Siemens SIMATIC ET 200SP Manual page 80

Modes and Functions
3.11 Function: Current control
● Low limit (S7 analog value): The manipulated value is always restricted to a high limit and
low limit. The "Low limit" parameter assigns the low limit in S7 analog format, relative to
the reference value of the current. A value higher or equal to 27648 is not allowed. The
Low limit value must be lower than the High limit.
Low limit example:
– The reference current is set to 1000 mA which should be the load current measured
– If the low limit is 100, this means the minimum current the controller will drive is
– If the controller calculates a control value below 0.36%, it will drive 0.36% and never
● Gain: The proportional gain parameter assigns the amplification factor for the P part of
the PID algorithm.
● TI (s): The integration time parameter determines the time interval of the integral action. If
TI is smaller than the controller cycle time, TI will be set internally to the controller cycle
time.
● TD (s): The derivative time parameter determines the time interval of the derivative
action. If TD is smaller than the controller cycle time, TI will be set internally to the
controller cycle time.
● TM_LAG (s): Time lag of the derivative action. The algorithm of the D-action contains a
delay of TM_LAG. If TM_LAG is smaller than half the controller cycle time, TI will be set
internally to half the controller cycle time.
Set point control
Your program controls the target value of the output current by setting the control interface
field OUTPUT_VALUE. The output format is selected in the parametrization record (see
parameter "output format"). For example, if the output format "per 100" is selected, writing
the value 60 in OUTPUT_VALUE means the target current value is 60% of the reference
current value (see parameter "reference value current").
Limit reached flags
The limit reached flags are available in the feedback interface.
QLMN_HLM: "1" means the manipulated value is at the high limit.
QLMN_LLM: "1" means the manipulated value is at the low limit.
For more information about the PID control parameters, refer to the CONT_C instruction
topic in TIA portal online help.
80
with 100% duty cycle.
100/27648 * 1000 mA = 3.6 mA that is equivalent to a duty cycle of 0.36%.
go lower than that value.
Technology module TM Pulse 2x24V (6ES7138‑6DB00‑0BB1)
Manual, 09/2015, A5E35061186-AA