Siemens G85139 Manual De Usuario

4.  OPERATING MODES

English

© Siemens plc 1997

G85139-H1750-U049-B

19

26/09/97

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.

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

Feedback

Sample

Rate

Low Pass

Filter

Acceleration/

Deceleration

Ramp

Motor

Process

e.g. fan

Transducer

Closed Loop Mode Disabled

Closed Loop Mode Enabled

Feedback

Monitor

Figure 11:  Closed Loop Control

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.

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.