CommStat
™
4
Modbus Adapter
Installation & Operation
Page 3
General Description
T
he self-contained Marvair
®
Modbus Interface Adapter
provides an Ethernet or a serial gateway to the
Marvair
CommStat
™
4
HVAC controller through which an external host can read and write information
from the
CommStat 4
as if it were a Modbus TCP or Modbus RTU device. It is powered by 24VDC or
48VDC. The external host located, for example, within a Network Operations Center (NOC), can monitor
and control the operation of the HVAC units connected to the
CommStat 4
controller. The adapter supports
CommStat 4
controllers with protocol version 3 or later with software revision 67 or later.
The adapter includes (see figure 1):
•
Flange-mount enclosure with the interface adapter
•
15ft (457cm) two-conductor power cable
•
15ft (457cm) RJ11 cable for connection to the CommStat4 unit
•
15ft (457cm) Cat5e cable for Modbus TCP connection to the external monitoring system
•
15ft (457cm) Serial cable for Modbus RTU connection to the external monitoring system
Installation
The adapter can be mounted at any convenient location within the shelter. Mounting ears with pre-drilled
holes are provided on the base of the adapter to allow it to be installed directly on a shelter wall or within
an equipment enclosure. The Cat5e Ethernet, serial communication,
CommStat 4
communication, and
power cables supplied with the adapter are each 15ft. (457cm) in length. The adapter should be mounted
to ensure that the distance from end connection points to the adapter does not exceed 15ft. (457cm)
including all necessary conduit routing. Note that the adapter must be installed inside the shelter; it is not
suitable for installation either inside an HVAC unit or where exposure to external weather is possible. The
adapter is installed as follows:
•
Mount the adapter inside the shelter using the four pre-drilled screw holes on the adapter base.
•
Run the two-conductor power cable (grey insulation) to a suitable DC power source. The adapter
can be powered by 24VDC or 48VDC. The black wire is +24/48VDC and the white is VDC RTN.
•
Remove the lower cover from the
CommStat 4
controller. Plug the RJ11 connector on the flat, black
CommStat 4
communications cable into one of the two Master communications ports at the middle,
bottom of the
CommStat 4
circuit board. Note that if the shelter has two
CommStat 4
controllers,
one of these ports may already be used for the master/slave connection. Reinstall the lower cover
of the
CommStat 4
controller. See Figure 3.
•
Remove the six screws from the cover of the adapter then remove the cover. Turn the breaker on
the power feed circuit to the On position and verify that the red LED on the processor board is On.
If the red LED is not On, turn the power feed circuit breaker to the Off position, swap the black and
white wires at the DC power source, then turn the breaker to the On position. The red power LED
will now be On. See Figure 2. Reinstall the cover.
DO NOT make the power connections with power applied to the feed circuit. This can create electrical
arcing and cause permanent damage to the circuit boards. ALWAYS make electrical connections with the
feed circuit breaker in the Off position and after verifying the absence of voltage with a meter.
