ABB TZIDC-200 Digital Positioner Pneumatics
Pneumatics
An I/P module with subsequent pneumatic amplifier is used to
control the pneumatic actuator. The well-proven I/P module
proportionally converts the permanent electrical setpoint signal
from the CPU into a pneumatic signal used to adjust a 3/3 way valve.
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.
“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.