Teledyne 4250, Installation And Operation Manual, Page: 145 / 204

4250 Flow Meter
Section 5 Maintenance and Service
5-5
5.3 Care of the AV Sensor
and Cables
The area-velocity sensor and its cable require little periodic
maintenance unless there is a great deal of debris in your flow
stream. Certain materials that swell when wet, such as sawdust,
can clog the ports of the probe, blocking the hydrostatic pressure
of the stream from reaching the transducer.
The pressure transducer is on the bottom of the probe. If you
remove the mounting plate from the probe body, you will see a
protective plate attached with two screws. The pressure trans-
ducer is behind this disk. In general, it should not be necessary
to remove this disk, and Teledyne Isco strongly recommends that
you do not. In the standard AV sensors, removing the plate will
expose the paper-thin diaphragm of the transducer. Read the fol-
lowing sections carefully before attempting to disassemble the
probe.
CAUTION
If you disassemble the AV sensor for cleaning, do not touch the
stainless steel diaphragm with your fingers or tools. The dia-
phragm is very thin (<0.003"), and easily bent.
The slightest deformation may result in damage to the trans-
ducer or the placing of a permanent offset on it. In either case
the AV sensor will be ruined. Do not drop the assembly or sub-
ject it to any physical abuse.
5.3.1 Low Maintenance The pressure transducer, the ultrasonic transducers, and the
electronic components of the area-velocity sensor are encapsu-
lated in plastic resin and are not user-serviceable. If any part of
the sensor fails, contact the Teledyne Isco Service Department.
It may be beneficial to periodically clean the flow stream up- and
downstream from the area-velocity sensor to maintain the hydro-
static conditions on which the level measurements and
level-to-area conversions are based. The sensor was designed to
expose a small frontal area and a streamlined profile to the flow,
and that reduces the possibility of accumulating deposits of solid
materials.
5.3.2 Cleaning the Standard
AV Probe
Rarely, organic materials may become jammed inside the AV
sensor’s liquid ports. If this material swells as it becomes satu-
rated with water, it may cause inaccurate pressure transmission
to the level sensor. In the unlikely event that both entrance ports
in the AV sensor become blocked with material that does not
permit the pressure above the probe to be transmitted to the
pressure transducer, you can clean the sensor with the following
procedure:
1. Remove the AV sensor from the flow stream.
2. Scrape any accumulated solids from the exterior of the sen-
sor body with a brush.
3. Remove the three screws holding the sensor carrier plate
to the bottom of the probe. Be careful not to lose the small