OPTIONAL FEATURES HeatNet Control V3
Page 60
Using the 4-20mA input (OPTIO NAL)
The 4-20mA input is designed to operate per the ISA-50.1
standard. It will support Type 2, Type 3, and Type 4
Transmitter/Receiver circuits.
The Type 2 and Type 3 circuit may use the supplied +24VDC
and 24VDC RET connections (J10B) to power a remote
transmitter. The –ma terminal will need to have a jumper
connected to the adjacent 24VDC RET terminal to reference
the signal ground.
With the type 4 configuration, multiple boilers (up to 5), may
be connected in series using the –ma +ma –ma +ma scheme
(no jumper to 24VDC RET). This allows one 4-20mA
transmitter to control multiple boilers. A free-floating 250-
ohm resistor is viewed by the BMS (or external control’s) 4-
20mA transmitter across the + and –4-20mA terminals with
this method.
Example: 4–20mA connections
4–20mA enable connection
The 4-20mA input uses a 250-ohm sense resistor to convert
the current to a voltage from 1 to 5VDC for the control to use.
For this reason, a 1-5VDC control voltage may also be used
across the 4-20mA +/- input, but it still needs to supply the
necessary current, i.e., 20mA. This resistor is located on the
bottom side of the control board. When a 4.02mA signal is
sensed, the boiler will initiate a start sequence and fire the
boiler at its minimum setting if the REMOTE ENABLE input
is closed. This is typically 25% of the boilers output (4:1
turndown).
If the dip switch S6 is set to the 0-10VDC position (UP) See:
Figure 51, the 4-20mA input will accept a 0-10VDC signal.
The channel will also need to be setup in the menu:
SETTINGS: 4-20mA INPUT: CHANNEL MODE. The
operating range will be from 2-10VDC or twice what was
previously stated for the 1-5VDC functionality. To convert a
0-10VDC signal to mA, divide by 2510 (ohms).
NOTE: Due to the inability of control voltage methods (1-5,
2-10VDC) to reject noise and compensate for line loss, the
use of the 4-20mA control current is recommended. The
control voltage methods may be less expensive but are the
least stable. If using a 0-10VDC control signal, a source
current of 5mA is required.
If using a remote panel with a relay and a 4-20mA transmitter
for operation, connect the 4-20mA transmitter output from the
remote panel to the member boilers using the floating 250-
ohm method (type 4). The relay contacts on the remote panel
will then be connected to the associated 4-20mA REMOTE
ENABLE inputs on the associated boiler(s).
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