Future Design MCTB 4.3, Руководство пользователя

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MCTB
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set between two and five, the PID set entries are then written to the loop control according to the activation set
point and current process value.
The
PID Set Activation Set Point is the process value above which the PID set is utilized. PID sets two
through five have an activation set point. PID set one is the default PID set, so an activation set point is not
utilized. Each PID set activation set point must be greater than the previous set point. Thus, as the process
value increases, the PID set utilized will increase.
For example, a temperature control loop having the Number of Active PID Sets at a value of three, will result in
the loop control using one of three PID sets based on the current temperature. The PID sets will switch
according to the activation set points entered for PID set two and PID set three. For this example, PID set two
will have an activation set point of 100 degrees and PID set three will have an activation set point of 200
degrees.
Starting with a loop control set point (SP) and process value (PV) of 70 degrees, the loop will use PID set one
as both SP and PV are below the activation set points for PID set one and PID set two. In order for the PID set
to change to PID set two, both the SP and PV have to rise above the 100 degree activation set point. If the
user were to then change the loop SP to 150, the loop continue operation using PID set 1. As the temperature
starts to rise, PID set two values will then be written to the loop control once the PV rises above 100 degrees.
The loop will then continue to use PID set two until the SP is changed to a value within another PID set range
and the PV also enters that same range. If the user then changes the SP to 200 which matches the activation
set point of PID set three, the loop will use PID set two until the PV rises above 200. If the PV does not reach
the 200 activation set point, the PID set will not be activated. This prevents PID sets from actively toggling back
and forth at the activation point and causing control instability. Once the PV reaches the 200 degree activation
point, the PID set would switch to set three. PID set three would then remain in use even if the PV were to drop
below 200. Only when both SP and PV are below 200 would the PID set switch back to set two.
During operation, should the set point change span multiple PID sets, the PID sets will be activated as the PV
enters each activation range. Continuing from the example above, if the set point is changed back to 70
degrees, it is then in the PID set one range. However, with the PV at 200 degrees, PID set 3 is active. As the
temperature starts to decrease and the PV falls below 200 degrees, this will then activate PID set two. The
loop will then operate under PID set two. As the temperature continues to fall and drops below the PID set two
activation set point of 100 degrees, the loop will then begin operating under PID set one.
NOTE: As different PID sets are activating, the tuning constants shown on the Tuning screen will change to
the active PID set. The tuning constants on the Tuning screen are the actual PID values used by the
loop control. Thus, at any time during operation, the user is able to view the values currently in use.
Changing any of the values on the tuning screen will result in the loop control using the new value,
but will not affect the PID set. The manually entered value will remain in use until another PID set is
activated when the corresponding activation set point is met.
9.2 Alarms
The alarm screen allows the user to edit the alarm set points and alarm messages that will be displayed on the
alarm screen should the alarm be activated.