1756-M02AS | Allen-Bradley Servo Motion Modules

The Allen-Bradley 1756-M02AS is a 2-axis analog servo interface module designed for ControlLogix programmable automation controllers. Installed into any open chassis slot, it drives servo actuators and drives using ±10 VDC velocity or torque references while providing position feedback via Synchronous Serial Interface (SSI) absolute encoders. The module facilitates closed-loop motion routines, dynamic velocity profiles, and coordinated multiaxis interpolation directly within the Logix 5000 environment.

SSI Position Feedback and Multi-Option Servo Control

The module provides two independent channels of SSI absolute position feedback, accepting differential RS-422 signal inputs for precise position tracking without incremental homing routines. Position loop closure, velocity feedforward, and PID gain calculations are handled directly on the hardware board, delivering sub-millisecond loop updates to external drive amplifiers. Integrated inputs support 24 VDC home switches and 5 VDC or 24 VDC registration sensors for axis latching and event execution.

Electrical Isolation and Power Distribution

Operating power is drawn directly from the ControlLogix chassis backplane bus, utilizing 700 mA at 5.1 VDC and 2.5 mA at 24 VDC, with a total power dissipation of 5.5 Watts. Channel-to-backplane electrical isolation is rated for 30V continuous, preventing ground loops and protecting controller logic circuits from field-side interference. Field wiring connects via a 36-pin Removable Terminal Block (1756-TBCH or 1756-TBS6H) equipped with keying tabs to enforce correct physical alignment.

Technical Specifications

Removable Terminal Block Installation

Before installing the 36-pin terminal block onto the module header, wire field connections using 22 to 14 AWG conductors rated for at least 105 °C. Align the wedge-shaped keying tabs on the RTB to match the module keying slots to prevent miswiring. Insert the wired assembly into the front connector until the retaining latches click into place.

Frequently Asked Questions

Q: What position feedback devices are supported by the 1756-M02AS? A: The 1756-M02AS specifically supports absolute encoders with Synchronous Serial Interface (SSI) RS-422 differential outputs. For quadrature incremental encoders, the 1756-M02AE module must be used instead.

Q: Can registration inputs on the 1756-M02AS accept current sinking sensors?A: No, registration inputs must be wired for current sourcing operation because the registration input common (IN_COM) is shared with the module's 24 VDC inputs.