tekmar 261 Boiler Control - Manual (Page 8)

Copyright © D 261 - 0
3/09
8 of 20
FIRE DELAY ( Fire Delay)
The Fire Delay is the delay time that may occur between the time that
the 261 closes a stage contact, and the burner fires for that stage. This
delay is usually the result of burner pre-purge, or other forms of time
delay built into the burner’s safety circuits.
BOILER DIFFERENTIAL (BOIL DIFF)
An on / off heat source such as a boiler must be operated with a differential in order to prevent short cycling. With the 261, either a fixed
or an auto differential may be selected.
Fixed Differential
The boiler differential is divided around the BOIL TARGET temperature.
The contact will close when the supply water temperature is 1/2 of
the differential setting below the BOIL TARGET temperature, and will
open when the supply water temperature is 1/2 of the differential setting
above the BOIL TARGET temperature.
Auto Differential (Ad)
If the Auto Differential is selected, the 261 automatically determines
the best differential as the load changes. This setting is recommended
as it reduces potential short cycling during light loads.
WARM WEATHER SHUT DOWN (WWSD) OCC & UNOCC
When the outdoor air temperature rises above the WWSD setting, the 261 turns on the WWSD segment in the display. When the
control is in Warm Weather Shut Down, the
Boiler Demand pointer is displayed, if there is a demand. However, the control does not
operate the heating system to satisfy this demand. The control does respond to a setpoint demand and operates as described in
section C.
Section C: Setpoint
SETPOINT DEMAND
A setpoint demand is required in order for the 261 to provide heat to the setpoint load. The
261 registers a setpoint demand when a voltage between 24 and 240 V (ac) is applied
across the
Setpoint Demand terminals (3 and 4). Once voltage is applied, the Setpoint
Demand pointer turns on in the LCD. The control operates the boiler(s) to maintain at least
the
Setpoint setting. The setpoint demand does not turn on the boiler pump. If a setpoint
load is used, the installer must make sure that the setpoint device provides its own flow
through the boiler(s).
BOILER TARGET DURING SETPOINT (BOIL TARGET)
The BOIL TARGET during a setpoint demand is increased to at least the Setpoint setting. This temperature is maintained as long as
the 261 has a setpoint demand.
Desired temperature
this example
160
°F(71°C)
Cooler
T
emperature
W
armer
Time
Differential
this example
10 °F(5°C)
165 °F(74°C)
155 °F(68°C)
Te
m
p
e
ra
tu
re
fa
ll
BOILER
OFF ON
Te
m
p
e
ra
tu
re
ri
se
Boiler T
emperature
Time
Fire
Delay
Fire
Delay
Boiler Contact Closes
Boiler Fires
Minimum
Off Time
Minimum On Time Minim
3 4
Setpoint
Demand
24 to 240 V (ac)
Off
On
Time
Heating Load
Differential