Infrared thermocouples are IS
October 2001
Sensors & Transducers
The IRt/c falls into the category of thermocouples since it generates its signal by converting the radiated heat energy to an electrical signal via Seebeck effects, the basic driving force of thermocouples. Like all thermocouples, it requires no power source and generates signals measured in millivolts of voltage, microamps of current and nanowatts of power. IRt/cs have a small capacitance, but at 1 µF, the energy storage is measured in nanojoules and is a thousand times lower than the 25 µJ criterion.
Accordingly, the IRt/c qualifies as a simple apparatus for use in hazardous locations and, with the appropriate barrier, qualifies as intrinsically safe.
'Field apparatus having energy storing or generating characteristics of <1,2 V, 0,1 A, 25 mW or 25 µJ shall be considered simple apparatus (nonenergy storing). These general-purpose devices may be used in a hazardous (classified) location without further approval when connected to a certified intrinsically safe circuit.' - Quote from R. Stahl, Inc. Comprehensive Product Manual on intrinsic safety barrier and repeater relays.
Examples of nonenergy-storing intrinsically safe apparatus are:
* Thermocouples, RTDs, LEDs.
* Dry switch contacts.
* Namur inductive proximity switches.
* Noninductive strain gauge devices and resistors.
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