Global Sequencer - Johnson Controls - Metasys - LIT-12011147 - Software Application - Controller Configuration Tool - 15.0

The Global Sequencer module provides a Control System with multiple stage sequence control. This module uses make and break limits to determine which outputs to turn on or off.

The Global Sequencer module provides two optional outputs specifically targeted for compressors and chillers. The Solenoid Valve Out is used to support a pump down cycle before turning off the last stage. The Oil Pump Out provides a means to turn on a single oil pump that serves a group of compressors. In that case, the Oil Pump Out must turn on with the first compressor.

The Global Sequencer module can only exist within a Control Sequence or Control Activity within a Control Sequence. This module should be operated continuously (that is, do not place this module in a hybrid activity). The hybrid 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 devices using five sequencer staging modes: Step, Sequential, Equal Runtime, Equal Startup, and Binary Code. 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 inter-stage on and off delays. See Inter-Stage 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 runtime, the number of starts, 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. In Equal Runtime mode, the device with the lowest Device n Runtime is ranked lowest. If devices have equal runtime, their Device n Start Count is compared to determine which has the lowest rank. If there is still no lowest ranked device, the devices are ranked based on their Device Number. In Equal Startup mode, the device with the lowest Device n Start Count is ranked lowest. If devices have equal Device n Start Counts, their Device n Runtime is compared to determine which has the lowest rank. If there is still no lowest ranked device, the devices are ranked based on their Device Number.

• The Sequence Order attribute indicates the order that the devices start and stop in. It includes all devices, whether 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 intelligent actions when a device is enabled or disabled. See Device Enable for details.

Sets (Device Groupings) and Stages (Device n Outputs)

The device outputs or stages can be grouped into sets, each set having a definable number of stages. This option is applicable to chiller compressor control where the stages are connected to unloader solenoids. When this option is enabled, all stages within a set are switched on when the first stage of a set is switched on, and then the second and subsequent stages are switched off as the load increases. The behavior can be changed so that when first stage turns on, the second and subsequent stages stay off and are switched on as the load increases.

As the load decreases, the reverse operation occurs. A set only turns off its first stage when the second and subsequent stages are considered off.

When one of the rotation staging methods is chosen, only the runtime or number of starts for the first device in a set is used. Inputs that match the other devices in the set are ignored. When equal runtime within sets is true, the stages within a set use their runtime to determine which one starts first.

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 inter-stage, 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.

When the property Calculate Make Break Limits is False, the user manually sets the Make and Break Limit arrays. When the property is set to True, the user sets the Capacity array and the differential values. The Make and Break Limits are then calculated based on these values. The Make and Break Limits are recalculated whenever a change occurs in the sequence order.

Staging Details

The sequencer can perform Vernier Control in all modes except Binary Code providing a proportional signal between steps.

Step Mode

The output stages are controlled in sequence according to the last on, first off principle. For example, a three-stage sequencer controls the output stages in the following sequence examples. Example 1 shows three stages where each stage is a set. Example 2 shows stages within a set, with set 1 representing a compressor with two unloaders. In this case, the unloaders turn off to load the compressor.

Sequential Mode

The sets are controlled in sequence according to the first on, first off principle with a goal of equalizing runtime and start counts. Stages within a set are controlled to the last on, first off principle (like Step mode).

For example, a three-set sequencer controls the output sets in the following sequence: (0 = Off, 1 = On)

Equal Runtime

In Equal Runtime mode, the device with the lowest Device n Runtime is ranked lowest. If devices have equal runtime, their Device n Start Count is compared to determine which has the lowest rank. If there is still no lowest ranked device, the devices are ranked based on their Device Number.

The On time of the first output stage of each set is totalized. In case of an increase of load requiring the activation of a new set, the set with the lowest On time is switched on. In case of a decrease of load requiring the switching off of a stage in a set at full load, the set with the highest On time is switched off first. Stages within a set are controlled to the last on, first off principle (Step mode). For example, a three-set sequencer controls the output sets in the following sequence: (0 = Off, 1 = On)

When multiple Stages have the same runtime (such as, ON time), the Stage with the lowest number of starts is activated first. If a new Stage needs to be switched OFF, the Stage with the highest number of starts among those with greater runtime is switched OFF.

• Example 1: Three stages and each stage is a set. As the load increases, the set with a runtime of 40 hours starts first. As the load decreases, the set with a runtime of 110 hours stops first.

  Table 6. Increasing Load: 3 Sets, Each Set is One Stage (0=Off, 1=On)

  Runtime	Load (Percent)	0	33	66	100
  90 hours	Set 1/Stage 1	0	0	0	1
  40 hours	Set 2/Stage 2	0	1	1	1
  65 hours	Set 3/Stage 3	0	0	1	1

  Table 7. Decreasing Load: 3 Sets, Each Set is One Stage (0=Off, 1=On)

  Runtime	Load (Percent)	100	66	33	0
  95 hours	Set 1/Stage 1	1	1	1	0
  110 hours	Set 2/Stage 2	1	0	0	0
  99 hours	Set 3/Stage 3	1	1	0	0

• Example 2: Stages within a set, set 1 represents a compressor with two unloaders. The unloaders turn off to load the compressor. As the load increases, the set with a runtime of 40 hours starts first. As the load decreases, the set with a runtime of 110 hours stops first.

  Table 8. Increasing Load: Three Sets, First Set is One Stage (Stage 1), Sets Two and Three are a compressor with a loader (Stage 2, 3, 4, 5: Stage 1, 2, 4: 0=Off, 1=On; Stage 3, 5: 0=Load, 1=Unload)

  Runtime	Load (Percent)	0	40	50	60	80	100
  90 hours	Set 1/Stage 1	0	0	0	1	1	1
  90 hours	Set 2/Stage 4	0	0	0	1	0	0
  90 hours	Set 2/Stage 2	0	0	0	1	1	0
  40 hours	Set 3/Stage 5	0	1	1	1	1	1
  65 hours	Set 3/Stage 3	0	0	1	1	1	1

  Table 9. Decreasing Load: Three Sets, First Set is One Stage (Stage 1), Sets Two and Three are a compressor with a loader (Stage 2, 3, 4, 5: Stage 1, 2, 4: 0=Off, 1=On; Stage 3, 5: 0=Load, 1=Unload)

  Runtime	Load (Percent)	100	80	60	50	40	0
  95 hours	Set 1/Stage 1	1	1	1	1	1	0
  95 hours	Set 2/Stage 4	0	0	0	0	1	0
  95 hours	Set 2/Stage 2	0	0	0	1	1	0
  110 hours	Set 3/Stage 5	1	0	0	0	0	0
  99 hours	Set 3/Stage 3	1	1	0	0	0	0

Equal Startup

In Equal Startup mode, the device with the lowest Device n Start Count is ranked lowest. If devices have equal Device n Start Counts, their Device n Runtime is compared to determine which has the lowest rank. If there is still no lowest ranked device, the devices are ranked based on their Device Number.

For Equal Startup, the number of OFF to ON transitions, and the ON time of each Stage is totalized. In case of an increase of load requiring the activation of a new Stage, the Stage with the lowest Start-Up (for example, OFF to ON transitions) is switched ON.

In the case where multiple Stages have the same number of starts, the one with the lowest runtime (for example, ON time) is activated first. If a new Stage needs to be switched OFF, the Stage with the highest runtime among those with greater transition number is switched OFF.

• Example 1: Three stages and each stage is a set. As the load increases, the set with a number of starts of 40 starts first. As the load decreases, the set with a number of starts of 110 hours stops first.

  Table 10. Increasing Load: Three Sets, Each Set is One Stage (0=Off, 1=On)

  Number of Starts	Load (Percent)	0	33	66	100
  90 starts	Set 1/Stage 1	0	0	0	1
  40 starts	Set 2/Stage 2	0	1	1	1
  65 starts	Set 3/Stage 3	0	0	1	1

  Table 11. Decreasing Load: Three Sets, Each Set is One Stage (0=Off, 1=On)

  Number of Starts	Load (Percent)	100	66	33	0
  95 starts	Set 1/Stage 1	1	1	1	0
  110 starts	Set 2/Stage 2	1	0	0	0
  99 starts	Set 3/Stage 3	1	1	0	0

• Example 2: Stages within a set, set one represents a compressor with two unloaders. The unloaders turn off to load the compressor. As the load increases, the set with a number of starts of 40 starts first. As the load decreases, the set with a number of starts of 110 hours stops first.

  Table 12. Increasing Load: Three Sets, Each Set is One Stage (Stage 1, 4, 5: 0=Off, 1=On; Stage 2, 3: 0=Load, 1=Unload)

  Number of Starts	Load (Percent)	0	40	50	60	80	100
  90 starts	Set 1/Stage 1	0	0	0	1	1	1
  90 starts	Set 2/Stage 2	0	0	0	1	0	0
  90 starts	Set 3/Stage 3	0	0	0	1	1	0
  40 starts	Set 2/Stage 4	0	1	1	1	1	1
  65 starts	Set 3/Stage 5	0	0	1	1	1	1

  Table 13. Decreasing Load: Three Sets, Each Set is One Stage (Stage 1, 4, 5: 0=Off, 1=On; Stage 2, 3: 0=Load, 1=Unload)

  Number of starts	Load (Percent)	100	80	60	50	40	0
  95 starts	Set 1/Stage 1	1	1	1	1	1	0
  95 starts	Set 2/Stage 2	0	0	0	0	1	0
  95 starts	Set 3/Stage 3	0	0	0	1	1	0
  110 starts	Set 2/Stage 4	1	0	0	0	0	0
  99 starts	Set 3/Stage 5	1	1	0	0	0	0

Binary Code

The binary code sequencer always selects the appropriate stage combination for the requested output, with a stage delay between the changing of a stage combination. The sequencer does not step through successive combinations when a large change in requested output occurs. For example, in the following table, if the Input changes from 0 to 2, the sequencer immediately turns on the 2 kW stage.

The output stages must form one set and are controlled in sequence according to a binary code principle. For example, a three-stage sequencer controls the output stages in the following sequence.

Sequencer Control

The sequencer control is either proactive or retroactive. This is controlled by setting the Proactive property. When it is True, the sequencer operates proactively. When Proactive is False, the sequencer acts retroactively.

• Proactive = True

  The first stage selected by the sequencer is always On unless the Instant Shutdown input is True. The second stage is switched On when the first stage is at its load factor, the third stage when the second stage is at its load factor, and so on. This mode is normally required for equipment with its own modulating control, for example, centrifugal refrigeration compressors.

  Figure 1. Proactive Control
  

  

  
  

• Proactive = False (Retroactive)

  The first stage is not switched On until the required load is equal to its load factor. Each subsequent stage is not switched until its load factor is required. This mode is normally required for equipment without modulating control, for the control of electric heaters, for example.

  Figure 2. Retroactive Control
  

  

  
  

Setting Make/Break Limits

When the Calculate Make Break Limits property is True, it allows the rated capacity and differential to be set in % data by unit.

Remaining Output and Vernier

As the Input increases from 0% to Make Limit 1, the Remaining output is equal to the Input, and Stage 1 is OFF. When Make Limit 1 is reached, Stage 1 turns ON, and the Remaining output becomes zero. As the Input continues to increase, the Remaining output increases (Remaining = Input - Make Limit 1). The same behavior occurs between each Make Limit n (Remaining = Input - Make Limit n).

The Vernier output is the Remaining output, rescaled from zero to one hundred percent.

Pump Down

Pump Down is an output (Solenoid Valve Out) used to switch a refrigeration circuit ON and OFF. In order to perform this function, the refrigeration equipment MUST have compressors, a Normally Closed Solenoid Valve in the liquid line (between Condenser and Expansion Valve), and a Normally Closed Low-Pressure switch in the suction line (between Evaporator and Compressor).

This output is optional and typically used as follows.

To stop the unit, the solenoid valve is closed (de-energized), and the compressor continues to run until the low-pressure switch trips, which switches the compressor OFF. This leaves a high-pressure drop across the installation when stopped.

To restart, the solenoid valve opens, and the low pressure increases until the Low Pressure switch trips back allowing the compressor to restart.

With pump down active, the Solenoid Valve Out operates as follows:

During plant stop, the Solenoid Valve Out is closed, the compressor continues to run until the low pressure input goes ON, then the compressor stops.

During plant restart, the Solenoid Valve Out is opened first, when the Low Pressure input goes OFF, then the first Stage of the sequence is switched ON.

Single Oil Pump

Some refrigeration circuits have a single oil pump for a group of compressors. In this case, an oil pressure line is available to make oil available to each compressor. Since the pump is mounted on one of the compressors and driven by its motor, this compressor needs to be switched ON first and connected to Device 1 Out. In this case, the first stage is always excluded from sophisticated sequences. When Device 1 Enable is false, the entire sequencer is shut down at once. When Oil Pump on Device 1 is true, then Device 1 Out is always started first.

In addition, an output (Oil Pump Out) to turn on a separate oil pump is provided. This output is used when a common oil pump operated separately from the compressors is provided. Oil Pump on Device 1 must be false for this output to be turned on. This oil pump starts before any Device n Out is activated, and runs for an adjustable period of time before the Device n Out outputs turn on. This oil pump stops after last Device n Out is deactivated, and runs for an adjustable period of time.

This output is optional and typically used as described in the previous example.

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 Inter-stage 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 Inter-stage On Delay between each stage. When an increase in the current stage occurs, the Inter-stage On Delay starts.

If an Inter-stage Off Delay is active when a make limit is exceeded, it does not prevent the stage up. When a stage up occurs, any active Inter-stage 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 Inter-stage 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 Inter-stage Off Delay between each stage. When a decrease in the current stage occurs, the Inter-stage Off Delay starts.

If an Inter-stage On Delay is active when a break limit is exceeded, it does not prevent the stage down. When a stage down occurs, any active Inter-Stage 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 Inter-stage 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.

Inter-Stage 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 inter-stage 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 Inter-stage 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 Inter-stage 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 Inter-stage On delay is active, the stage down occurs if the device to be deactivated has no active minimum on timer.

The Inter-stage 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 Inter-stage 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 Inter-stage Off Delay.

Stabilize Timing

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

When an Inter-stage 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.

The sequencer allows for individual stabilization timers for each stage (for example, Stage 1 On Delay = 300, Stage 2 On Delay = 120, Stage 1 Off Delay = 180, Stage 2 Off Delay = 60).

Stabilize timing occurs when the input exceeds a Make Limit or drops below a Break Limit.