ABB TZIDC-200 Digital Positioner “Fail-safe” function
“Fail-safe” function
If the electrical supply power fails, the positioner output 1 is
depressurized, and the pneumatic actuator’s return spring
moves the valve to the defined safe position. In case of a
double-acting actuator the second output 2 is additionally pressurized.
Change from two to one column
“Fail-freeze” function
If the electrical supply power fails, the positioner output 1 (and
2. if applicable) is closed and the pneumatic actuator stops
(“freezes”) the valve in the current position. If the compressed
air supply power fails, the positioner depressurizes the actuator.
The air flow for pressurizing or depressurizing the actuator is
continuously adjusted. As a result, excellent control is
achieved. When reaching the setpoint, the 3/3-way valve is
closed in center position to minimize the air consumption.
Four different pneumatics versions are available: for single
acting or double-acting actuators, each with “fail-safe” or “fail freeze” function.