Aalborg PWE Digital - Manual (Page 14)

9
2.4 PWE MAINTENANCE
CAUTION: Some of the IC devices used in the flow meter signal
conditioning circuitry are static sensitive and may be damaged by
improper handling. When adjusting or servicing the signal converter,
use of a grounded wrist strap is recommended to prevent inadvertent
damage to the integral solid state circuitry. The flow meter signal
conditioning circuitry uses complex electronic circuit components.
Generally, due to the complexity of troubleshooting integrated circuit
devices, maintenance beyond the PCB assembly level is not
recommended. Also, caution must be used when connecting test
probes, as even a momentary accidental short circuit may damage or
destroy an integrated circuit device.
ƽ
CAUTION: Never use compressed air or gases to test the meter,
as this would damage the Bearings.
ƽ
2.4.1 Sensors
In rare instances, due to electrical damage, the pulse sensor or RTD need to be
replaced by disconnecting the signal cable connector from the PCB and unscrew-
ing it and installing a replacement. This procedure can be done only by factory
authorized personel.
2.4.2 PWE Paddle Wheel and Bearings Replacement
To replace the paddle wheel, disconnect the meter from electrical and liquid lines.
Unscrew 4 screws that hold the lid in place. Remove the lid by lifting it up and
move the wheel out. The Wheel’s embedded shaft is supported at each end by sap-
phire bearings to minimize friction and facilitate very low flow rate measurements
(see Figure 2-1). Reassembly is made ensuring that the shaft end is inserted gen-
tly into the bottom bearing. Check to see if the wheel is free to spin before the lid
is installed. Gently put the lid over the opening and gently spin it by hand until the
upper bearing, installed in the lid, drops into the place. Hold the lid down and
check for free spinning by lightly blowing into the port; or lightly shake and listen
if both shaft ends got into the bearings. Make sure the O-ring is in its seat, insert
four cap screws and gradually tighten them. Bearings are made of sapphire, which
rarely needs replacement, unless they were physically shattered. Bearings highly
susceptible to careless disassembly and reassembly practices. While the unit is
disassembled for paddle wheel replacement, bearing could be replaced with bear-
ing removal tool.