HVAC sensors meet ammonia demands
An
American Sensor Technologies product story
Edited by the Engineeringtalk editorial team
Mar 5, 2007
AST's sensors can cope with the demands of ammonia refrigeration pressure measurement.
American Sensor Technologies (AST) offers a variety of products to be integrated into HVAC and refrigeration equipment.
The AST solution begins with a one-piece, stainless steel construction that contains no internal seals or gaskets.
Additional features include a high cyclical life (over 100 million full cycles), long-term stability and compound ranges with linear output through zero.
Each product ensures a high level of EMI/RFI protection, in addition to holding hazardous area approvals, RoHS compliance, and is listed under UL/cUL standards.
Due to customer demands, AST is responding to ammonia refrigeration pressure measurement requirements.
Refrigeration pump and compressor manufacturers are moving towards the improved efficiency of ammonia over freon-based systems.
However, the thermodynamic behaviour of ammonia is very different from freon.
When the refrigeration pump turns on, the ammonia temperature rapidly changes.
This accelerated change, along with the type of sensor diaphragm materials affects the pressure transducer performance and ultimately the control system.
O-ring sealed pressure sensors cannot withstand rapid thermal changes and over time the internal O-ring will fail.
Fluid-filled sensors suffer from freezing effects, which lead to the rupture of the diaphragm membrane.
Thin-film sensors that have their diaphragm welded to a pressure port, will undergo thermal stresses that will eventually crack the steel.
Thermal flash protection is the technology applied by AST to reduce the effects of thermal flash transients when the media is ammonia.
First, AST utilises its one-piece stainless steel sensing element with 316L-wetted materials.
This element is free of welds, oil-fill and internal O-rings.
Next, a special non-clogging port design is used in order to minimise the extreme temperature change.
The sensor will recognise a uniform temperature as to maintain system stability.
AST offers other HVAC/R solutions, including an SAE4 (7/16-20 UNF) female pressure port that contains an internal Schraeder depressor pin.
This port allows the sensor to be easily removed or installed in service, eventually eliminating the need for adaptors.
AST also manufactures additional pressure ports, such as 1/8-inch NPT, 1/4-inch NPT and SAE4 male.
Common applications for AST products are refrigeration pump controls, chillers, freon and ammonia cooling systems, high-pressure wells, boiler controllers and environmental testing.
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