Future Design MCT-MC 4.3, Руководство пользователя

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MCT-MC
4.3
Device Settings - 101 - FDC MCT-MC
9.1 Tuning
The loop Tuning screen allows for manual and automatic tuning of the MC control loops. Tuning parameters
should only be manually adjusted by skilled users familiar with proportional control. Improper settings can result
in control loop instability and equipment damage. The loop automatic tune function is the recommended method
of loop tuning. If the control response achieved after performing an auto tune does not provide the desired
control response, then minor adjustment of the tuning parameters may be done manually to obtain the desired
response.
The available tuning parameters are dependent upon the loop configuration. If programmed for heat or cool
only control, then the available parameters will be PB (proportional band), TI (integral time period) and TD
(derivative time period). If the loop is configured for heat/cool operation then two additional parameters for
Cooling PB (cooling proportional band) and Dead Band (heat/cool dead band) will be provided.
The tune screen also provides a live real time chart for monitoring the control response of the control loop while
adjusting tuning parameters. The chart is fixed at a 10 minute time period and updates once per second.
Pressing the set point display field directly above the real time chart allows the user to adjust the loop set point
without having to leave the tuning screen in order to observe the control response.
Pressing the
A/M button allows the user to activate/deactivate the loop manual output mode. When the loop is
in manual mode, the indicator on the button will be illuminated. To adjust the loop percentage of output, touch
the loop output display field to display the numeric entry keypad.
Pressing the
AT button allows the user to activate/deactivate the loop auto tuning feature. When auto tune is
active, the indicator on the button will be illuminated. In addition, the process value of the loop on the Loop
view screen will flash while auto tune is active. This allows the user to activate auto tune and then return to the
main Loop view screen to observe system operation while being informed of the loop auto tune status.
9.1.1 Heat or Cool only P (or PD) Control
When a loop is programmed for heat or cool only control, it is possible to set the integral time to zero in order
to eliminate reset action. A “PB Offset” field will then be shown for entering a manual reset value to correct for
the control offset that will occur once the loop has stabilized. The offset entry is measured in percent with a
range of 0-100%.
Once the process has stabilized, if the process value is lower than the set point by 5° for example, and 20.0 is
used for the proportional band, that is equal to an offset of 25%. Thus, the PB offset would be increased by
25% to compensate for the set point offset in the process. Note that automatic tune is disabled for P or PD
control. In order to perform an auto tune, the integral time would have to be set to a value greater than zero.
P or PD control is not precise for processes with changing load conditions and will require frequent adjustments
of the offset. The PID control mode should be used because it automatically does this.