Hach sc1000 - Manual (Page 107)

105
Advanced Operations
6.3.3.9 Function set to FREQ. Control/PID CONTROL mode
FREQ. Control /PID CONTROL
SET FUNCTION
Default value: LINEAR
There are two SET FUNCTION menus.
First menu: Selects the basic function of the relay.
Second menu: Defines whether the output frequency signal is depending linear to the process
value or the output frequency signal is working as a PID controller.
LINEAR Signal is linearly dependent on the process value.
PID CONTROL Signal works as a PID controller.
SET TRANSFER
Default value: 0 seconds
Sets a substitute output frequency when some error conditions are detected in the selected
source or if the source is missing.
SET MODE Default value: AUTOMATIC
AUTOMATIC The relay output works as a PID controller
MANUAL The relay output frequency has a cycle duration which is set in the MANUAL OUTPUT menu.
MANUAL OUTPUT
Indicates the current cycle duration of the output frequency.
Additionally the cycle duration can be set (condition: SET MODE=MANUAL).
PHASE
Default value: DIRECT
With this menu the leading sign of the control deviation for the PID controller can be reversed.
SET POINT
Default value: 10
Sets the process value which is controlled by the PID controller.
DEAD ZONE
Default value: 1
The dead zone is a band around the set point. In this band the PID controller does not change
the output frequency. This band is determined as set point +/- dead zone. The dead zone
stabilizes the PID controlled system which have a tendency to oscillate.
HIGH ALARM
Default value: 1 second
Sets the maximum cycle duration which can be set by the PID controller.
LOW ALARM
Default value: 10 seconds
Sets the minimum cycle duration which can be set by the PID controller.
PROPORTIONAL
Default value: 1
Sets the proportional part of the PID controller.
The proportional part of the controller generates an output signal which is linearly dependent to
the control deviation. The proportional part reacts on any changes at the input but starts to
oscillate easily if the value is set to high. The proportional part cannot completely compensate
disturbances.
INTEGRAL
Default value: 15 minutes
Sets the integration part of the PID controller.
The integration part of the controller generates an output signal. The output signal increases
linearly if the control deviation is constant. The integration part responds slower than the
proportional part and can completely compensate disturbances. The higher the integration part,
the slower it responds. If the integration part is set to low, it starts to oscillate.
DERIVATIVE
Default value: 5 minutes
Sets the derivative part of the PID controller.
The derivative part of the PID controller generates an output signal which depends on the control
deviation changes. The faster the control deviation changes, the higher the output signal gets.
The derivative part creates an output signal as long as the control deviation changes. If the
control deviation is constant, no signal is created.
The derivative part is able to smoothen the oscillation caused by the proportional part. The
derivative part allows the proportional part to be set higher and the controller responds faster.
If there is no knowledge about the controlled process behavior, it is recommended to set this part
to “0”, because this part tends to oscillate strongly.