Emerson MVS205 Use Instructions page 6

Safe Use Instructions – MVS205
159 mm
Figure 5. MVS205 Pipe Mounting (Vertical Pipe)
6.
To gain access to the terminations in the
MVS sensor, use a 3 mm Allen hex wrench to
remove the cover clamp on the sensor. Then
unscrew the end cap of the sensor.
The interface circuit board in the MVS205
electronics head allows the MVS to connect to
(be powered from) and communicate with a
ROC or FloBoss using a serial 4-wire EIA-485
(RS-485) connection.
The four wires should be a minimum size of 22
AWG and a maximum length of 605 meters.
Table 1. MVS Interface Circuit Terminals
Terminal
A
B
RTD REF
RTD +
RTD –
RTD RET
+
–
The terminals in the MVS205 head are labeled
the same as the terminals on the MVS terminal
block in the ROC or FloBoss. Connect the ROC
or FloBoss and Remote MVS terminals one for
one: A to A, B to B, "+" to "+", and "–" to "–".
Do not reverse polarity of the power wires (+
and –) while wiring the MVS unit.
MVS205ac.dsf
Usage
+ Signal
– Signal
RTD REF
RTD +
RTD –
RTD RET
+ Power
– Power
For the ROC300-series unit, connect the
prefabricated cable from the DPI module to the
communications connections of the ROC300-
series assembly. The MVS Interface Card
(CMA8H) is required as the Communications
Card. Then run four wires from the DPI module
port 2 connection to the MVS. Refer to the
Remote MVS Interface User Manual (Form
A6090).
For the FloBoss 407, run four wires from the
FloBoss 407 MVS terminal block on the
termination board to the MVS sensor.
For the ROC809, run four wires from the
terminal block on the ROC809 MVS module to
the MVS sensor.
In all cases, make connections by baring the
end (6 mm maximum) of the wire, inserting the
bared end into the clamp beneath the
termination screw, and then tightening the screw
to 0.25 N-m.
Pay close attention. Do not reverse the
power wires. Always make these connections
after removing power from the ROC or FloBoss.
Double-check for proper orientation before
applying power. If the connections are reversed
and power is applied, the MVS and the ROC or
FloBoss processor board may be damaged.
7.
Connect the Remote MVS to a suitable
earth ground per applicable codes and
standards. Two means of grounding are
available on the unit: internal and external.
Refer to Figure 2 for the location of the external
ground.
All earth grounds must have an earth to ground
rod or grid impedance of 25 ohms or less, as
measured with a ground system tester. The
grounding conductor should have a resistance
of 1 ohm or less between the MVS205 sensor
head ground and the earth ground rod or grid.
To safeguard against lightning strikes, install a
surge suppression device at the service
disconnect on DC voltage source.
8.
Use an external three- or four-wire RTD to
sense the process temperature. The RTD
sensor is connected directly to MVS
sensor's interface circuit board. A separate
RTD cable assembly is required for the
connection. Refer to Table 1 for the terminal
descriptions.
Form A6154
Page 4