Error In Measured Value - Fuji Electric Time Delta-C FSV-2 Instruction Manual

6.5.4. Error in measured value

Status
The reading appears with
"-" (minus).
Measured value
fluctuates though flow
rate is constant.
Measured value remains
the same though flow
rate is changing. (LED lit
in red)
Probable cause
 Connection between main unit and
sensor units (upstream,
downstream) are inverted.
 Flow of fluid is reversed.
 Straight pipe length is inadequate.
 Pump, valve or others which
disturb the flow are located nearby.
 Pulsation exists in flow.
Measured value is held because ultrasonic wave cannot be propagated into a pipe.
1. Incomplete installation
 Error in piping specifications
 Sensor is mounted on
welding.
 Error in sensor mounting
dimensions
 Error in acoustic coupler at
the time of mounting the
sensor
 Error in connection of the
sensor cable.
Sensor mounting is poor
 Mounting dimension
 The sensor is coming off the
pipe.
2. Problem on pipe or fluid

Pipe not filled with fluid

Bubbles present in the fluid
Bubbles are introduced if reading
is normal when flow is stopped.
If mounted immediately
downstream a valve, a cavitation
causes the same phenomenon
as when bubbles are introduced.
Connect properly.
Move the sensor to the place where the
length of 10D can be assured on
upstream side and 5D on downstream
side.
Mount the instrument with a clearance of
30D or more.
Set the damping to increase the response
time.
Upon checking, remove the sensor,
apply acoustic coupler, and slightly off
position the sensor.
 Mount the sensor in parallel with
pipe, allowing correct sensor unit
spacing.
 Mount the sensor properly so that it
is kept in close contact with the pipe.
Locate a place which is completely
filled on the same piping line, and shift
the sensor there.
 Attach the sensor to the lowest place
on the pipeline.
Eliminate ingress of bubbles.
 Raise the level of the pump well.
 Check the shaft seal of the pump.
 Retighten the flange of negative
pressure pipe.
 Arrange so that fluid doesn't fall into
the pump well.
Move the sensor to the location where
air bubbles have not entered.
 Inlet side of the pump
 Upstream side of the valve
(Continued on next page.)
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Troubleshooting