KROHNE VFM 3100 EN - Manual (Page 34)

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4.4. Preamplifier
The Preamplifier assembly (shown in Figure 22) consists of the pre-
amplifier with a shield for integral mounted electronics (or with a mo-
unting plate for remote mounted electronics, as shown in Figure 23).
The preamp has a sensor switch which must be set to STD for stan-
dard temperature sensors and set to EXT for extended temperature
range sensors.
4.4.1. Preamplifier Removal Integral Mounted VFM 3100
• Disconnect power from the VFM 3100.
• Remove electronic module compartment cover (opposite “Field
Terminal” side) and remove the electronic module as described
starting on page 30. Remove the brown, red, orange and yellow
preamplifier leads. Refer to Figure 18. It is not necessary to re-
move the display, if one is present.
• Cut the two tie wraps holding the preamplifier leads and signal
leads together.
• Pry the retaining tabs of the metal shield away from the housing,
using a straight blade screwdriver, and pull the whole assembly
out. See Figure 22.
• Turn the preamplifier upside down, disconnect the yellow and
brown sensor leads from the terminal block, and loosen the
strain relief clamp that holds the sensor cable.
• Pull the preamplifier out of the housing.
NOTE: For CENELEC certified flameproof VFM 3100, disconnect
preamplifier ground lead from housing. Save screw and lockwasher.
See Figure 21.
• Remove the Preamplifier from the shield by removing the two
screws. See figure 22. Save the two screws and metal shield.
• The replacement procedure starts on page 35.
Screws
Retaining tabs
Preamplifier
Metal shield
Figure 22. Preamplifer Assembly - Integral Mount Extended Tempe-
rature Range
Remote Mounted VFM 3100
See next section for remote mounted CENELEC version.
On remote mounted electronics, the Preamplifier is housed in the
junction box on top of the VFM 3100. The Electronic Module is in the
transmitter housing.
• Disconnect power to the VFM 3100.
• Remove the junction box cover. The Preamplifier and a 4-posi-
tion two-sided terminal block are mounted on a round plate in
the junction box, as shown in Figure 23.
• Disconnect (brown-red-orange-yellow) wires from both sides
of the terminal block and remove strain clamp holding remote
cable.
• Disconnect yellow and brown sensor leads from terminals on
the preamplifier and loosen strain relief clamp holding the sensor
cable.
• Unscrew the two mounting screws to remove the mounting
plate from the junction box.
• Turn the mounting plate (with the preamplifier) upside down and
unscrew the two screws to remove the preamplifier. Save the
screws and the mounting plate assembly.
Remote Mounted CENELEC Certified Flameproof VFM 3100
• Remove power from the VFM 3100 . The transmitter and
junction box of a remote mounted CENELEC certified flame-
proof VFM 3100 have locks on their covers as shown in
Figure 24.
• To remove the Preamplifier, remove lock assembly of junction
box and remove cover. The Preamplifier with a metal shield over
it, a 4-position two-sided terminal block, and metal ground strap
are mounted on a round plate in the junction box.
Mounting
screw
Screws
Terminal
wire
Sensor wire
Mounting
screw
Preamplifier
wires
Figure 23: Preamplifier Assembly - Remote Mount Assembly.