Beckhoff EL2535 EtherCAT PWM Current Terminal

The Beckhoff EL2535 is a 2-channel pulse width current terminal for the EtherCAT system. It is specially designed for the precise control of single and double-coil proportional valves as well as proportional solenoid valves. The terminal regulates the output current through pulse width modulation of the supply voltage and is electrically isolated from the E-bus. The current values from 0 to the maximum output current are specified by the automation device through a 16-bit value. With a PWM frequency of 30 kHz and output current up to ±1 A per channel, the EL2535 delivers the responsiveness and resolution required for demanding fluid control applications.

Technical Specifications

The EL2535 features 2 PWM outputs with push-pull output stages. Nominal voltage is 24 V DC with a tolerance of -15% to +20%. Maximum output current is ±1 A per channel, with a typical short-circuit current of less than 2 A. The terminal is suitable for inductive loads greater than 1 mH. PWM clock frequency is 30 kHz, and the duty cycle is programmable from 0% to 100% in current-controlled mode. Resolution is 10 bits. The terminal includes reverse voltage protection and overload/short-circuit protection on the output stages. Current consumption from the E-bus is typically 110 mA, and from the power contacts is typically 30 mA plus load. Bit width in the process image is 48 I/O bits: 2 × 16-bit data and 2 × 8-bit control/status. Electrical isolation of 500 V is provided between E-bus and field potential. The terminal also includes 2 digital 24 V inputs. Operating temperature range is 0°C to 55°C, with storage from -25°C to 85°C. Weight is approximately 50 g.

Key Features

• 2-channel PWM output with push-pull output stage

• ±1 A output current per channel at 24 V DC nominal voltage

• 30 kHz PWM clock frequency for high-resolution control

• Current-controlled PWM for precise valve positioning

• Suitable for inductive loads greater than 1 mH

• Overload and short-circuit protection on output stages

• 500 V electrical isolation (E-bus/field potential)

• 2 additional digital 24 V inputs

• LED status indicators for each channel

• 10-bit resolution with 16-bit value setting

Proportional Valve Control

The EL2535 is optimized for controlling proportional valves used in hydraulic and pneumatic systems. Applications include regulating the flow rate of liquids or gases, controlling cylinder position and velocity, and adjusting pressure in industrial processes. The current-controlled PWM output ensures that the valve spool position is proportional to the command signal, regardless of temperature-related changes in coil resistance. The 30 kHz PWM frequency is above the audible range, reducing acoustic noise from the valve. The push-pull output stage allows both sourcing and sinking of current, enabling control of valves that require bidirectional operation or for use with external current sensing resistors.

EtherCAT Integration

The EL2535 connects to the Beckhoff EtherCAT system via the E-bus interface. Configuration is performed in TwinCAT engineering environment, which automatically detects the terminal and assigns process data objects. The 16-bit current setpoint value is written to the output channel, and the terminal reports back the actual current and diagnostic status. The terminal also supports features such as distributed clocks for synchronized current updates, and a watchdog function that sets the output to a safe state upon loss of communication. The compact 12 mm wide housing allows dense installation on DIN rails, saving cabinet space.

Applications

Typical applications of the EL2535 include servo-hydraulic presses, injection molding machines, mobile machinery (excavators, loaders), test stands, packaging equipment, and precision dispensing systems. The terminal is also used in wind turbine pitch control, where proportional valves adjust blade angles, and in industrial furnaces for gas flow control. The combination of 30 kHz PWM and current regulation provides stable control even in the presence of fluctuating supply voltage or temperature variations.

Installation and Wiring

The EL2535 mounts on a 35 mm DIN rail conforming to EN 60715. Installation is achieved using the double slot and key connection system for side-by-side mounting. The terminal accepts solid conductors (0.08 to 2.5 mm²), flexible conductors (0.08 to 2.5 mm²), and ferrules (0.14 to 1.5 mm²) via spring actuation by screwdriver. Stripping length is 8 to 9 mm. The power contacts can carry up to 10 A total. Wiring for the PWM outputs should use shielded cables for applications requiring high noise immunity, particularly when long cable runs (exceeding 10 meters) are used. The two auxiliary digital inputs can be used for feedback from limit switches or status sensors.

Environmental and Compliance

The EL2535 is CE and UL approved. It conforms to EN 60068-2-6 for vibration resistance and EN 60068-2-27 for shock resistance. EMC immunity and emission conform to EN 61000-6-2 and EN 61000-6-4. Relative humidity tolerance is 95% without condensation. Protection rating is IP20; the terminal must be installed in a control cabinet or enclosure. The housing material is polycarbonate, and markings are applied using the BZxxxx labeling system.

Conclusion

The Beckhoff EL2535 EtherCAT PWM current terminal offers a compact, high-performance solution for precise control of proportional valves and solenoids in industrial automation. Its 30 kHz PWM, ±1 A output current, and current-controlled regulation provide the accuracy and speed required for demanding fluid power and motion control applications.