Product Overview

The Schneider Electric SR2B201B is a Zelio Logic compact smart relay for small industrial machines, building services, and standalone automation panels. It operates from a 24 V AC supply and provides 20 I/O points, comprising 12 discrete inputs and eight relay outputs. An integrated LCD display and real-time clock support local operation, programmable sequencing, and scheduled control without requiring a larger PLC for straightforward applications.

The SR2B201B is suitable for control systems in which several field signals must be processed and multiple devices operated according to defined conditions. Its inputs can receive compatible 24 V AC signals from push buttons, limit switches, auxiliary contacts, and other discrete field devices. The eight relay outputs provide switching contacts for compatible external control circuits, including contactor coils, interface relays, and indicator circuits.

A practical application is a small conveyor system with several position switches, manual start and stop commands, and multiple independently controlled sections. The SR2B201B can evaluate the sensor states, apply the programmed interlocks, and coordinate the output sequence. This replaces groups of conventional control relays and timers with a programmable arrangement that is easier to modify when the machine sequence changes.

The built-in real-time clock adds another useful capability. Lighting, ventilation, and utility equipment can be operated according to programmed schedules while still responding to manual commands and machine conditions. For example, a ventilation controller can enable operation during designated periods and use additional input signals to determine whether the equipment is permitted to run.

The SR2B201B has eight relay outputs, twice the output count of the 12-I/O SR2B121B. This additional capacity is useful when a control panel contains several independent output circuits. However, the number of outputs alone does not determine how much equipment can be switched directly. Contact ratings, common-terminal current limits, load characteristics, and switching frequency remain important when assigning output channels.

Programming is supported through Zelio Soft, with ladder logic and function block diagram methods available for supported applications. Ladder logic is familiar to technicians who work with conventional relay circuits, while function block diagrams provide an alternative way to organize timing, counting, and other control functions. The integrated LCD and navigation buttons support local access to available device information and functions.

The controller’s EEPROM memory retains the stored program for up to ten years at the specified reference temperature of 25°C. This helps preserve the application during a supply interruption and simplifies program recovery during maintenance. Keeping a separate copy of the approved program remains useful when replacing a controller or restoring a machine configuration.

One important characteristic of the SR2B201B is its 24 V AC supply and input arrangement. It should not be treated as a 24 V DC smart relay simply because both voltage ratings use the same nominal number. Where field devices operate from a DC supply, their signals must be compatible with the controller’s input requirements or use an appropriate interface arrangement.

The SR2B201B is a practical option for small control panels that need 20 I/O points, relay-based output switching, an AC control supply, and clock functions. It is most appropriate for discrete automation tasks that do not require integrated analog measurement, advanced motion control, or extensive network communication.

Technical Specifications

Product Features

• 20 onboard I/O points: Combines 12 discrete inputs and eight relay outputs for multi-device control sequences.
• 24 V AC power supply: Fits control panels using a compatible AC control-power arrangement.
• Twelve discrete inputs: Processes operating commands, position signals, and equipment feedback.
• Eight relay outputs: Provides mechanical switching contacts for compatible AC or DC control circuits.
• Integrated LCD display: Supports local access to available device information and functions.
• Built-in real-time clock: Allows supported programs to incorporate scheduled operating periods.
• Ladder logic programming: Supports control sequences based on familiar relay-logic principles.
• Function block diagram programming: Provides an alternative way to organize supported logic operations.
• EEPROM program retention: Retains the stored application for up to ten years at 25°C.
• Flexible mounting arrangement: Supports 35 mm DIN rail installation or the specified screw-fixing method.
• Multiple output channels: Helps coordinate several independently controlled devices from one smart relay.

Working Principle

The SR2B201B reads the states of its 12 discrete inputs, evaluates the stored program, and operates its eight relay outputs according to the programmed conditions. Its real-time clock also supplies time information for supported scheduling functions.

24 V AC Supply → SR2B201B → Program Execution → Relay Outputs → External Control Circuits

The input circuits receive compatible 24 V AC signals from field devices. A push button may provide a start command, a limit switch may indicate the position of a moving component, and an auxiliary contact may report whether a contactor is energized. These signals become conditions within the control program.

The program determines how the input states affect machine operation. In a conveyor application, a start command may be accepted only when the required interlocks are satisfied. Additional logic can coordinate several conveyor sections, prevent conflicting output commands, and activate an alarm when a specified condition occurs.

Ladder logic represents these conditions through contacts, coils, and supported logic elements. Function block diagram programming uses connected functional blocks to organize the required operations. Both methods can implement suitable control sequences, with the choice depending on the programmer’s preferred approach and the complexity of the application.

When an output condition becomes true, the corresponding relay contacts change state and switch the connected external circuit. An output may energize a contactor coil, which then switches a motor power circuit. The SR2B201B performs the control function; motor switching, branch-circuit protection, and overload protection must be provided by appropriately selected external equipment.

