OPTIONAL FEATURES
HeatNet Control V3 3.x
Page 62
Using the 4-20mA input
(OPTIONAL)
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 su24VDC
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.
Figure 44
4
–20mA connections
Channel 1:
4-20mA/0-10VDC
(+)
(-)
Channel 2:
4-20mA/0-10VDC
(+)
(-)
24 VDC Return
24 VDC
Figure 45
4
–20mA 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 4-20mA +/- 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 4.02 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 44, the 4-20mA input will accept a 0-10 VDC signal.
The channel will also need to be setup in the menu:
SETTINGS: 4-20mA INPUT: CHANNEL MODE
. The
operating range will be from 2-10 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).
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 4-20mA 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 4-20 mA 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).