tekmar 264 Boiler Control - Manual (Page 16)

© 2008 D 264 - 12/08 16 of 32
Section G1
External Input
Section G: External Input Operation
Section G1: External Input
EXTERNAL INPUT
The control can accept an external DC signal in place of the outdoor sensor. The control converts the DC signal into the appropriate
boiler target temperature between 50°F (10°C) and 210°F (99°C) based on the External Input Signal and Offset settings. To use
the external input signal, the External Input / Stand Alone DIP switch must be set to External Input.
1
Com
–
2
Do Not Apply Powe
r
Boil
Sup
3
Boil
Ret
4
Out
+
1
Com
–
2
Do Not Apply Powe
r
Boil
Sup
3
Boil
Ret
4
Out
+
0 - 10 V (dc)
or
2 - 10 V (dc)
0 - 20 mA
or
4 - 20 mA
500 Ω
–
+
–
+
When operating in the external input mode, an external signal is required
in order for the control to provide heat to the heating system. An external
signal is generated by applying a voltage between 0 V (dc) and 10 V (dc)
across the Out + and Com – terminals (4 and 1). Once voltage is applied,
the External Input Signal pointer is displayed in the LCD and the control
closes the primary pump contact. The control calculates a boiler target
supply temperature based on the external input signal and the settings
made in the control. The control then fires the boiler(s), if required, to
maintain the target supply temperature. If the external signal goes below
the minimum voltage, the External Input Signal pointer is turned off in the
display. The boiler target temperature is displayed as “ – – – “ to indicate
that there is no longer a call for heating. The primary pump and boiler
pumps operate as described in section C.
INPUT SIGNAL
The control can accept either a 0 - 10 V (dc) signal or a 2 - 10 V (dc) signal. The External Input Signal setting must be set to the proper
setting based on the signal that is being sent to the control.
0 - 10 V (dc) or 0 - 20 mA
When the 0 - 10 V (dc) signal is selected, an input voltage of 1 V (dc) corresponds to a boiler target temperature of 50°F (10°C). An
input voltage of 10 V (dc) corresponds to a boiler target temperature of 210°F (99°C). As the voltage varies between 1 V (dc) and 10
V (dc) the boiler target temperature varies linearly between 50°F (10°C) and 210°F (99°C). If a voltage below 0.5 V (dc) is received
the boiler target temperature is displayed as “ – – – “ indicating that there is no longer a call for heating.
A 0 - 20 mA signal can be converted to a 0 - 10 V (dc) signal by installing a 500 Ω resistor between the Out + and Com –
terminals (4 and 1).
2 - 10 V (dc) or 4 - 20 mA
When the 2 - 10 V (dc) signal is selected, an input voltage of 2 V (dc) corresponds to a boiler target temperature of 50°F (10°C). An
input voltage of 10 V (dc) corresponds to a boiler target temperature of 210°F (99°C). As the voltage varies between 2 V (dc) and 10
V (dc) the boiler target temperature varies linearly between 50°F (10°C) and 210°F (99°C). If a voltage below 1.5 V (dc) is received
the boiler target temperature is displayed as “ – – – “ indicating that there is no longer a call for heating.
A 4 - 20 mA signal can be converted to a 2 - 10 V (dc) signal by installing a 500 Ω resistor between the Out + and Com –
terminals (4 and 1).
OFFSET
The Offset setting allows the boiler target temperature to be fine tuned to the external input signal. The control reads the external
input signal and converts this to a boiler target temperature. The Offset setting is then added to the boiler target temperature.