For example:

If its add-stage action has been triggered, it will remain in this condition until either a stage has been added,

Or

The criteria for its being in an add-stage condition is no longer met; only then will it take another look around to see what state it should go to next.

DEFINITIONS

Modulating stage: The modulating stage is the Control System that is receiving varying firing rate requests to track the load.

First stage: This is the Control System that was turned on first, when no slave Control Systems were firing.

Previous stage: The Control System that was added to those stages that are firing Just prior to the adding of the Control System that is under discussion.

Next stage: The Control System that will or might be added as the next Control System to fire.

Last stage: The Control System that is firing and that was added the most recently to the group of slaves that are firing. Typically this is also the modulating stage, however as the load decreases then the last-added stage will be at its minimum rate and the previous stage will be modulating.

Lead boiler: The Lead boiler is the Control System that is the first stage to fire among those stages which are in the equalize runtime (Lead/Lag) group. If a boiler is in the “Use first” group it may fire before the Lead boiler fires.

First boiler: A Control System may be assigned to any of three

groups: “Use First”, “Equalize Runtime”, or “Use Last”. If one or more Control Systems are in the “Use First” category, then one of these (the one with the lowest sequence number) will always be the first boiler to fire. If there is no Control System in the “Use First” category and one or more are in the “Equalize Runtime” category, then the First boiler is also the Lead boiler.

LOCAL OPERATOR INTERFACE: DISPLAY SYSTEM

Figure 49.  BURNER CONTROL S7999B DISPLAY SYSTEM

The S7999B is a microprocessor-based touchscreen Operator Interface (OI) display that provide an operator interface for monitoring and configuring parameters in the Burner Control system.

The S7999B can be used to monitor an individual boiler but is primarily used for multiple boiler applications in a lead/lag arrangement. COM 2 port is available for Building Automation applications. The S7999B display is flush mounted into a panel cutout (8-1/8 in. W x 5-7/8 in. H). Wiring connections to the S7999B are through a removable 9-pin wiring header.

FEATURES

Individual boiler status, configuration, history, and diagnostics.

Allows configuration and monitoring of the Burner Control

Controls burner control sequence, flame signal, diagnostics, historical files, and faults.

S7999B OI Display only:

Allows switching view between multiple boilers

Allows viewing Lead-Lag Master

Ethernet port for downloading software upgrades (when required)

Real-time data trending analysis and transferring saved trend data to Excel spreadsheet.

Audible Alarm

COM 2 Modbus port for Building Automation System applications.

LED indicators:

Power

Network

COM 2

COM 1

Model used:

S7999B1067 has Black Border

49

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A.O. Smith 2600, 3400, 1700, 2000 instruction manual Local Operator Interface Display System, Definitions, Features

3400, 1700, 2000, 2600 specifications

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