tekmar 420 Boiler Reset Module - Manual (Page 16)

© 2007 D 420 - 08/07 16 of 24
In some cases, multiple boilers may be required. In these
cases, the 420 allows for a connection to a tekmar Boiler
Control 264, 265, or 268. The 420 uses the modulating
output to provide a 0-10 V (dc) signal to the external input
terminals on the Boiler Control. The 420 controls the Boiler
tekmar Stager Operation Section D
Boiler Motor Speed
The Boiler Motor Speed is the amount of time the boiler
requires to go from 0% modulation to 100% modulation.
Gas valve actuating motors have a design time from fully closed
to fully open which can be found in the manufacturer’s manual.
The Boiler Motor Speed should be set to this time.
The Boiler Motor Speed setting for a Variable Frequency
Drive (VFD) is the amount of time required to go from a
stopped position to 100% fan speed. Since a VFD has a
very quick response rate, it may be necessary to increase
the Motor Speed setting in order to increase the stability
of the boiler modulation.
•
• Locate the Boiler Motor Speed setting in the Adjust menu.
Minimum Modulation
The minimum modulation defines the minimum output
signal from the control to the boiler burner. It is based on
a percentage of the control’s output signal range.
The Minimum Modulation default setting is 0%.
For boilers with electronic operators, the boiler’s input signal
range may not match the output signal range of the 420
control. The Minimum Modulation setting limits the control
output range in order to match the boiler’s input range.
•
• Locate the Minimum Modulation setting in the Adjust menu.
To calculate the Minimum Modulation, use the following
formula:
For 0-10 V (dc):
Minimum Modulation =
0 V (dc) – Boiler’s Minimum Input Signal x 100%
0-10 V (dc)
Example:
A boiler requires a 1.8 V (dc) signal to fire the boiler at
low fire. The boiler can be modulated to 10 V (dc) where
it reaches high fire.
This means the boiler’s input signal range is 1.8 to
10 V (dc). The 420 control has an output signal range of
0-10 V (dc).
To make the two signal ranges the same, the Minimum
Modulation required is:
Minimum Modulation = 0 V-1.8 V x 100% = 18%
0 V-10 V
1.8 V (dc)
10 V (dc)
Control Rang
e
Boiler Rang
e
0 Vdc
18%
Maximum Modulation
The maximum modulation defines the maximum output
signal from the control to the boiler burner. It is based on
a percentage of the control’s output signal range.
The Maximum Modulation default setting is 100%.
For boilers with electronic operators, the boiler’s input signal
range may not match the output signal range of the 420
control. The Maximum Modulation setting limits the control
output range in order to match the boiler’s input range.
•
• Locate the Maximum Modulation setting in the Adjust
menu.
To calculate the Maximum Modulation, use the following
formula:
For 0-10 V (dc):
Maximum Modulation =
0 V (dc) – Boiler’s Maximum Input Signal x 100%
0-10 V (dc)
Example:
A boiler’s input signal range is 2-9 V (dc). The 420 control
has an output signal range of 0-10 V (dc).
To make the two signal ranges the same, the Maximum
Modulation required is:
Maximum Modulation = 0 V-9 V x 100% = 90%
0
V-10 V
10 V (dc)
Control Rang
e
Boiler Rang
e
0 Vdc 0 V (dc)
2.0 V (dc) 20%
90%
Voltage (dc) 0 1 2 3 4 5 6 7 8 9 10
Boiler Target Off 50°F (10°C) 68°F (20°C) 86°F (30°C) 103°F (40°C) 121°F (50°C) 139°F (60°C) 157°F (70°C) 174°F (80°C) 192°F (90°C) 210°F (99°C)
Control target temperature by changing the voltage signal.
The Boiler Control responds to the boiler target by staging
the multiple boilers.
The following table can be used to convert a 0-10 V (dc)
signal to a boiler target temperature: