Fisher 3620J Single-Acting Electro-Pneumatic Positioner with 4-20 mA DC Signal and Corrosion Resistant Design

Product Overview

The Fisher 3620J is a single-acting electro-pneumatic valve positioner designed for diaphragm or piston rotary actuators. It combines a 3610J pneumatic positioner with a 3622 electro-pneumatic converter. The converter receives a 4-20 mA DC signal and produces a proportional pneumatic output (0.2 to 1.0 bar / 3 to 15 psig) that drives the positioner stage.

The 3620J mounts integrally to the actuator housing. Action can be switched between direct and reverse in the field without extra parts. Zero, span, and crossover adjustments are accessible with a screwdriver after removing the cover. A small adjustable loop gain lets users fine-tune dynamic response for each actuator size and application.

The positioner provides accurate, fast-responding operation and withstands vibrations found in most plant environments. Supply pressure changes have minimal effect on operation. The case, components, and gasket materials are selected for harsh environments, with low copper aluminum alloy die castings for corrosion resistance. Bleed air purges internal parts and the actuator housing for additional protection.

Technical Specifications

Application Industry

The Fisher 3620J is used in chemical and petrochemical processing, power generation, water and wastewater treatment, and general industrial process control. It suits older pneumatic control loops and applications where reliable rotary valve positioning is required. The positioner mounts integrally to the actuator housing for a compact installation.

Common Problems

• No output signal with input present: Check for clogged nozzle. Clean the nozzle. Check air supply pressure.

• Slow or abnormal output pressure: Check supply pressure is within specification. Check the pneumatic amplifier and nozzle/flapper assembly.

• Linear response poor: Check the zero spring adjustment. Check the range adjustment mechanism position.

• Positioner does not respond: Verify supply pressure and pneumatic connections. Check that the converter is receiving the 4-20 mA signal.

• Air leakage: Check O-rings, gaskets, and diaphragm for wear. Replace as needed.

Replacement Models

The Fisher 3620J is a mature electro-pneumatic positioner platform. For modern digital communication and advanced diagnostics, the Fisher DVC6200 or DVC2000 digital valve controllers are the current-generation alternatives. For legacy installations, the 3620J serves as a direct replacement for the 3610J pneumatic positioner when electrical input is required. The 3620JP adds a position transmitter, and the 3620JPR adds remote mount capability. For cross-vendor alternatives, verify actuator mounting, travel range, and input signal compatibility before ordering.