Digital electro-pneumatic positioners offer adaptive control and low air consumption
January 16, 2008
TZIDC digital positioners suit any valve or actuator application. One device controls the position of linear or rotary actuators as well as single- or double-acting pneumatic cylinders. Available in explosion-proof, general-purpose, and intrinsically safe models, the TZIDC positioners accept 4-20 mA and digital input signals, and offer option modules for both digital and analog position feedback. A local operator interface makes all setup functions accessible from an on-board keypad, while a local LCD shows percent valve position, setpoint deviation, actual mA value, and temperature. The ABB TZIDC positioner incorporates a unique Adaptive Control mode that “learns” the behavior of the associated valve, actuator, and positioner combination while controlling the process. In this way the TZIDC will determine the optimum positioner control parameters for the application. It will optimize the positioner control performance by automatically adjusting its control parameters as the dynamic conditions of the valve changes with time. When at steady state (no signal change), the TZIDC positioner bleeds only 0.015 scfm, independent of supply pressure. A small difference in scfm air consumption per positioner multiplied by all the positioners in a plant over time can result in significant saving in air and energy consumption. Within the TZIDC positioner, when valve position matches the instrument signal, an internal 3/3-way valve closes in its center position to minimize the air consumption.