Siemens G85139 - Manual (Page 19)

4. OPERATING MODES English
© Siemens plc 1997 G85139-H1750-U049-B
19 26/09/97
4.6 Closed Loop Control
4.6.1 General Description
The MICROMASTER provides a PI control function for closed loop control (see Figure 11). PI control is ideal
for temperature or pressure control, or other applications where the controlled variable changes slowly or
where transient errors are not critical. This control loop is not suitable for use in systems where fast response
times are required.
Note: The closed loop function is not designed for speed control, but can be used for this provided that fast
response times are not required.
When closed loop PI control is enabled (P201 = 002), all setpoints are calibrated between zero and 100%, i.e.
a setpoint of 50.0 = 50%. This allows general purpose control of any process variable that is actuated by
motor speed and for which a suitable transducer is available.
Setpoint
Scaling
P211, P212
Feedback
Sample
Rate
P205
Low Pass
Filter
P206
P
P202
I
P203, P207
Acceleration/
Deceleration
Ramp
P002, P003
Motor
M
Process
e.g. fan
Transducer
P208
+
–
P201 = 000
Feedback
(e.g. duct pressure)
P201 = 002
Closed Loop Mode Disabled
Closed Loop Mode Enabled
P210
Feedback
Monitor
Figure 11: Closed Loop Control
4.6.2 Hardware Setup
Connect the outputs from the external feedback transducer to control terminals 3 and 4. This analogue input
accepts a 0/2 - 10 V signal, has 10-bit resolution and permits a differential (floating) voltage. Ensure that the
values of parameters P023 and P024 are set to 000 and that P006 is set to 000 or 002.
15 V dc power for the feedback transducer can be supplied from terminals 8 and 9 on the control block.
4.6.3 Parameter Settings
Closed loop control cannot be used unless P201 is first set to 002. Most of the parameters associated with
closed loop control are shown in Figure 11. Other parameters which are also associated with closed loop
control are as follows:
P001 (value = 007)
P061 (value = 012 or 013)
P210
P220
Descriptions of all closed loop control parameters are provided in section 5. For further detailed information
about PI operation refer to the Siemens DA 64 Catalogue.