Slant/Fin EM-10 Service Manual - Manual (Page 11)

11 EM-40-SM Service Manual
A 0-20 mA signal can be converted to a 0-10 V (dc) signal
by installing a 500 Ohm resistor on the external input signal
device’s terminals.
2-10 V (dc) or 4-20 mA External Input Signal
The external input signal can be selected to be either 0-10
V (dc) or 2-10 V (dc) range. When the 2-10 V (dc) range 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 an
internal heat demand.
A 4-20 mA signal can be converted to a 2-10 V (dc) signal
by installing a 500 ohm resistor on the external input signal
device’s terminals.
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.
Section F: External Direct Drive Operation
When mode 8 is selected, the control allows for an external
control to operate the boiler through an analog direct drive
input signal provided by a boiler sequencing control such as
a tekmar Boiler Control 275. When in mode 8, the
external heat demand (CD and Ht D) and the setpoint
demand (CD and Set D) are disabled.
DIRECT DRIVE INPUT SIGNAL
An external boiler sequencer provides a positive 0-10 V (dc)
input signal to the control +V(in) input. The negative V (dc)
signal is applied to the Com/- input.
The boiler burner remains off while the direct drive input
signal range is between 0 to 0.5 V (dc). The Stage 1 contact
remains on as long as the direct drive input signal is over 0.5
V (dc). The Stage 2 contact is activated once the direct drive
input signal reaches or exceeds 3.0 V (dc). Stage 3 contact
is activated once the direct drive input signal reaches or
exceeds 5.5 V (dc). Stage 4 contact is activated once the
direct drive input signal reaches or exceeds 8.0 V (dc).
PUMP OPERATION
The pump is turned on as soon as the direct drive input
signal reaches 0.5 V (dc). Once the direct drive input signal
falls below 0.5 V (dc), the pump continues to operate until
the Pump DLY purge expires, then the pump shuts off.
BOILER OUTLET MAXIMUM TEMPERATURE
The external boiler sequencer is able to operate the boiler
temperature. However, the BOIL OUT MAX setting limits
the highest temperature at the boiler outlet sensor. Should
the boiler outlet temperature exceed the BOIL OUT MAX
setting, the Stage contacts are opened to shut off the
burner. The burners remains off for the minimum off time
and the boiler outlet temperature falls 2°F (1°C) below the
BOIL OUT MAX setting.
0-10 V (dc) 0-20 mA* Boiler Target
0 0 --- (OFF)
1 2 50°F (10°C)
2 4 68°F (20°C)
3 6 86°F (30°C)
4 8 103°F (39°C)
5 10 121°F (49°C)
6 12 139°F (59°C)
7 14 157°F (69°C)
8 16 174°F (79°C)
9 18 192°F (89°C)
10 20 210°F (99°C)
*requires a 500 ? resistor
2-10 V (dc) 4-20 mA* Boiler Target
0 0 --- (OFF)
1 2 --- (OFF)
2 4 50°F (10°C)
3 6 70°F (21°C)
4 8 90°F (32°C)
5 10 110°F (43°C)
6 12 130°F (54°C)
7 14 150°F (66°C)
8 16 170°F (77°C)
9 18 190°F (88°C)
10 20 210°F (99°C)
*requires a 500 ? resistor
Example Range = 0-10 V (dc)
Input = 7 V (dc) 157°F (69°C)
Offset = + 5°F (3°C) + 5°F (3°C)
Boiler Target = 162°F (72°C)