Technology instructions
10.2 PID control
S7-1200 Programmable controller
618 System Manual, V4.2, 09/2016, A5E02486680-AK
An autotuning for a cascaded master controller must meet these requirements:
● Be commissioned from its inner slave to the first master.
● All slaves of the master have to be in “Automatic mode".
● The output of the master must be the setpoint for the slaves.
PID_Temp instruction will provide the following support for autotuning in the cascade:
● If you start autotuning for a master controller, the master checks to see if all slaves are in
“Automatic mode” and for the deactivation of the Replacement-Setpoint-functionality for
all slaves (“ReplacementSetpointOn” = FALSE). If you do not meet these conditions, you
cannot autotune the master. The master cancels the tuning, goes to “Inactive” mode" (if
“ActivateRecoverMode” = FALSE), or back to the mode stored in the “Mode” parameter (if
“ActivateRecoverMode” = TRUE). The master displays the error message 200000hex
("Error with master in the cascade. Slaves are not in automatic mode or have a substitute
setpoint enabled and are preventing tuning of the master.").
● When all slaves are in “Automatic mode”, the system sets the parameter
“AllSlaveAutomaticState” = TRUE. You can apply this parameter in your programs or
localize the cause of error 200000hex.
● When the "ReplacementSetpoint" is deactivated for all slaves, the system sets the
parameter “NoSlaveReplacementSetpoint” = TRUE. You can apply this parameter in their
programs or localize the cause of error 200000hex.
When the PID_Temp instruction commissioning dialog is used, you have further support for
cascade tuning (Page 642).
Operation modes and error handling
The PID_Temp controller does not allow switching of the operating mode by its master or
slaves. This means that a master inside the cascade stays in its current mode when a slave
raises an error. This is an advantage if two or more parallel slaves operate with this master
controller; an error in one chain does not shut down the parallel chain.
Similarly, a slave inside the cascade stays in its current operation mode, if its master has an
error. However, further operation of the slave then depends on the configuration of the
master because the slave’s setpoint is the master’s output. This means that if you configure
the master with “ActivateRecoverMode” = TRUE and an error occurs, the master outputs the
last valid or a substitute output value as setpoint for the slave. If you configure the master
with “ActivateRecoverMode” = FALSE, the master switchs to “Inactive mode" and sets all
outputs to "0.0" so that the slave uses "0.0" as its setpoint.
Because only the slave controllers have direct access to the actuators and these stay in their
operating mode in case of a master error, you can avoid damage to the process. For
example, for plastics processing devices, it is fatal for the slaves to stop working, shut down
the actuators, and allow the plastic to harden inside the device solely because the master
controller had an error.
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