Campbell Scientific CR7 Measurement and Control System - Manual (Page 145)

14-1
SECTION 14. INSTALLATION
14.1 ENVIRONMENTAL ENCLOSURE,
CONNECTORS AND JUNCTION
BOXES
The standard CR7 is equipped with the Model
ENC-7F Fiberglass Case. During the
manufacturing of the case, the base and lid are
formed together to insure a perfectly matched
fit. A six digit serial number is stamped into the
extruded aluminum rims on both the base and
lid. When more than one CR7 is owned, care
should be taken to avoid a mismatch which
could prevent a gas-tight seal.
In addition to the AC power input connector and
pressure relief valve, the STANDARD ENC-7F
enclosure has two 1.040" dia. access ports,
located to the left side of the I/O Module (Figure
OV.1-1). These access ports are provided to
allow the entry of sensor leads, power cables,
etc. Unless otherwise specified at time of
ordering, these two access ports are fitted with
0.75" dia. conduit bushings, 0-Ring seals and
removable neoprene plugs. The neoprene
plugs can be used to form a reasonable seal by
drilling holes in them for accommodating the
passage of sensor leads to the I/O Module.
NOTE: Users wishing to punch additional
access ports should be aware that the
1.040" dia. punch is a special size. The
greenlee punch normally used to make
holes for 0.75" conduit bushings is 1.07"
dia. This diameter is too large for mounting
the 19 pin connector option.
Access ports fitted with drilled neoprene plugs
may not be sufficient for certain data acquisition
situations. Alternatively, the access ports can
have connectors installed.
Factors which may influence selection of the
appropriate connector type are (1) the seal
required, (2) the permanent or temporary nature
of the CR7 installation, and (3) cost
considerations.
14.1.1 ACCESS PORTS FITTED WITH ELBOWS
Standard 0.75" dia. male conduit elbows may
be screwed directly into the conduit bushings
provided with the standard environmental
enclosure. Elbows allow entry of individual
sensor leads and power cables while preventing
precipitation from entering the enclosure
directly. Silicon sealer can be used to seal off
the space between the elbow wall and leads.
Conduit elbows are inexpensive and well suited
for field applications where sensor arrays are
frequently changed and a gas-tight seal is NOT
required.
NOTE: Larger conduit elbows (1.5" dia.)
are required for allowing a 9 pin D-type
connector with ribbon cable attached to
pass through and access port. In order to
accommodate the larger elbows, access
ports must be enlarged and fitted with the
appropriate conduit bushings and O-Ring
seals.
14.1.2 SOCKET CONNECTORS
Access ports may be reconfigured as connector
ports by replacing the conduit bushings with
sealed (shell size 14) 19-pin circular socket
connectors. Individual leads are soldered to the
backside of the mounted connector and routed
to appropriate I/O terminals. Socket connectors
are recommended for applications where a gas-
tight seal IS required.
The connector utilizes a compression screw-
actuated sealing gland. This connector is
recommended when multi-connector sensor
cable is used between the CR7 and a junction
box.
14.1.3 JUNCTION BOXES
Individual sensor leads (and multiconductor
cables) may be routed directly from the sensor
locations to the CR7 or routed to a junction box
and then to the CR7. Advantages of using a
junction box are two-fold: it provides a
convenient method for changing sensors/sensor
leads quickly and can provide additional
protection against instrumentation damage as a
result of lightning induced high voltages.
Junction boxes generally do not require a gas-