5
Mode 6 (MODE = 6)
Mode 6 is designed for external boiler control. This mode of opera-
tion allows for an external control to operate multiple boilers equipped
with a BC-1. The BC-1 is used to provide boiler pump control. Once
a heat demand is present, the control closes the Stg 1 Stg 1 contact
and operates the boiler pump. Refer to section E for a description of
external boiler operation.
BOILER DIFFERENTIAL (DIFF)
An on / off heat source must be operated with a differential in order to
prevent short cycling. The boiler differential is divided around the boiler
target temperature. The first stage contact will close when the water
temperature at the operating sensor is 1/2 of the differential setting
below the boiler target temperature, and will open when the water tem-
perature at the operating sensor is 1/2 of the differential setting above
the boiler target temperature. The remaining stages will operate sequen-
tially based on the staging mode selected.
STAGING MODE (STGMODE)
The BC-1 controls can operate up to four stages in order to supply the required target temperature. The method of staging used by
the control is either P (proportional) or PID (proportional & Integral & Derivative), and is selected using the STGMODE item in the
Adjust menu. PID is recommended and it is the default setting.
Proportional (P)
Proportional staging, also known as step staging, is based on manually adjusted settings which determine when the next stage
is required to turn on. These manual settings are based on temperature and time. The interstage differential sets the temperature
drop at which the next stage turns on. However, in order for a stage to fire, the interstage delay on and minimum off times must
first elapse.
Interstage Differential (STG DIFF)
The interstage differential is the temperature drop at which the next
stage will turn on. Once a stage turns on, the next stage cannot turn on
until the temperature drops the interstage differential below the tem-
perature at which the previous stage turned on. The interstage differ-
ential is adjustable through the STG DIFF setting in the Adjust menu.
Interstage Delay On (ON DLY)
The interstage delay on is the amount of time that must elapse
before turning on the next stage. Once a stage turns on, the next
stage cannot turn on until the interstage delay on time elapses. The
interstage delay on is adjustable through the ON DLY setting in the
Adjust menu.
Interstage Delay Off (OFF DLY)
The interstage delay off is the amount of time that must elapse before turning off the next stage. Once a stage turns off, the
next stage cannot turn off until the interstage delay off time elapses. The interstage delay off is adjustable through the OFF
DLY setting in the Adjust menu.
Minimum On Time (MIN ON)
The minimum on time is the minimum amount of time that a stage must be on before it is allowed to turn off. Once a stage turns on, it
cannot turn off until a minimum on time elapses. The minimum on time is adjustable through the MIN ON setting in the Adjust menu.
Minimum Off Time (MIN OFF)
The minimum off time is the minimum amount of time that a stage must be off before it is allowed to turn on. Once a stage turns
off, it cannot turn on until a minimum off time elapses. The minimum off time is adjustable through the MIN OFF setting in the
Adjust menu.
Proportional & Integral & Derivative (PID)
PID staging allows the control to determine when the next stage is required to turn on. The BC-1 automatically determines the
settings that are manually selected in proportional staging mode. After each stage is turned on in the firing sequence, the control
waits a minimum amount of time before turning on the next stage. After the minimum time delay between stages has expired, the
BC-1 examines the control error to determine when the next stage is to fire. The control error is determined using PID logic.
Proportional compares the actual operating sensor temperature to the boiler target temperature. The colder the temperature, the
sooner the next stage is turned on.
Integral compares the actual operating sensor temperature to the boiler target temperature over a period of time.
Derivative determines how fast or slow the operating sensor temperature is changing. If the temperature is increasing slowly,
the next stage is turned on sooner. If the temperature is increasing quickly, the next stage is turned on later, if at all.
Boiler Inlet
Sensor Boiler Inlet
Sensor
Boiler Outlet
Sensor Boiler Outlet
Sensor
B
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B
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Time
Supply Water Temperature
Differential = 10˚F (5˚C)Target temperature
160˚F (71˚C)
165˚F (74˚C)
160˚F (71˚C)
155˚F (68˚C)
