Hach sc1000 - Manual (Page 104)

102
Advanced Operations
6.3.3.7 Function set to PWM CONTROL/PID CONTROL working mode
PWM CONTROL/PID CONTROL
SET FUNCTION
Default value: LINEAR
The 2nd SET FUNCTION menu sets the PWM signal status.
LINEAR Signal is linearly dependent on the process value.
PID CONTROL Signal works as a PID controller.
SET TRANSFER
Default value: 0%
Sets a substitute PWM ratio 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 has got an on/off ratio as set in the menu MANUAL OUTPUT.
MANUAL OUTPUT
(0%
– 100%)
Indicates the current on/off ratio.
Additionally the on/off ratio can be set (condition: SET MODE is set to MANUAL). Note that this
ratio cannot exceed a value beyond the values set in the MINIMUM and MAXIMUM menus.
PHASE
Default value: DIRECT
Reverses the leading sign of the control deviation for the PID controller.
MINIMUM
(0%
– 100%)
Default value: 0%
Sets the minimum PWM ratio.
MAXIMUM
(0%
– 100%)
Default value: 100%
Sets the maximum PWM.
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 PWM on/off ratio output signal. This band is determined as set point +/- dead zone. The
dead zone stabilizes the PID controlled system which have a tendency to oscillate.
PERIOD (0 – 600 s)
Default value: 5 seconds
Sets the cycle duration of the PWM output signal.
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 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.