Source:
http://www.flow-network.com
WHAT IS THE CALORIMETRIC PRINCIPLE?
The calorimetric principle is a means of monitoring
flow rates through thermal energy dispersion.
Typically the measurement involves two PTC thermistors
embedded in the probe tip or wall of the sensor. One
of the PTC thermistors (the reference thermistor) monitors
the temperature of the medium being measured (air, water,
oil, etc.) while the other is heated a fixed percentage
above the reference thermistor. This sets up a differential
resistance between the two.

Assume now that the probe tip is sitting in still
air in a pipe or duct. The differential resistance is
established by the electronics and everything remains
stable until flow begins to occur. When this happens,
the flowing air cools the heated thermistor, thus changing
the differential resistance between the two thermistors,
proportional to the flow speed. The amount of energy
that the electronics uses to attempt to maintain the
established differential resistance (by increasing power
to the heater of the dynamic thermistor) is used to
determine the flow rate. This is then translated into
a switching or transmitter output.
“Calorimetric” thus can be described as
measuring flow through use of “thermal dispersion”
(think of the term “calorie” or unit of
heat.)
For further information on the calorimetric principle
see the following article at our website
http://www.flow-network.com/leak_detection.html
3000 SERIES VENT-CAPTOR
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- Flow rates as low as 0-3 ft per second or
as high as 0-200 ft per second, the 3000 series
air flow switches and transmitters address applications
that other technologies can’t.
- Eliminate sticking or breaking or bending
of the air sensor, so common with sail switches
or other mechanical air flow monitors.
- Simple to install
- In stock with SAME DAY Shipping
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Additional advantages of the 3000 series vent-captor
are:
- Can not be damaged by too high an air flow as can
mechanical types
- Repeatability <1% as there is no friction or
mechanical hysteresis
- Self compensate for changes in pressure (mass flow
unit)
- Small, space saving, compact design
- Simple to install
- AC or DC ranges (switches and transmitters)
- Self contained, no auxiliary amplifiers or linearizers
needed.
Common Applications
- Sensing cooling airflow to cabinets or electronic
housings
- Fume hoods in industrial applications such as soldering
stations
- Air Handling equipment, dust collection systems
- Monitoring filter conditions – signal when
change is needed
- HVAC systems for air balancing or flow detection
- Air circulation proving in rail and other transportation
industries
- Compressed Air flow monitoring
- Call us today and let us help you with your air
flow monitoring application.
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