OPTIONAL FEATURES
HeatNet Control REV 1.38-1
Page 23
Protocessor option
An optional BACnet or LonWorks bridge module can be used
to connect the MODBUS network to a BACnet or LonWorks
network.
Figure 19
MODBUS Connections
This method allows enabling and disabling the boiler or H-
Net system, changing setpoints, reading boiler(s) status, or
temperatures remotely using digital commands. See the
section:
MODBUS Communications
.
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 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.
Figure 20
4-20mA Connections
Figure 21
4-20mA Enable Connection
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
(adjustable) 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 33%(3:1
turndown) or 25%(4:1 turndown) of the boilers output.
If jumper shunt JP3 is set to the PWM/0-10 position, the 4-
20mA input will accept a 0-10 VDC signal (that can source
20mA). 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 500 (ohms).
Due to the inability of control voltage methods
(1-5, 2-10 VDC) to reject noise, 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 20mA 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).
Setpoint Control
functionality can be implemented remotely
using the 4-20mA input. This function translates a 4 to 20mA
control signal to a setpoint mapped from 50F to 220F. The
feature is enabled in the SETPOINTS menu as: SETPT
SOURCE 4-20mA.
ADVANCED SETUP:4-20mA INPUT
. Also, when
selecting;
SETUP:SETPOINTS:SETPOINT SOURCE
and
selecting 4-20mA, the 4-20mA INPUT menu will be
automatically entered.
The current at which the boiler will start can be selected. It is
adjustable from 3.7mA to 5mA. Hysteresis of .1mA is always
in effect. So, if the starting mA = 4.10mA the boiler will start
when the control current applied achieves the value of
4.10mA. The boiler must drop .1mA below this to turn OFF,
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