Sequencer 01 through Sequencer 16 - Johnson Controls - Metasys - LIT-12011147 - Software Application - Controller Configuration Tool - 15.0

Controller Tool Help

Brand
Johnson Controls
Metasys
Product name
Controller Configuration Tool
Document type
User Guide
Document number
LIT-12011147
Version
15.0
Revision date
2022-11-18
Language
English

The Sequencer module behaves the same as the Sequencer block in the Metasys NAE.

The Sequencer module provides a Control System with multiple stage sequence control. This module controls discrete systems where the relative capacities of the stages are known. This module uses relative capacities to determine which outputs to turn on or off. The method is based on the split-range control concept, and it allows a single feedback controller, such as a PID, to control multiple stages. This module should be operated continuously (that is, do not place this module in a hybrid activity). The activity disables all modules associated with a specific state when that state is not active. There is no user interface to this disable/enable behavior.

The sequencer module establishes a means of sequentially activating 1 to X stages of individual devices. The sequencer control algorithm performs the following main functions:

  • Handles transitions between stage combinations using make and break limits. See Configuration Details for details on make and break limits. See Staging Up and Staging Down for details on staging up and staging down.

  • Provides equipment protection by enforcing minimum on and off times. See Minimum On and Minimum Off for details.

    Note: The user can defeat this protection by interacting directly with the output points.
  • Provides Interstage on and off delays. See Interstage Timing for details.

  • Allows instant deactivation of all outputs based on an Instant Shutdown input. See Instant Shutdown for details.

  • Provides intelligent rotation of the start and stop order of the outputs based on the rank and the device status. The sequencer module also allows the user to force a rotation to occur immediately. See Lead Rotation for details on lead rotation.

  • Provides the relationship between outputs (for example, runtime, number of starts). Devices with a lower rank value start before devices with a higher rank value, and devices with a higher rank value are deactivated before devices with a lower rank value. If the rank values are equal, the output with the lowest device number is activated first, and the output with the highest device number is deactivated first.

  • Indicates whether the device is active, inactive, or disabled. Active devices are first on the sequence order, inactive devices are second, and disabled devices are last. This function provides a simple method to determine the next device to start or stop.

  • Provides for a First On, Last Off operation (default sequence order).

  • Provides intelligent actions when a device is enabled or disabled. See Device Enable for details.

Configuration Details

The number of actively managed stages depends on the Number of Outputs and the operating mode (normal or proactive).

When the sequencer is operating in a proactive mode, the lead output of the sequencer module is activated continuously when the sequencer is enabled and Instant Shutdown is False. This scenario causes the actively managed stages to be one less than the Number of Outputs. When it is not in a proactive mode, the lead output of the sequencer module is activated when the input exceeds the first make limit. In this case, the actively managed stages are equal to the Number of Outputs.

The sequencer maintains one make limit and one break limit for each of the output stages it must actively manage. When in Normal mode, the first make and break limits are the start and stop limits for stage 1. When in proactive mode, the first make limit and break limit are the start and stop limits for the second stage since the first stage is active continuously.

The input values at which the sequencer activates and deactivates each configured stage is contingent on the sets of make and break limits specified for the sequencer. You can configure the make and break limits.

If a change to the make or break limits would cause an output to change state, it changes state provided that the Interstage, minimum on and minimum off timing are satisfied.

If a timer prevents an output from starting or stopping, the module activates or deactivates the output when the timer expires.

Staging Up

A staging up process involves comparing the input value against each of the make limits defined for the sequencer module. When an input value equals or exceeds a make limit, when the Interstage On Delay is not active and when the next device to activate does not have an active Minimum Off Timer, the sequencer reacts by increasing the current stage. If more than one make limit is exceeded, the sequencer stages up one stage at a time with an Interstage On Delay between each stage. When an increase in the current stage occurs, the Interstage On Delay starts.

If an Interstage Off Delay is active when a make limit is exceeded, it does not prevent the stage up. When a stage up occurs, any active Interstage Off Delay is canceled.

Staging Down

A staging down process involves comparing the input value against each of the break limits defined for the sequencer module. When an input value is less than or equal to a break limit, when the Interstage Off Delay is not active, and when the next device to deactivate does not have an active Minimum On Timer, the sequencer decreases the current stage. If more than one break limit has been passed, the sequencer stages down one stage at a time with an Interstage Off Delay between each stage. When a decrease in the current stage occurs, the Interstage Off Delay starts.

If an Interstage On Delay is active when a break limit is exceeded and it does not prevent the stage down. When a stage down occurs, any active Interstage On Delay is canceled.

Minimum On and Off Timing

The outputs are all subject to minimum on and minimum off timers. The sequencer maintains individual timers for each output. These timers protect equipment from excessive wear due to short cycling. Timers are cleared if the sequencer is commanded to Rotate Now or the Rotate Now input transitions from False to True.

When an output is activated, it remains active for the Min On Time. This occurs even if the input to the sequencer indicates that it should stage down. If the output that needs to be deactivated has an active Minimum On Timer, the sequencer waits for that timer to expire before staging down and deactivating that device. Setting the Instant Shutdown input to True causes the Minimum On Timer to be ignored and all devices are immediately deactivated.

