OPTIONAL FEATURES HeatNet Control V3
Page 59
Using the 4-20 mA input
(OPTIONAL)
The 4-20 mA 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 4-20 mA
transmitter to control multiple boilers. A free-floating 250
ohm resistor is viewed by the BMS (or external control’s) 4-
20 mA transmitter across the + and –4-20 mA terminals with
this method.
Example: 4–20 mA connections
4–20 mA enable connection
Closing this contact enables
the 4-20mA/0-10VDC input
The 4-20 mA input uses a 250 ohm sense resistor to convert
the current to a voltage from 1 to 5 volts DC for the control to
use. For this reason, a 1-5 VDC control voltage may also be
used across the 4-20 mA +/- input, but it still needs to supply
the necessary current, i.e. 20 mA. This resistor is located on
the bottom side of the control board. When a 4.02 ma 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 0-10 position (UP) See:
Figure 51, the 4-20 mA input will accept a 0-10 VDC signal.
The channel will also need to be setup in the menu:
SETTINGS: 4-20 mA INPUT: CHANNEL MODE. The
operating range will be from 2-10 VDC or twice what was
previously stated for the 1-5 VDC functionality. To convert a
0-10VDC signal to mA, divide by 2510 (ohms).
NOTE: Due to the inability of control voltage methods (1-5,
2-10 VDC) to reject noise and compensate for line loss, the
use of the 4-20 mA 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 4-20 mA transmitter
for operation, connect the 4-20 mA 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 4-20 mA REMOTE
ENABLE inputs on the associated boiler(s).
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