PID - Analogue Regulation

INPUTS :
- VALIDATION : function validation input. The function remains
inactive for as long as this input is not activated. VALIDATION is implicitly
active if it is not connected.
- VALID_PRESET_VALUE : when active, this input validates the
PRESET_VALUE input. Otherwise, the "preset value" in parameters is used.
- PRESET_VALUE : byte input for external preset value. This
input is only taken into account when the VALID_PRESET_VALUE input is active.
- CURRENT_VALUE : Analogue input for the process value. In PID
or Discrete mode, this input is read every cycles define in window Parameters .
OUTPUTS :
- OUTPUT : analogue output varying between 0 and 255. In digital
mode, this OUTPUT is a trigger to the CURRENT_VALUE input. In PID mode, it is
the OUTPUT of a proportional integral derivative control which has modifiable
parameters.
- ALARM : the alarm is optional ; where it is validated
parameters, the user has the choice between an absolute alarm, i.e. independent
of any change to the preset value, and a relative alarm, which is dependent on
the preset value :
Absolute Alarm : the user configures a value. When the
value measured exceeds this value, the ALARM output switches to logic state
1.
Relative Alarm : the user configures a difference. When
the value measured is outside the range "preset value minus
difference/preset value plus difference", the ALARM output switches to logic
state 1. The values of the limits defining the range are recalculated each
time the preset value is changed.
- CURRENT_PRESET_VALUE : Analogue output for the preset
value in used. This output may take on the value of the PRESET_VALUE input when
VALID_PRESET_VALUE is active or take on the "preset value" in parameter when
VALID_PRESET_VALUE is inactive or not connected.
PARAMETERS :
- Type of Regulation : Discrete or PI, depending on the
regulation mode selected. By default : Discrete.
- Action : In hot mode, the OUTPUT must have an important value
to reach the required level (preset value) which is above the process
temperature measured. This is the default mode for controlling systems
such as radiators. In Cold mode, the logic of the OUTPUT is reversed. The
longer the OUTPUT is activated, the lower the temperature received as feedback
becomes. This is the mode used for controlling systems such as refrigerators.
The parameter must be defined according to the type of system controlled.
Incorrect configuration leads to a divergence in the temperature.
- Preset Value : this parameter defines the preset value when
the VALID_PRESET_VALUE input is inactive or not connected.
- Alarm Function : a check box to activate/deactivate the
"alarm" function. When active, it provides access to the alarm configuration
particulars, i.e. its type (Absolute, relative), a threshold temperature for an
absolute alarm or a temperature range for a relative alarm. The full breadth of
the range is twice the difference, since the difference is applied both above
and below the preset value, forming a band within which the relative alarm
will not be triggered. The Inhibition value defines the time delay within which
no alarm is taken into account. This counter starts running when a rising edge
occurs on the validation input. When the time delay comes to an end, the
alarms cease to be ignored.
There are two possible regulation
modes :
- PID: configurable control algorithm. The OUTPUT is an analogue
control value varying between 0 and 255.
- Digital: identical operation to a trigger whose upper limit is equal
to the setpoint + BP/2 % of the setpoint and lower limit is equal to the
setpoint - BP/2 % of the setpoint. If CURRENT_VALUE > upper limit, the
control output is set to 0; if CURRENT_VALUE < lower limit, the control
output is set to 255.
ATTENTION :
- In these two modes, the proportional action is define by a
proportional band that's means for low PRESET_VALUE ( near zero ), precision
will be very bad. It's advise to use PRESET_VALUE to the upper and lower limits
(-32768..0) and (0..32768), but on keeping a margin able to absorb the
depassements of the PRESET_VALUE.