Technical data

Table Of Contents
System Software for S7-300/400 System and Standard Functions - Volume 2/2
A5E00739858-01
28-1
28 SFBs for Compact CPUs
28.1 Positioning With Analog Output Using SFB 44
"Analog"
Description
To control the positioning functions via the user program, use SFB ANALOG
(SFB 44).
A fixed assigned analog output controls the power stage with a voltage (voltage
signal) of ±10 V or with a current (current signal) of ±20 mA.
After the acceleration phase (RAM_UP) the drive approaches the target with
the speed (V
Setpoint).
At the braking point, that is calculated by the CPU, the deceleration
(RAMP_DN) up to the change-over point is initialized.
Once the change-over point is reached, run is continued with creep speed
(V
Creep).
The drive is switched off at the cut-off point.
The change-over point and the cut-off point are determined for every Step
Approach in the parameter values change-over difference and cut-off
difference you have specified. The change-over difference and cut-off
difference can be determined differently for the forward motion (in plus
direction) and for the reverse motion (in minus direction).
The run is completed (WORKING = FALSE) when the cut-off point is reached.
A new run can then be started.
The specified target is reached (POS_RCD = TRUE) when the actual position
value has reached the target range. If the actual position value drifts off without
a new run having been started the "Position reached" signal is not reset again.
When the change-over difference is smaller than the cut-off difference, the drive is
slowed down as of the braking point to the speed setpoint 0.
Basic Parameters:
Here we describe the SFB parameters which apply to all operating modes. The
parameters specific to the operating mode are described with the individual
operating modes.
Parameters: