Dwyer PSX2 - Manual (Page 156)

147
12.3 Error in measured value
State Cause Remedy
Indication of measured
value is negative (-). • Connection between the main unit
and sensors (upstream sensor and
downstream sensor) is reverse.
Ö Connect correctly.
• Fluid is actually fl owing in the (-)
direction.
Measured value
fl uctuated widely
though fl ow rate is
constant. • Straight pipe portion is inadequate. Ö Shift measurement location to
the site where 10D and 5D can
be secured on the upstream and
downstream sides.
• A fl ow disturbing factor such as
pump or valve is provided in the
vicinity.
Ö Mount the instrument with a
clearance of 30D or more.
• Pulsation is occurring actually. Ö Extend response time through
damping setting.
Measured value
remains the same
though fl ow rate is
changing. • Measured value is held because ultrasonic
wave cannot be propagated into a pipe.
1. Incomplete installation
• Piping specifi cations are wrong.
• Sensor is mounted at the welded
part.
• Sensor mounting dimension is
wrong.
• Grease application at sensor
mounting is incomplete.
• Sensor connector is not connected
completely.
• Pipe surface is contaminated.
Ö
After check, separate the sensor
once. Apply the grease again
and remount the sensor with a
slight shift.
2. Problem on pipe or fl uid
• When V method is used, it should
be changed to Z method.
• When sensor extension cable is
used, it should be avoided.
• If error persists, check and elimi-
nate the true cause as instructed
below.
Fluid is not fi lled. Ö Find the location on the same
pipe line, where fl uid is fi lled
up and move the sensors to that
location.
Mount the sensors at the lowest
location on pipe line.
Bulletin F-9-PUX2