Description

The Allen-Bradley 1336-CT-SP1A​ (catalogued as 1336-CT-SP1A, sometimes shown as 1336CTSP1A) is a factory-option DC current transducer / current-sensing printed circuit board designed for installation in the option-card slot of Rockwell Automation Allen-Bradley PowerFlex 1336 and 1336 PLUS II adjustable-frequency AC drives. Its purpose is to sense DC-link or motor-phase current via an internal Hall-effect or shunt-based transducer circuit and feed a conditioned, isolated representation of that current back to the drive’s digital signal processor (DSP) for enhanced vector-control torque regulation, accurate electronic overload protection, and optional external current monitoring. In drives equipped for closed-loop flux-vector control the Allen-Bradley 1336-CT-SP1A​ supplies the high-resolution current feedback necessary for tight speed / torque regulation at low RPM — a requirement that the drive’s basic V/Hz current-limit algorithm cannot meet alone.The Allen-Bradley 1336-CT-SP1A​ is a plug-in module — it slides into the dedicated option slot on the drive powerboard, requires no external power wiring (draws from the drive’s internal low-voltage supply), and is recognized automatically by the drive firmware when the appropriate parameter is set to enable the option. It may also provide a scaled analog output (typically 0–10 VDC or proportional to RMS motor current, depending on drive firmware version) that can be routed to an external analog input card for remote current trending or SCADA monitoring.

Application Scenarios

A paper-converting line running a 75 HP PowerFlex 1336 PLUS II drive on a center-winder had difficulty maintaining constant web tension during acceleration and deceleration because the drive was operating in open-loop V/Hz mode with only calculated (not measured) motor current. The winding tension exhibited ±8 % variation, causing splices to occasionally break. After installing the Allen-Bradley 1336-CT-SP1A​ current transducer option card and re-configuring the drive for closed-loop flux-vector mode (with parameter “Option Card Present = Yes” and “Control Mode = Flux Vector”), the drive began using real measured DC current feedback from the Allen-Bradley 1336-CT-SP1A​ to modulate torque output. Post-retrofit tension variation dropped to ±1.5 %, splice-break incidents fell by 90 %, and the line could now maintain tension down to 0.3 Hz (near-zero speed holding torque) — something impossible with inferred current alone. The plant maintenance lead noted that adding the Allen-Bradley 1336-CT-SP1A​ “turned a good drive into a precision servo-grade controller without changing the motor or power wiring.” This illustrates how the Allen-Bradley 1336-CT-SP1A​ transforms a standard VFD into a capable closed-loop vector drive by providing the missing current-feedback element.

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