8
AW T 210
H A R T 2- W I R E T R A N SM I T T ER | CO M/AW T 2 10/H A R T- EN R E V. B
… 4 Installation
Multi-drop mode (digital) signal and power wiring (loop current mode enabled)
Refer to Figure 3 for a typical wiring configuration for multi-
drop installations. In the multi-drop mode of operation, the
analog 4 to 20 mA is not used. Instead the transmitter draws a
constant 3.6 mA of current to maintain operation.
• Do not connect secondary communication device directly
across the power supply.
• Add 1 V DC to all minimum supply voltage values if using the
TEST connections.
• The maximum number of transmitters is 63.
+
+
–
–
+– +–
+– +–
System power supply
High impedance
controller, recorder
or control system
HART compatible hand-
held terminal (secondary
communication device)
250
ohms
Transmitter 1
Transmitter n
Figure 3 Digital mode wiring diagram
In the multi-drop mode, the process variable signal of each
transmitter on the signal bus is digitally polled. The primary
communication device sequentially polls each transmitter
output on the bus. Each transmitter has its own unique
address that is assigned during configuration. The address
(1..15) allows the primary communication device to distinguish
between transmitters on the bus.
Each transmitter on the bus is wired from the primary
communication device to the positive (+) and negative (–)
POWER (SIGNAL) terminals of the AWT210. Connect all
transmitters on the bus in parallel.
The minimum power supply voltage required for the loop is
typically determined by:
• minimum voltage supply = 14 V + (0.004 A x R)
• minimum current supply = 0.004 A x T
Where:
• R is the Load Resistance in ohms, and
• T is the number of transmitters on the bus
IMPORTANT (NOTE)
The equation for minimum supply voltage is based on
a maximum output current of 4 mA. In some cases
other transmitters may use a multi-drop minimum
current of greater than 4 mA. Consult the vendor
product instruction for multi-drop current values for
other equipment on the bus..
The load resistance must include the system input resistance
and the resistance of the wire. Analog meters or measurement
devices should not be connected to the bus since the
transmitters on the bus are not delivering an analog process
variable.
A secondary communication device can be connected anywhere
there is access to the signal wires, as long as it is not connected
directly across the power supply.
IMPORTANT (NOTE)
Only one secondary device can communicate on the
loop at any given time.
Sensor wiring and grounding
Refer to the AWT210 Operating Instructions (OI/AWT210-EN)
for sensor wiring and grounding instructions.