Pid Tuning Explanations - red lion T16 Manual

TIME PROPORTIONAL PID CONTROL
In Time Proportional applications, the output power is converted into
output On time using the Cycle Time. For example, with a four second
cycle time and 75% power, the output will be on for three seconds (4 ×
0.75) and off for one second.
The cycle time should be no greater than 1/10 of the natural period of
oscillation for the process. The natural period is the time it takes for one
complete oscillation when the process is in a continuously oscillating
state.
LINEAR PID CONTROL
In Linear PID Control applications, the Analog Output Assignment
is set to % Output Power, . The Analog Low Scaling,
:(:) "&
to 0.0 and the Analog High Scaling,
Output will then be proportional to the PID calculated % output power for
Heat or Cooling per the Control Action
10 VDC (scaled 0 to 100%) and 75% power, the analog output will be 7.5
VDC.

PID TUNING EXPLANATIONS

AUTO-TUNE
Auto-Tune is a user-initiated function that allows the controller to
automatically determine the Proportional Band, Integral Time, Derivative Time,
Digital Filter, Control Output Dampening Time, and Relative Gain (Heat/Cool)
values based upon the process characteristics. The Auto-Tune operation cycles
the controlling output(s) at a control point three-quarters of the distance between
the present process value and the setpoint. The nature of these oscillations
determines the settings for the controller's parameters.
Prior to initiating Auto-Tune, it is important that the controller and system be
first tested. (This can be accomplished in On/Off Control or Manual Control
Mode.) If there is a wiring, system or controller problem, Auto-Tune may give
incorrect tuning or may never finish. Auto-Tune may be initiated at start-up, from
setpoint or at any other process point. However, ensure normal process
conditions (example: minimize unusual external load disturbances) as they will
have an effect on the PID calculations.
Start Auto-Tune
Below are the parameters and factory settings that affect Auto-
Tune. If these setting are acceptable then Auto-Tune can be
started just by performing two steps. If changes are needed, then
they must be made before starting Auto-Tune.
DISPLAY PARAMETER
tYpE
Input Type
FLtr
Digital Filtering
On/Off Control
CHYS
Hysteresis
tcod
Auto-Tune Code
db-2
Deadband
tUnE
Auto-Tune Access
1. Enter the Setpoint value in the Display Loop.
2. Initiate Auto-Tune by changing Auto-Tune Start
the Hidden Loop.
Auto-Tune Progress
The controller will oscillate the controlling output(s) for four cycles. The
bottom display will flash the cycle phase number. Parameter viewing is
permitted during Auto-Tune. The time to complete the Auto-Tune cycles is
process dependent. The controller should automatically stop Auto-Tune and
store the calculated values when the four cycles are complete. If the controller
remains in Auto-Tune unusually long, there may be a process problem. Auto-
Tune may be stopped by entering ("
, is set
:(#"
:(*1 , is set to 100.0. The Analog
"&:4 . For example, with 0 VDC to
FACTORY
MODULE
SETTING
tc-A
T16
1-IN
Curr
P16
1 1-IN
2
T16
2-OP
0. 2
P16
[0] 2-OP
[0] 5-O2
[HidE] 3-LC
to in
,%(' ?')
in Auto-Tune Start ,%(' .
MANUAL CONTROL MODE
In Manual Control Mode, the controller operates as an open loop
system (does not use the setpoint and process feedback). The user
adjusts the percentage of power through the % Power display to control
the power for Output O1. When Alarm 2 is configured for Cooling (O2),
Manual operation provides 0 to 100% power to O1 (heating) and -100 to
0% power to O2 (Cooling). The Low and High Output Power limits are
ignored when the controller is in Manual.
MODE TRANSFER
When transferring the controller mode between Automatic and
Manual, the controlling outputs remain constant, exercising true
"bumpless" transfer. When transferring from Manual to Automatic, the
power initially remains steady, but Integral Action corrects (if necessary)
the closed loop power demand at a rate proportional to the Integral Time.
AUTOMATIC CONTROL MODE
In Automatic Control Mode, the percentage of output power is
automatically determined by PID or On/Off calculations based on the
setpoint and process feedback. For this reason, PID Control and On/Off
Control always imply Automatic Control Mode.
AUTO-TUNE CODE FIGURE
AUTO-TUNE OPERATION
(REVERSE ACTING)
23