Siemens SIMATIC S7-300 Manual page 253

Offset compensation
The analog modules in the positioning control loop (D/A converter of the
FM354 and closed-loop controller module of the drive) cause a zero error
because of operating-voltage and component tolerances. The result is that at
an internal digital rotational-speed specification of zero in the FM 354, the
drive motor will already be running undesirably. As a rule, drive controllers
have adjustment capabilities for balancing. But by setting a voltage offset via
MD44 the analog system can be balanced at startup from the FM side.
44
For calculation of the offset value, see Section 7.3.2, Drive interface.
Direction alignment
MD19 allows you to align the direction by defining an assignment between
the voltage sign of the manipulated signal and the axis movement.
19.1
Voltage ramp
A ramp–shaped voltage rise/drop can be defined in MD45 for the voltage
output to the drive when the position controller is inactive. This serves to
limit acceleration and thus power for the drive controller, and is preferable to
setting options that may be available on the drive, since it has no adverse
effects on active position control.
The voltage ramp is active in the following situations:
45
D/A converter Output of analog voltage setpoint
FM 354 Servo Drive Positioning Module
MD Designation
Offset compensation
MD Designation
Direction adjustment
Continuously in Control mode
Deceleration on cancelation of the drive enable [AF] (see Section 9.1.1)
Deceleration on transition of CPU from RUN to STOP
Deceleration on error response "Everything Off" (see Sections 11.1, Tab.
11-4 and 11-5)
MD Designation
Voltage ramp
Description of Functions
Value/Meaning
–1,000...+1,000
Value/Meaning
1 = invert analog value
Value/Meaning
0...10,000,000
Unit
(mV)
Unit
–
Unit
(mV/s)
9-77