Siemens SIMATIC ET 200SP Manual page 79

Setting up current control
In order to use the current control feature, the module must be parametrized correctly and
the set point (target value of the current) must to be controlled by the user program. In
addition, your program can also read the limit-reached flags.
PID parameters
The PID parameters can be set in TIA Portal device configuration or by your program writing
parametrization record (record 128) in the module. See the parametrization record
description (Page 138) for details.
● Current Control: "1" activates the PID controller. Limitations: Current control can only be
activated if the selected mode of operation is PWM and the high-speed output is
disabled.
All the following parameters have no effect, if current control is disabled.
● P_Sel, I_Sel, D_Sel: defines the PID control calculation. The proportional, integral, and
derivative parts can be enabled ("1") or disabled ("0") in the device configuration.
● Reference value current (mA): The reference value is used to define the maximum set
point and the high and low limits of the controlled current. Typically, the maximum current
can be measured in PWM mode with current control disabled and a duty cycle set
to 100%. The value measured can be set as a reference for the current control. The
maximum value is 4000 mA for single channel operation (parallel channel connection
enabled) and 2000 mA per channel for dual channel operation (parallel connection
disabled).
● Dead band width (μA): A dead band is applied to the output current deviation from the set
point current. The "Dead band width" is half of the size of the dead band. The dead band
is symmetrical: For example, if the dead band width = 1500 μA, then the dead band is
from -1500 μA to +1500 μA .
● High limit (S7 analog value): The manipulated value is always restricted to a high limit
and low limit. The "High limit" parameter assigns the high limit in S7 analog format,
relative to the reference value current. A value higher or equal than 27648 means
100% of the reference value current. The High limit value must be higher than the Low
limit.
High limit example:
– The reference current is set to 1000 mA which should be the load current measured
– If the high limit is 20000, this means the maximum current the controller will drive is
– If the controller calculates a control value higher than 72.34%, it will drive 72.34% and
Technology module TM Pulse 2x24V (6ES7138‑6DB00‑0BB1)
Manual, 09/2015, A5E35061186-AA
with 100% duty cycle.
20000/27648 * 1000 mA = 723.4 mA that is equivalent to a duty cycle of 72.34%.
never go higher than that value.
Modes and Functions
3.11 Function: Current control
79