Configuration
3.13
The PID implementation algorithm is:
)dPV/dt Td dt e1/Tr (e Kp MV
Where:
e(t) = PV-SP (direct) SP-PV (reverse)
SP = Setpoint
PV = Process Variable (Pressure, Level, Flow, etc.)
Kp = Proportional Gain
Tr = Integration Time
Td = Derivative Time
MV = Manipulated Variable (output)
The three configuration groups below are pertinent to the PID controller:
SAFETY LIMITS - this group enables the configuration of: Safety Output, Output Rate and Output
Lower and Upper Limits.
The Safety Output defines the value of the output in the case of equipment failure.
Output Rate is the maximum variation Rate allowed for the output, expressed in %/s.
The Lower and Upper Limits define the output range.
TUNING - this group enables the PID tuning to be performed. The following parameters may be
adjusted: Kp, Tr and Td.
Parameter Kp is the proportional gain (not the proportional band) that controls the PID proportional
action. It may be adjusted from 0 to 100.
Parameter Tr is the integral time that controls the PID integral action. It may be adjusted from 0 to
999 minutes per repetition.
Parameter Td is the derivative time controlling the PID derivative action. It may be adjusted from 0
to 999 seconds.
NOTE
All these parameters accept zero as input. Such value simply nullifies the corresponding PID control
actions.
OPERATION MODES - this group enables the configuration of: Control Action, Setpoint Tracking
and Power On.
The Control Action Mode enables the selection of the desired output action: direct or reverse. In
direct action, a PV increase causes an output increase; in reverse action, a PV increase causes an
output decrease.
When the Setpoint Tracking mode is enabled, it is possible for the Setpoint to follow the PV while in
Manual Control. Thus, when control passes to Auto, the Setpoint value will be that of the last PV
prior to the switching.
When the PID is enabled, the Power On mode allows the adjustment of the mode in which the PID
controls shall return after a power failure: Manual mode, Automatic mode or the last mode prior to
the power failure.
TABLE – If the table option is selected, the MV output will follow a curve according to the values
typed in the LD301’s characterization table. The points can freely be configured as percentage
values. For a better linearization, it is recommendable that the points are the closest possible, in the
less linear regions of the curve. The LD301 has an internal variable to enable and disable the
characterization table of the MV output of the PID.
Equipment Configuration
The LD301 enables the configuration not only of its operational services, but of the instrument itself.
This group includes services related to: Input Filter, Burnout, Addressing, Display Indication, Writing
Protection and Passwords.
INPUT FILTER - The Input Filter, also referenced to as damping, is a first class digital filter
implemented by the firmware. User configurable from any value higher than zero seconds in addition
to intrinsic sensor response time (0.2 s) (via digital communication). The transmitter mechanical
damping is 0.2 seconds.
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