.5 Other Applications

In addition to the industries mentioned above, Call&Reset Relays are used in a variety of other applications, including:

Emergency Alarm Systems: In commercial buildings, schools, and public spaces, Call&Reset Relays are used to activate emergency alarms (e.g., fire alarms) when a call signal is received (e.g., from a fire alarm pull station) and to reset them when the emergency is resolved. For example, in floor fire safety alarm systems, the fire alarm switch on each floor acts as the call switch (can only be turned on), and the reset switch is installed in the control room under supervision.
Home Automation Systems: In smart homes, Call&Reset Relays are used to control various devices, such as smart speakers, thermostats, and security cameras, allowing users to activate and deactivate them remotely.
Test and Measurement Equipment: Call&Reset Relays are used in test and measurement equipment to control the switching of test signals, ensuring accurate and reliable measurements.
Renewable Energy Systems: In solar and wind energy systems, Call&Reset Relays are used to control the charging and discharging of batteries, ensuring the safe and efficient operation of the system.

6. Installation, Maintenance, and Troubleshooting of Call&Reset Relay

Proper installation, regular maintenance, and effective troubleshooting are essential for ensuring the reliable operation of Call&Reset Relays. Below is a detailed guide to these aspects:

6.1 Installation Guidelines

When installing a Call&Reset Relay, it is important to follow these guidelines to ensure proper operation and safety:

6.1.1 Mounting

Select a mounting location that is free from dust, moisture, vibration, and extreme temperatures. The location should also provide easy access for wiring and maintenance.
For DIN rail-mounted relays, ensure that the DIN rail is properly secured to the control panel and that the relay is firmly clipped onto the rail. Most Call&Reset Relays are designed for 35mm DIN rails (EN 60715 standard), which is the industry standard.
For panel-mounted relays, use the appropriate screws to secure the relay to the panel, ensuring that the screws are tight to prevent vibration.
For PCB-mounted relays, solder the relay’s pins to the PCB carefully, ensuring that there are no cold solder joints (which can cause poor connections).

6.1.2 Wiring

Before wiring, ensure that the power to the control and load circuits is turned off to prevent electric shock.
Follow the relay’s wiring diagram (typically provided on the relay’s housing or in the datasheet) to connect the call coil, reset coil, contacts, and load circuit. Ensure that the call and reset signals are connected to the correct terminals.
Use the appropriate wire gauge for the load current. The wire gauge should be large enough to carry the maximum load current without overheating. For example, a 5A load requires 18AWG wire, while a 16A load requires 14AWG wire.
Secure the wires to the terminal block using the appropriate method (screw terminals, spring-clamp terminals) to ensure a tight connection. Loose connections can cause arcing, overheating, and damage to the relay.
Provide electrical isolation between the control circuit and the load circuit, as specified by the relay’s datasheet. This may require using shielded cables or optocouplers.

6.1.3 Polarity (for DC Coils)

For Call&Reset Relays with DC coils, ensure that the polarity of the call and reset signals is correct. Reversing the polarity may prevent the relay from activating or resetting properly. The relay’s datasheet will indicate the correct polarity for the coil terminals (typically marked with “+” and “-”).

6.2 Maintenance Guidelines

Regular maintenance of Call&Reset Relays helps to extend their service life and ensure reliable operation. Below are the key maintenance tasks:

6.2.1 Visual Inspection

Perform a visual inspection of the relay regularly (monthly or quarterly) to check for signs of damage, such as: Cracked or damaged housingLoose or corroded terminalsBurned or discolored contacts (for electromechanical relays)Damaged or frayed wiresLED status indicator not working (for electronic relays)

If any damage is detected, replace the relay immediately to prevent system failure.

6.2.2 Cleaning

Keep the relay clean and free from dust and debris, which can cause overheating and poor connections. Use a soft brush or compressed air to remove dust from the relay’s housing and terminals. Do not use water or cleaning solvents, as they can damage the relay’s electronic components.

6.2.3 Contact Inspection (Electromechanical Relays)

For electromechanical Call&Reset Relays, inspect the contacts regularly to check for wear, arcing, or oxidation. If the contacts are burned or corroded, they may need to be cleaned or replaced. Use a contact cleaner (specifically designed for electrical contacts) to clean the contacts, and ensure that the contacts are properly aligned.

6.2.4 Coil Inspection

Check the coil’s resistance regularly using a multimeter to ensure that it is within the range specified in the datasheet. If the coil resistance is too high or too low, the coil may be damaged, and the relay should be replaced.

6.2.5 Replacement

Replace the relay when it reaches the end of its service life (as specified in the datasheet) or if it fails any of the inspection or testing tasks. When replacing the relay, ensure that the new relay has the same technical parameters (coil voltage, contact rating, contact configuration) as the old one.

6.3 Troubleshooting Common Issues

If a Call&Reset Relay is not operating properly, use the following troubleshooting guide to identify and resolve the issue:

6.3.1 Relay Does Not Activate (No Call Response)

Possible causes and solutions: Call signal not applied: Check the call signal source (pushbutton, sensor, PLC) to ensure that it is generating a valid signal. Use a multimeter to measure the voltage at the call coil terminals—if no voltage is present, the signal source is faulty.Coil damaged: Measure the coil resistance using a multimeter. If the resistance is open (infinite) or shorted (zero), the coil is damaged—replace the relay.Wrong coil voltage: Ensure that the call signal voltage matches the relay’s coil voltage rating. If the voltage is too low, the relay will not activate; if it is too high, the coil will be damaged.Mechanical jamming (electromechanical relays): Check the armature and latch for mechanical jamming. If the armature is stuck, gently tap the relay to release it, or replace the relay if jamming persists.

6.3.2 Relay Does Not Reset (Stays Activated)

Possible causes and solutions:Reset signal not applied: Check the reset signal source to ensure that it is generating a valid signal. Measure the voltage at the reset coil terminals—if no voltage is present, the signal source is faulty.Reset coil damaged: Measure the reset coil resistance using a multimeter. If the resistance is open or shorted, the coil is damaged—replace the relay.Mechanical latch stuck (electromechanical relays): The mechanical latch may be stuck, preventing the armature from returning to its default position. Gently tap the relay to release the latch, or replace the relay.Flip-flop malfunction (electronic relays): The latching circuit (flip-flop) may be malfunctioning. Replace the electronic relay.

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Post time: Jan-29-2026

Call&Reset Relay: Principles, Classifications, Applications and Future Trends