Burkert Type 8630 - Manual (Page 24)

22 - 8630
S
YSTEM
D
ESCRIPTION
On operation of the TOP Control Continuous as a process controller, the abovementioned position
control becomes a subordinate auxiliary control loop; the result is a cascade control. The process
controller in the main loop of the TOP Control Continuous has a PID function. The setpoint specified is
the process setpoint (SP) and it is compared with the process variable to be controlled. The actual
position (XPOS) of the pneumatic actuator is measured via the position sensing system. The controller
compares this actual value of the position with the setpoint (CMD) , which can be specified as a
standard signal. If a control difference (Xd1) exists, a pulse-width modulated voltage signal is sent to the
positioning system as the correcting variable. With single-acting actuators, if the difference is positive,
the pressurizing valve is driven via output B1. If it is negative, the exhaust valve is driven via output E1.
In this way, the position of the actuator is altered until the control difference is zero. Z2 represents a
disturbance.
* Operation as a process controller (option)
Process
Transmitter
Process
setpoint Process controller
Valve
opening
CMD
PV
Xd2 SP
Z2
Process variable
Positioning
system Soleno-
id valves Continuous
Valve
Position sensor
Positioner
Valve
opening
XPOS
Xd1
B1
E1
P
K
Z1
Process
control
loop
Example of process control:
TOP Control Continuous with sensor
Position control loop