When an output is deactivated, it remains inactive for the Min Off Time. This occurs even if the sequencer decides to stage up. If the output that needs to be activated has an active Minimum Off Timer, the sequencer waits for that timer to expire before activating that output. At startup, the sequencer considers all minimum off timers to have been met. If the Instant Shutdown input is True, the minimum off timers are maintained for all outputs. If Instant Shutdown goes False and a device has its minimum off timer active, the sequencer waits for that timer to expire before staging up and activating that device.

When a Minimum On/Off timer expires, the module checks to see if a stage up or down is required (the input is currently greater than the next make limit or less than the appropriate break limit). If a change is required, the stage up or down occurs if the appropriate Interstage and Minimum On/Off timers have been met. If there are no pending changes, the module waits for the input to exceed a make limit or drop below a break limit to initiate a stage change.

Interstage Timing

Staged equipment requires some time to have an effect on the process variable. Delays between switching stages are used to ensure that the process variable has adequate time to sense the change from the capacity increase or decrease. Staging up and staging down are subject to Interstage on and off timers respectively. These timers are cleared and restarted if the sequencer is commanded to Rotate Now or the Rotate Now input transitions from False to True.

The Interstage On Delay Timer starts when the sequencer increases the current stage and must expire before the sequencer is allowed to increase the current stage again. The Interstage On Delay allows the process variable to respond to the increase in the system capacity before the control system continues to stage up.

If the input drops below a break limit while an Interstage On delay is active, the stage down occurs if the device to be deactivated has no active minimum on timer.

The Interstage Off Delay Timer starts when the sequencer decreases the current stage and must expire before the sequencer is allowed to decrease the current stage again. The Interstage Off Delay allows the process variable to respond to the decrease in the system capacity before the control system continues to stage down. Setting the Instant Shutdown input to True deactivates all outputs, ignoring the Interstage Off Delay.

If the input rises above a make limit while an Interstage Off delay is active, the stage up occurs if the device to be activated has no active minimum off timer.

When an Interstage timer expires, the module checks to see if a stage up or down is required (the input is currently greater than the next make limit or less than the appropriate break limit). If a change is required, the stage up or down occurs if all appropriate Minimum On/Off timers have been met. If there are no pending changes, the module waits for the input to exceed a make limit or drop below a break limit to initiate a stage change.

Instant Shutdown

When the Instant Shutdown input is True, all of the outputs are deactivated ignoring the Minimum On Timers and the Interstage Off Delay timer.

Lead Rotation

The following six events can cause the sequence order to change:

  • Device activation

  • Device deactivation

  • Enabling a device

  • Disabling a device

  • Change of a device’s rank value

  • Change in the Rotate Now input from False to True or receipt of a Rotate Now command.

The manner in which the outputs are scheduled for activation is based on a combination of three factors: the rank value defined for each device, whether or not the device is enabled, and whether or not the device is already active.

Dynamic Reordering

After any occurrence of the first five items (cited in the previous section), the sequence order is re-evaluated. The devices are placed into three distinct collections or categories:

  • Enabled and active

  • Enabled and not active

  • Disabled

Within each of the categories, the entries are arranged in ascending order beginning with the lowest ranked device and ending with the highest ranked device.

Note: If two or more devices are assigned equal rank values, they are ordered based on the device number.

The combination of the three categories is the overall sequence order with the enabled and active devices lowest in the list, followed by enabled and inactive devices and finally by disabled devices.

The dynamic reordering allows the current lead device to be changed without actually deactivating or activating any of the devices until a stage change is required. If an output is being deactivated, then the active output with the highest rank value is deactivated. If an output is being activated, then the inactive output with the lowest rank value is activated. After the device activates or deactivates, the groupings update.

Static Reordering

In the case that the sixth event occurs, the sequence order is reevaluated. This allows you to make an immediate change to the devices that are running.

Note: Static Reordering disregards all Interstage and Minimum On/Off Timers.

The devices are placed into two distinct collections or categories:

  • Enabled

  • Disabled

Within each of the categories, the entries are arranged in ascending order beginning with the lowest ranked device and ending with the highest ranked device.

Note: If two or more devices are assigned equal rank values, they are ordered based on the device number.

This method does not take into account the current status of the output (active or inactive). The combination of the two categories is the overall sequence order with the enabled devices lowest in the list.

When the reordering is complete, the sequencer module immediately switches the state of its outputs to match the new sequence order and Current Stage. This may result in currently active devices stopping and inactive devices starting. For devices that change state, any current Minimum On or Minimum Off timers are cleared and appropriate timers are started.)

Default Sequencing Order

At creation, the default sequence order matches the device numbering. The default value for Device X Rank is zero, so the sequencer module defaults to the device numbering for the sequence.

Device Enable

The sequencer module only activates those devices that are enabled. When an active device is disabled, it is immediately deactivated (disregarding minimum on timers) and the next available (enabled and inactivate) device is activated in its place if no timers are active.

When a device is enabled, the sequencer module reevaluates the sequence order. The sequencer continues to consider this device inactive when it becomes enabled. When a change is required by the make and break limits, the appropriate device is started or stopped.

If some of the output devices are disabled, the sequencer may not be able to provide 100 percent capacity. In that case, the input may continue to wind-up to a max value of 100 percent. When the load drops and the input signal drops, the value of the input must drop to the break limit associated with the last stage that is currently enabled before actually deactivating any outputs.

When a Device X Enable changes to false and the associated Device X Out is turned off, a minimum off timer is started.

You cannot view or modify the modules in this group’s logic.