User`s manual

94 Chapter 7 535 User's Manual
Applications
around the setpoint. If the Response Time is set too long, response to an
off-setpoint condition will be sluggish. It is generally better to use too long
a response time than too short.
Self Tuning with Multiple Sets of PID
For both Pretune and Adaptive Tune, the tuned set of PID is that which is ac-
tive upon initiation of the tuning function.
The controller cannot trip to other PID sets (based on trip point or the digital
input contact) until Adaptive Tuning is disabled. However, if the PID set is tied
to the corresponding local setpoint, the active PID set values will change with
the local setpoint.
Each PID set has 5 parameters that control its function—proportional band,
reset, rate, manual reset (or loadline), and trip point. For each set (2 thru 8),
these values have to be manually set.
1. Press MENU to access the TUNING menu.
2. Set values for parameters 1 thru 20 (these include the first PID set).
3. Press MENU to access these parameters for each additional PID set (2
through 8): PROP. BND, RESET, RATE, MAN. RST. and TRIP.
Self Tune with Time Proportioning Outputs
When using either the Pretune or the Adaptive Tune with a time proportioning
output, use as short of a cycle time as possible within the constraint of
maintaining a reasonable life on relays, contacts or heating elements.
Self Tune with Control Valves
In many systems utilizing a control valve, the point at which the control valve
begins to stroke does not coincide with 0% output, and the point at which it
completes its stroke doesn’t coincide with 100%. The parameters LOW OUT
and HIGH OUT in the CONTROL menu specify the limits on the output. Set
these limits to correspond with the starting and stopping point of the valve’s
stroke. This prevents a form of “windup” and thus provides the adaptive control
algorithm with the most accurate information.
For example, in manual the control output was slowly increased and it was noted
that the control valve started to stroke at 18% and at 91% it completed its stroke.
In this case LOW OUT should be set at 18% and HIGH OUT at 91%.
Note that when output limits are used, the full output range from -5 to 105% is
available in manual control.
N. RAMP-TO-SETPOINT
The 535 contains a ramp-to-setpoint function that may be used at the user’s
discretion. This function is especially useful in processes where the rate-of-
change of the setpoint must be limited.
When the ramping function is activated, the controller internally establishes a
series of setpoints between the original setpoint and the new target setpoint.
These interim setpoints are referred to as the actual setpoint . Either setpoint
may be viewed by the user. When the setpoint is ramping, RAMPING will be
shown in the 3rd display when the actual (ramping) setpoint is displayed.