Product Overview

The Schneider Electric SR2A101BD is a Zelio Logic compact smart relay for small-scale automation and electrical control applications. It operates on a 24 V DC supply and combines programmable logic, six digital inputs, four relay outputs, and an integrated display in one compact control device. The model does not include a real-time clock, making it suitable for applications where control logic and event sequencing are required without clock-based scheduling.

Unlike a conventional control relay, the SR2A101BD executes a user-defined program. It can process input signals, evaluate logical conditions, and switch output contacts according to the programmed sequence. This makes it useful for replacing groups of conventional relays and timers in relatively simple machines, utility equipment, and standalone control panels.

The six inputs accept compatible 24 V DC signals from push buttons, limit switches, proximity sensors, and other discrete field devices. The four relay outputs provide switching contacts for suitable control circuits. Within the permitted electrical ratings, these outputs can operate contactor coils, indicator lamps, interface relays, and other control loads.

For example, a small pumping station may use the SR2A101BD to respond to level switches, process start and stop commands, and control a pump contactor. The programmed logic can incorporate operating conditions and interlocks, while the output contacts provide the switching signals required by the external control circuit. The actual motor power circuit and its protective devices remain separate from the smart relay’s control functions.

The integrated display and navigation buttons allow operators and maintenance technicians to view information and interact with supported functions locally. The device can be programmed using Zelio Soft software, with ladder logic and function block diagram programming available for the applicable configuration. This makes it accessible for straightforward automation tasks without requiring a full PLC system for every application.

Program retention is another useful feature. The built-in EEPROM memory provides data backup for up to ten years under the specified reference conditions, helping preserve the stored program during a power interruption. This is particularly useful in standalone control panels where the application program must remain available after supply power is restored.

The SR2A101BD is intended for applications with a defined set of digital signals and relatively straightforward control sequences. Its six inputs and four relay outputs establish the available onboard I/O, so applications requiring numerous sensors, analog measurements, or extensive communication functions may need a different controller or an expanded automation arrangement.

Because the outputs are relay contacts, their electrical ratings and switching characteristics must be considered when selecting connected loads. Inductive loads, frequent switching, and high inrush currents can affect contact life. Where the controlled equipment requires greater switching capacity or a separate power circuit, appropriately rated contactors or interface relays should be used.

The absence of a real-time clock also influences application design. The SR2A101BD can execute programmed logic based on its inputs and internal program conditions, but it is not the appropriate choice when the application depends on a built-in clock for scheduled daily or weekly operations.

The Schneider SR2A101BD is therefore suited to compact automation tasks that need programmable control, local display access, 24 V DC operation, and four relay outputs without the complexity of a larger PLC installation.

Technical Specifications

Product Features

• Programmable control logic: Executes user-defined sequences for small machines and electrical control systems.
• Six digital inputs: Accepts compatible 24 V DC signals from switches, sensors, and operator controls.
• Four relay outputs: Provides switching contacts for compatible control loads.
• Integrated display: Allows local access to supported operating information and interface functions.
• Ladder logic and FBD programming: Supports two programming approaches for implementing control sequences.
• 24 V DC power supply: Fits control panels using a low-voltage DC control supply.
• EEPROM program retention: Preserves stored program data for up to ten years under the specified reference conditions.
• No real-time clock: Suits applications that do not require built-in calendar-based scheduling.
• DIN rail or screw mounting: Supports installation in suitable electrical enclosures.
• Compact standalone control: Combines basic logic processing and output switching in a single device.

Working Principle

The SR2A101BD operates by reading the electrical states of its six digital inputs, evaluating the programmed logic, and updating its four relay outputs according to the program.

24 V DC Supply → SR2A101BD → Program Execution → Relay Outputs → Control Loads

The input circuits receive signals from connected field devices. A push button, for example, may indicate an operator start request, while a limit switch reports the position of a moving component. The smart relay reads these input states and makes them available to the program for processing.

The program determines how the input conditions affect the outputs. A simple control sequence may require a start signal, a valid interlock condition, and the absence of a stop command before energizing an output. More complex sequences can combine multiple conditions, timers, counters, and internal logic functions supported by the device.

Ladder logic represents control relationships in a format familiar to technicians working with conventional relay circuits. Function block diagram programming represents the application as connected functional blocks. The appropriate method depends on the complexity of the task and the programmer’s preferred approach.

Once the program evaluates the required conditions, the controller updates the output states. The four relay outputs operate their contacts to switch compatible external control circuits. For example, an output may energize a contactor coil that controls a motor power circuit. The smart relay itself should not be treated as a substitute for the contactor, motor protection, or required safety devices.

The integrated display and navigation interface provide local access to supported device functions. During commissioning, the technician can use the programming software and local interface to establish the required program and review the controller’s operating condition.

