Teledyne 4220 - Manual (Page 92)

4220 Flow Meter
Section 3 Installation
3-10
mersion when the stream is high, you should protect the desic-
cator and the reference port by venting them at a point the water
cannot possibly reach.
Remember that water or other blockage inside the submerged
probe's vent tube will ruin the submerged probe. It is even more
important to protect the Quick-Disconnect Box this way than the
flow meter, because of the likelihood that the submerged probe
will be directly connected to the Quick Disconnect Box. When
connecting the probe directly to the flow meter, you may use an
extension cable, which would offer some protection to the sub-
merged probe.
3.5 Extension Cables The standard (10 foot depth) probe for the 4220 has a 25-foot
cable. The 30 foot depth probe has a 50-foot cable. If these
lengths are insufficient, Teledyne Isco offers extension cables for
use with the probes. There are two different lengths available:
one is 25 feet long; the other is 50 feet long.
CAUTION
The submerged probe extension cables and the submerged
probe cable cannot be cut for any reason, or they will be
ruined. The connectors are factory-sealed and neither the
shielding nor the vent tube inside can be satisfactorily spliced
in the field.
CAUTION
Teledyne Isco does not recommend connecting multiple exten-
sion cables together in an attempt to exceed the 75 foot limit.
Increasing the length of the vent tube beyond 75 feet slows the
response of the pressure transducer, and this may cause mea-
surement errors. For greater distances, use the Quick-Discon-
nect Box and a custom-built cable.
The submerged probe uses a differential pressure transducer.
The cable connecting the submerged probe to the flow meter con-
tains a small tube that references the pressure transducer to
atmospheric pressure. This allows a true differential pressure
measurement unaffected by changes in barometric pressure.
This tube is vented through the connector into the cabinet of the
4220 Flow Meter. From there, it is vented to the atmosphere
through a desiccant cartridge mounted on the side of either the
flow meter or the Quick-Disconnect Box.
3.6 Safety Considerations In field installations of 4220 Flow Meters and associated
equipment, the safety of the personnel involved should be the
foremost consideration. No project is so important or deadline so
critical as to justify the risk of human life.
We urge you to read the safety procedures provided in Appendix
D.