Our plant's pneumatic actuators are few but varied — mainly Fisher, ABB and Siemens. A pneumatic actuator generally comprises an air filter, cylinder, solenoid valve, electronic switch and travel-switch gear. In principle a 4–20 mA input passes through the valve controller, converting current to pressure and, comparing with position feedback, controlling air supply to set the valve opening.
Fisher pneumatic valves carry the DVC6000 series digital valve controller — a communicating, microprocessor-based electro-pneumatic instrument. Beyond converting current to pneumatic output pressure, the Model 275 HART Communicator gives easy access to information vital to process operation.
Fisher controllers are configured with the Model 275 HART Communicator, so mastering it matters. The 275 comprises a numeric keypad, an LCD (8 lines × 21 characters, showing instrument data when connected), action keys and function keys. The keypad selects menus and enters data; action keys are on/off, direction keys and the hot key.
The communicator works offline (unconnected) or online (connected). On power-up it self-tests then searches for compatible devices; finding none it shows "HART No Device Found", then the main menu.
Four choices appear: Offline, Online, Frequency Device and Utility. On finding a HART device the Online menu appears. The F1–F4 function keys beneath the LCD select functions named by dynamic labels; in any menu the label states the key's role there. Functions include: HELP — information on displayed options; SEND — send entered data to the instrument; BACK — previous menu; HOME — Online menu; EXIT — return to where you requested a read-only parameter; ABORT — cancel input and return, values unchanged; OK — next menu or instruction screen; ENTER — send your selection or tag a number for sending (SEND then appears as a function option); DEL — delete the letter at the cursor; ESC — cancel input, values unchanged; SAVE — store to memory or the data stack.
To configure and calibrate, Protection must be None and Instrument Mode Out of Service.
To remove protection:
To view Instrument Mode, press the hot key and choose Instrument Mode; if it is not Out of Service, select Out of Service and press ENTER (F4).
Two basic setup methods exist via Online → Setup & Diag → Basic Setup: Auto Setup (recommended) — automatically selects configuration parameters for the specified actuator type and size; Manual Setup — enter values for 1. Instrument Mode; 2. Control Mode; 3. Pressure & Actuator; 4. Tuning & Calib.
For pressure and actuator parameters choose Pressure & Actuator and enter: Pressure Unit, Max Supply Pressure, Actuator Type, Feedback Connection, Tvl Sensor Motion, Valve Style, Zero Control Signal.
To tune, set travel cut-off low point and relay, or auto-calibrate travel, choose Tuning & Calib, then: Tuning Set, Tvl Cutoff Low, Relay Adjust, Auto Calib Travel.
After valve maintenance the actuator travel must be recalibrated. Before travel calibration, check the pneumatic relay adjustment (1-1-1-3 or 1-4-8): choose Relay Adjust and follow the prompts, then replace the controller cover. Travel calibration offers manual and automatic modes; automatic is recommended as manual is complex and difficult.
From the Online menu choose Basic Setup, Auto Setup and Auto Calib Travel (keys 1-1-1-4), or under Setup & Diag choose Calibrate, Auto Calib Travel (1-4-2), and follow the prompts.
With Feedback Connection Direct-Standard, auto-calibration interacts with the user for a more precise crossover (reference) point adjustment; other feedback connections need no interaction — start at step 5.