The SR2A101BD operates from a 24 V DC supply within its specified voltage limits. The power supply must be suitable for the controller and any connected control-circuit requirements. Voltage drop, grounding arrangements, and electrical interference should be considered when field devices are distributed across a machine.

Its EEPROM memory retains the stored program during loss of supply under the specified conditions. When power returns, the controller can resume operation according to its configured behavior and the states of the connected equipment. The external machine circuit must still be designed so that restoration of power does not create an unintended or hazardous restart.

Because the model does not include a real-time clock, time-based scheduling tied to the calendar is not an onboard function. Applications that require scheduled start times or day-of-week logic should use a controller with the necessary clock functionality or a suitable external timing arrangement.

During troubleshooting, input indications, program conditions, output states, and the external wiring should be checked separately. If an output does not operate, the cause may be an unmet logic condition, an incorrect program assignment, a missing supply, or a fault in the external load circuit. Separating these checks helps identify the source of the problem without unnecessarily replacing the smart relay.

Through programmable input processing and relay-based output switching, the SR2A101BD provides a straightforward control solution for compatible small automation systems.

Role in the Industrial Control Architecture

The SR2A101BD acts as the local logic controller between field input devices and external control loads. It processes signals and executes the programmed sequence without requiring a separate PLC for every simple automation task.

Field Sensors and Operator Controls → SR2A101BD → Relay Outputs → Contactors and Control Loads

The SR2A101BD handles basic programmed control. Power switching, electrical protection, and safety-related functions must be implemented using equipment and circuit arrangements appropriate to the machine.

Industrial Applications

Installation and Maintenance

1. Verify the model reference: Confirm that the installed device is SR2A101BD and that its I/O arrangement suits the intended application.
2. Prepare the control enclosure: Provide suitable mounting, wiring access, and environmental conditions for the IP20 device.
3. Install the smart relay: Use a compatible 35 mm DIN rail or the supported screw-fixing arrangement.
4. Check the DC supply: Verify that the control supply remains within the specified 19.2–30 V DC range.
5. Identify the input channels: Label each field signal and verify its voltage, polarity, and wiring arrangement.
6. Connect the relay outputs: Wire each output according to the terminal diagram and the electrical requirements of the connected load.
7. Review load switching requirements: Check contact voltage, current, inrush, and inductive-load characteristics before connecting external equipment.
8. Develop the control program: Implement the required logic using supported ladder or function block diagram programming.
9. Test interlocks and operating sequences: Verify that start conditions, stop commands, position signals, and other programmed conditions produce the intended response.
10. Check power-restoration behavior: Confirm that the machine responds safely when supply power is interrupted and restored.
11. Inspect the external control circuits: Check contactors, interface relays, protective devices, terminal tightness, and connected field devices.
12. Maintain program records: Keep a copy of the approved program, I/O assignments, wiring diagrams, and commissioning settings.

If the smart relay does not respond as expected, check the DC supply, input signals, program logic, and output wiring in sequence. If an output command is present but the controlled equipment does not operate, inspect the external load circuit and switching equipment before concluding that the smart relay has failed.

Related Components

Recommended Related Models

Key Advantages

• Combines programmable logic, six digital inputs, and four relay outputs in one device.
• Operates from a 24 V DC control supply.
• Supports ladder logic and function block diagram programming.
• Provides an integrated display for local interaction.
• Retains program data in EEPROM memory under the specified conditions.
• Supports DIN rail or screw mounting in suitable control enclosures.
• Suits small automation systems that do not require a larger PLC architecture.

Technical FAQs

Can the SR2A101BD control a motor directly?

The smart relay provides four relay outputs for control circuits; it is not a motor power controller. For a typical motor application, a relay output commands a suitably rated contactor, while the motor power circuit uses appropriate protective devices. The contactor and protection arrangement must be selected for the motor and its operating conditions.

What is the effect of having no real-time clock?

The SR2A101BD can execute programmed logic based on its inputs and supported internal functions, but it does not provide a built-in real-time clock for calendar-based scheduling. Applications that require daily schedules or day-of-week control need a suitable external timing arrangement or a smart relay model with clock functionality.

How should the four relay outputs be used when controlling inductive loads?

The connected load must remain within the output contact ratings. Inductive loads such as contactor coils can generate switching transients and accelerate contact wear, so appropriate suppression should be used where required. For loads with higher current or inrush demands, an interface relay or suitably rated contactor may be necessary.

What happens to the stored program after a power interruption?

The built-in EEPROM memory provides program data backup for up to ten years at the specified reference temperature of 25°C. After power is restored, operation depends on the configured behavior and the states of the connected circuits. The external machine should be designed to prevent an unsafe restart following a supply interruption.