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1.2 DESCRIPTION OF OPERATION
Rheotherm
flow instruments are available with various nonintrusive and intrusive transducer designs,
but they all use the same thermal sensing technique. Two temperature sensors are used — one is in
thermal equilibrium with the fluid and provides a fluid temperature reference, while the second
temperature sensor is located near a heater so that its temperature is slightly above that of the fluid. In
a TU or TUL transducer, the temperature sensors and heater are attached to the outside of the flow tube,
whereas the dual and single probe transducers have the sensors and heater located in the probe(s) that
are inserted into the stream. The amount of heat removed from the heated sensor by the stream is related
to fluid velocity. Hence, the measured temperature differential between the reference sensor and heated
sensor is a function of flow rate. Intek, Inc. is licensed to use this patented and trademarked flow
measurement technique. The Model 400 electronics converts this temperature difference and a portion
of the fluid temperature signal into a temperature compensated and scaled flow output signal. The
signal, for most cases, is proportional to the logarithm of flow rate. Intek also utilizes a proprietary
electronic time constant enhancement technique. When enabled, this feature decreases the time required
to detect the loss of flow by as much as a factor of ten (10).
Example of
Example of
Example of
dual probe
single probe
nonintrusive transducer
NPT/2I
NPT/I
(TU-style)
1.3 PRECAUTIONS
1.
Use proper input power — Check the label on the electronics for the input power
requirements.
2.
Use reasonable care in handling the transducer. Do not try to disassemble the transducers;
there are no removable parts.
Probes (NPT/2I, NPT/I, BF/2I, BF/I, etc.) — take care not to bend the probes or damage the
tips. Do not try to remove or turn the conduit junction box.
TU or TUL — twisting or bending can damage the sensor. The flow tubes are thin-walled
tubing.
3.
Check the transducer maximum temperature rating — do not operate a transducer at or subject
it to a temperature outside of its specified limit(s).
4.
Keep moisture out of the electronic enclosure and sensor junction box. Once cable
connections are made in the junction box, make sure the lid is tightly closed. Seal conduit
lines if they can become wet inside.
