Teledyne 4250, Installation And Operation Manual, Page: 43 / 204

4250 Flow Meter
Section 2 Programming
2-15
Enter a value for the vertical distance the probe is installed
above the true zero level of the flow stream. For example, if the
probe is mounted on the side of the pipe at a point one foot higher
than the true zero level (at the bottom of the pipe), the zero level
offset is one foot. See Figure 2-3.
Figure 2-3 Measuring Offset Distance
Note
Do not confuse the circumferential distance between true zero
and the location of the probe with the vertical difference
(height). If you install the probe at the true zero level of the pipe
or channel, you would enter
0 for the offset. Refer also to the
installation section for the area-velocity sensor.
If you select ZERO FLOW ON ERROR, the following will appear:
When the 4250 flow meter cannot obtain a valid flow mea-
surement, it will report an error. This option tells the 4250 how
to respond to an error measurement. The object is to select the
option that gives you the greatest overall accuracy.
Selection of YES will make the 4250 register zero flow until the
next valid measurement can be made. Selection of NO will make
the flow meter continue to use and display the last valid mea-
surement prior to the ERROR reading. An error measurement
does not necessarily mean that there was actually no flow. It
simply means that the flow meter was unable to obtain a valid
measurement. This can occur when the velocity drops too low to
measure or the probe is buried in sludge. ZERO FLOW ON
ERROR will report errors if the level is below minimum depth.
Selection of YES or NO depends on your situation. If you are
running a sampler with the flow meter and velocity is at times so
low as to be almost non-existent, you would probably select YES
(set flow to zero) to prevent the flow meter from tallying unreal-
istic flow totals to prevent the sampler from taking unrepresen-
Offset Distance
Area Velocity Sensor
True Zero Point
of Channel
Circumferential
Distance
ZERO FLOW ON ERROR
• YES • • NO •