The following table describes the attributes used by the MSC XX (where XX is 01 through 12) modules.
|
Name |
Description |
Default Value |
|---|---|---|
|
Active Stage Count |
Specifies the number of discrete devices under control that are in an on state. This output is equal to the total number of ON devices and is used for diagnostic purposes. |
|
|
Actual Period |
Specifies the actual instantaneous PMAC period of execution, measured as the actual time between successive periodic executions of the PMAC algorithm. |
Display Units: Seconds |
|
Capacity List |
Contains a list of the possible capacities based on the Device Capacity input. |
|
|
Control Band |
Contains the user-specified variation band of the controlled variable. Multistage Controller controls the pulse train output. The variation of the pulse train then causes the variation of the Process Variable to be equal to or smaller than the specified value.
Note: The minimum achievable Control Band is not zero, but is dependent on the system process time constant, process gain, minimum on/off times, and the number of stages. Multistage Controller may not be able to achieve the Control Band you set.
|
10 °C, 16 °F |
|
Deadzone |
Contains a value calculated from the Staging Hysteresis and the smallest Device X Capacity. Deadzone = Staging Hysteresis * smallest Device X Capacity. |
|
|
Desired Outputs |
Represents the preferred state of all Device X Out at this instant. If this is different from the actual state of the outputs, it is due to a minimum on or minimum off timer. |
|
|
Device Capacity |
Represents the relative capacity of each device. This value is used in establishing the order by which the devices are activated. These numbers can represent the wattage of an electric heater, the tonnage of a chiller, and so on. All capacities entered must be based on the same units and all combinations of the capacities are used to create the Capacity List.
Note: The Capacity List is limited to 50 entries. To limit the Capacity List to a maximum of 50, the user may need to round off the capacities to reduce the number of unique values (for example, use capacity of 5 for three devices with actual capacities of 4.6, 5.1, and 5.9).
|
1 (for all devices) |
|
Device First Of |
Specifies how many devices are in the group where this device is the first of the group. This device and the following (value - 1) devices are grouped together for control. The Device First Of attribute for the dependent devices of this group are ignored. |
1 (for all devices) |
|
Device Pulsable |
Represents the action allowed for the device. When this is False, the associated device is turned on or off only by the staging algorithm of this module. It is never selected as the Pulsed Device. If the value is True, then this device can be pulsed using the PMAC algorithm.
Note: If none of the devices are pulseable, the controlling PID should have its Adaptive Tuning input set to False.
Important: Using the MSC without a pulseable device may cause excessive cycling of the equipment.
|
True (for all devices) |
|
Device X Enable |
Establish the enable status of the devices. A value of False takes the associated device out of service. If a device is on when this is set to False, Device X Out is set off immediately, disregarding the minimum on timer. In Device X Enable, X is 1-12. |
True |
|
Device X Out |
Contains the output value for the corresponding device. In Device X Out, X is 1-12. |
Set Name: Off/On |
|
Device X Runtime |
Represent the ranking of each device. This value is used with the Device Capacity in establishing the order by which the devices are activated. In Device X Runtime, X is 1-12. |
0.0 |
|
Input |
Represents the required capacity from 0 to 100% of available capacity. This signal typically is fed from an upstream controller (for example, PID or a user defined algorithm). |
0.0% |
|
Instant Shutdown |
Forces all Device X Out to False when it is True. When it is False, the module monitors the input and sequences the devices. When this value transitions from False to True, all of the devices are deactivated instantly (ignoring any minimum on timers). |
False |
|
Invert Stage |
Indicates the action of devices within a group as specified in Device First Of. If this input is True, when the first device of a group is turned on, all the devices are turned on and the second and subsequent devices of the group are turned off sequentially as the load increases. If this input is False, when the first device of the group is turned on, the remaining devices of the group turn on sequentially as the load increases. |
False |
|
Max Capacity Fraction |
Contains the ratio of the largest enabled Device Capacity to the sum of all Device Capacity. |
|
|
Min Off Time |
Minimum time that a Device X Out must remain off before it can be reactivated to an on state (following deactivation). |
120 Seconds |
|
Min On Time |
Minimum time interval that a Device X Out must remain on before it can be deactivated to an off state (following activation). |
240 Seconds |
|
Min Percent Request |
Minimum output signal at Percent Request when any output is desired to be on. |
1.0% |
|
Min Period |
Defines the shortest period that can be executed. |
1 Second |
|
Number of Devices |
Number of devices controlled by this Multistage Controller. |
|
|
Off Pulse |
Specifies the width of the current off pulse of the Pulsed Device in seconds. |
Display Units: Seconds |
|
On Capacity |
Specifies the capacity of the on outputs in units of the Device Capacity. |
|
|
On Pulse |
Specifies the width of the current on pulse of the Pulsed Device in seconds. |
Display Units: Seconds |
|
Percent Capacity Enabled |
Indicates the percentage of the total capacity represented by the currently enabled devices’ capacities. |
|
|
Percent Request |
Indicates when the Multistage Controller requires the fan to be on. The value of this request depends on the property Percent Request Mode. |
|
|
Percent Request Mode |
Indicates the method used to control the output Percent Request. |
Demand Set Name: Percent Request Mode Enum Set |
|
PMAC Period |
Specifies the execution period of the PMAC algorithm of this module. If set to a value less than the Min Period property, the period requested for execution is limited to the Min Period. |
24 Seconds |
|
Process Time Constant |
Dominant time constant of the process being controlled. |
720 Seconds |
|
Process Variable |
Value from the area that is being controlled. It typically originates at a sensor and, after some signal processing, passes to the Multistage Controller module. |
0 °C, 0 °F |
|
Pulsed Device |
Current device that the PMAC algorithm controls at this capacity step. |
|
|
Requested Capacity |
Capacity requested by the Input in units of the Device Capacity. |
|
|
Rotate Now |
Retains a value of True until it is written back to False. (This attribute is rising edge activated.) Writing this attribute to True causes an immediate update (disregarding Min On Time and Min Off Time) of the active devices based on the current runtimes. All timers are cleared and the minimum on (for devices that transition to on) and minimum off (for devices that transition to off) timers begin counting from zero. |
False |
|
Staging Hysteresis |
Determines the Multistage Controller’s deadzone size (Deadzone divided by two is the amount the Input must be greater than a capacity switch point to increase the capacity. The Input must be less than a capacity switch point by this amount to decrease the capacity. The capacity list determines the capacity switch points. See Deadzone.) |
1.0% |
|
Timer Status |
Represents the status of any timers associated with all Device X Out at this instant. If the element corresponding to a specific Device X Out is True, then a minimum on or minimum off timer is active. If the element is False, then no timers are active. |
|
|
Vernier |
Contains an analog output of 0 to 100 that indicates the percentage of the currently pulsed device necessary to meet the required capacity. |
Display Units: % |