The eight relay outputs allow the controller to operate more independent circuits than a four-output model. However, output assignment must account for the current through each contact and the applicable common-terminal limits. The total thermal current for all eight outputs is specified as 8 A, so this limit must be considered alongside the individual contact ratings.

The real-time clock supports programs that use scheduled operation. For example, a lighting panel can enable its control sequence during programmed periods while retaining manual commands and interlocks. The actual behavior depends on the program logic, clock settings, and the states of connected devices.

The SR2B201B does not provide analog input channels. A temperature transmitter, pressure transmitter, or other device producing a continuous measurement signal cannot be connected directly as though the controller had analog measurement capability. Applications requiring these signals need suitable conversion equipment or a controller with compatible analog inputs.

The integrated LCD provides local access to supported monitoring and device functions. Zelio Soft can be used to develop and transfer the program. During commissioning, technicians should verify the input states, clock settings, program conditions, and relay output responses against the intended machine sequence.

EEPROM memory retains the application program for up to ten years at 25°C. After power is restored, the machine’s behavior depends on the program configuration and external circuit states. The control system should be arranged to prevent unexpected or hazardous movement following a supply interruption.

When an output does not operate, the diagnosis should distinguish between an unmet logic condition, an inactive output, a wiring fault, and a problem in the external load circuit. Checking these stages separately helps locate the cause without replacing components unnecessarily.

Role in the Industrial Control Architecture

The SR2B201B acts as the local programmable controller between field input devices and external control circuits. It collects discrete signals, evaluates the application logic and supported clock functions, and switches its eight relay outputs.

AC Field Devices → SR2B201B → Relay Outputs → Contactors and Control Loads

The smart relay manages the programmed sequence, while external switching equipment handles the power loads. The final architecture must account for input voltage compatibility, output ratings, electrical protection, and the machine’s required safety functions.

Industrial Applications

Installation and Maintenance

1. Verify the model reference: Confirm that the installed device is SR2B201B and that its 20-I/O configuration meets the application requirements.
2. Prepare the control enclosure: Provide suitable mounting, wiring access, and environmental conditions for the controller.
3. Install the controller: Use a compatible 35 mm DIN rail or the specified screw-fixing arrangement.
4. Check the AC supply: Verify that the supply voltage remains within the specified 20.4–28.8 V AC range and that the frequency is compatible.
5. Identify the input channels: Label the 12 input circuits and confirm that the connected field signals meet the 24 V AC input requirements.
6. Wire the relay outputs: Follow the terminal diagram and observe the applicable contact and common-terminal current limits.
7. Review connected loads: Check voltage, current, inrush, and inductive characteristics before assigning loads to the relay outputs.
8. Develop the control program: Implement the required sequence using supported ladder logic or function block diagram programming.
9. Configure clock functions: Set the real-time clock and schedule parameters for applications that use time-dependent operation.
10. Test the input logic: Operate each field device and verify that the controller detects the expected input state.
11. Verify output and restart behavior: Test relay responses, external contactors, interlocks, scheduled operation, and power-restoration behavior.
12. Maintain program records: Keep the approved application, I/O assignments, clock settings, wiring diagrams, and commissioning results.

If an input is not detected, check the field signal, supply arrangement, and terminal wiring. If a relay output does not operate, inspect the program conditions and output state before checking the external load circuit. Isolate the relevant electrical supply before performing wiring or maintenance work.

Related Components

Recommended Related Models

Key Advantages

• Provides 12 discrete inputs and eight relay outputs in a 20-I/O configuration.
• Operates from a 24 V AC supply.
• Includes a real-time clock for supported scheduled operations.
• Provides an integrated LCD display for local interaction.
• Supports ladder logic and function block diagram programming.
• Retains the stored program in EEPROM under the specified conditions.
• Suits small automation systems with multiple discrete control circuits.

Technical FAQs

How does the SR2B201B differ from the SR2B201BD?

The SR2B201B uses a 24 V AC supply and accepts compatible 24 V AC discrete input signals. The SR2B201BD uses a 24 V DC supply and is intended for compatible DC input circuits. Both models provide 20 I/O points, eight relay outputs, a display, and a real-time clock, but their supply and input arrangements are different.

Can the eight relay outputs switch eight loads at their maximum individual current simultaneously?

The combined output arrangement must respect the specified total thermal-current limit of 8 A across all eight outputs, as well as the individual contact ratings and common-terminal limits. The maximum rating of one contact should not be interpreted as the permissible combined current for every output operating at once.

Can the SR2B201B be used to process a continuous temperature or pressure signal?

The SR2B201B has 12 discrete inputs and no analog input channels. A continuous temperature or pressure signal requires a suitable interface that converts the measurement into a compatible discrete condition, or a separate controller with the appropriate analog input capability.

What is the purpose of the real-time clock in the SR2B201B?

The real-time clock allows supported programs to use scheduled operations, such as switching lighting or ventilation circuits during designated periods. These schedules can be combined with input conditions and interlocks so that time-based operation remains coordinated with the machine’s operating requirements.