DFM-400P Rev 2.1 Installation and Appplication Guide Edition 1.6
Page 7 of 14
Mounting
The DFM-400P includes a plastic enclosure that can be mounted quickly and easily with two screws in an
appropriate location, or within another enclosure (to meet code requirements).
The Rev 1.2 DFM-400P enclosure can be snapped into a 35mm DIN rail.
Input Wiring
Pulse Inputs on the Pulse Input Field Module follow the same general wiring diagrams for dry contact
and open collector connections as other Delta products. Refer to separate documentation for additional
details.
Power
The Pulse Input Field Module requires a 24 VAC @ 2 VA power supply, typically an isolated Class II
transformer. More than one device – not including DCUs or V2 products – may be connected to the same
transformer, providing the transformer is properly sized, including line losses, and polarity is observed
between controllers (in regards to 24~ and GND). The transformer must ONLY be used to provide power
to other MS/TP devices. Auxiliary field devices (i.e., 4-20 mA devices) that don’t use ½ wave rectification
must be powered separately.
Network & Cabling Requirements
To ensure network stability and reliable communications, particularly at high speeds on a BACnet RS-
485 MS/TP network, it is imperative that you adhere to the following network and cabling requirements:
Item
Description
Cabling
For BACnet MS/TP networks it is recommended that you use network cabling that
matches the following specifications:
•
Balanced 100 to 120 ohm nominal impedance Twisted Shielded Pair (TSP) Cable
•
Nominal capacitance of 16 PF/FT or lower
•
Nominal velocity of propagation of 66% or higher
Topology
For BACnet MS/TP networks, ensure the cable is installed as a
daisy-chain
from one
device to the next.
Max. Nodes
The maximum number of devices per BACnet MS/TP network without any repeaters
is
50
.
Termination
Boards
A termination board
must
be installed at each end of each BACnet MS/TP network
segment – or two per BACnet MS/TP network. Ensure you do not overlook this in
laying out your network architecture and ordering product.
Repeater
A repeater (RPT-768) is not necessary unless more than 50 nodes will be installed on
a network
or
you need to extend the network beyond 4000 ft (1220 m).
For more detailed information, including wiring, refer to the Delta Controls Wiring and Installation Guide
