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  Submitted Articles: ARTC05082801
Article: What is this thing called calorimetric?
Submitted by: Larry Flanagan
Submit date:28/08/05
What is this thing called calorimetric?

In the $3 billion dollar world market of flow metering, a little known jewel is gradually finding its way to acclaim.the calorimetric flow sensor. The use of the calorimetric principle in flow is now a standard in the industry. Significant advances over the past decade have enabled the calorimetric sensor to assume a very active and respected role in flow switching and flow metering of both liquids and gaseous mediums.

The most common use of these sensors is in flow no-flow applications for detecting the movement of air or liquids. Popular for their solid state construction with no moving parts, the calorimetric flow sensor is impervious to particulate matter that spells doom for mechanical type devices.

Historically, the calorimetric switching devices have been costly in comparison to mechanical switches, but with new technological breakthroughs in both electronic and mechanical construction, there are, now available, units that compete directly with their primitive counterparts.

Traditional Paddle Switch
Modern Calorimetric sensor
Flow metering has also become a substantive part of the calorimetric sensor's function. The sensing technology, having no moving parts, allows measurement of flows so low as to be below the inertia threshold of turbine or paddlewheel sensors. This has made them very popular for chemical dosing, leak detection, etc. Also, extended range calorimetric sensors are now available that can enable measurements of much higher flow rates (up to 60 feet per second for some liquids) than previously thought possible with calorimetric technology.

The traditional calorimetric technology utilizes two PTC Thermistors, one of which is heated a predetermined amount above the other, which monitors the medium temperature. Flow of the medium conducts heat away from the sensor probe and the corresponding change in the heated Thermistor's resistance value is then amplified, linearized and converted into an output (switching or analog depending upon sensor type) proportional to the rate of flow.

The fact that calorimetric sensors do not require the medium to be electrically conductive (as would a mag meter for example) makes measurements of polymers, oil, grease, and numerous other mediums possible. The technology also is not based upon suspended particles for measurement accuracy (as would be the case with doppler type meters). The addition of optional specialty metals for use in the calorimetric construction (such as Hastelloy, Monel, Titanium etc.) allows measurements of innumerable aggressive medium such as chemicals and acids.

The calorimetric sensor's minimal power requirements have enabled the development of battery operated flow sensors for remote locations. These can be paired with wireless transmission devices to enable internet based monitoring or dial up fault alarming for such applications as loss of flow to pumps, leaking of pipes, and loss of lubrication oil flow or coolant flow in transportation.

Inherent in the design is the continual monitoring of the medium temperature, which enables the calorimetric sensor to also function as a temperature monitor. This provides the user with two sensors in one. This has been a popular feature with chiller manufacturers, as the same device can alarm if flow is lost, or temperature exceeds predetermined limits.

Microflow technology in calorimetric sensors has also enabled here-to-fore unrealizable low flow metering of less than 2 milliliters per hour of liquid flow.

In summary, the calorimetric flow sensor is the rising star of the flow sensing industry and offers capabilities unmatched by other flow measurement technologies.

Larry Flanagan

 


This article was submitted by Larry Flanagan