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Technical Notes
#10  IRt/c's are Intrinsically Safe When Used with Barriers
"Field Apparatus having energy storing or generating characteristics of 1.2V, 0.1A, 25 mW or 25 microJ shall be considered Simple Apparatus (non-energy 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 non-energy storing Intrinsically Safe Apparatus are:
Thermocouples, RTD's, LED's
Dry Switch Contacts
NAMUR Inductive Proximity Switches
Non-inductive Strain Gauge Devices and Resistors
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 thermo-couples. Like all thermocouples, it requires no power source and generates signals measured in millivolts of voltage, microamps of current and nanowatts of power. IRt/c's have a small capacitance, but at one microFarad, the energy storage is measured in nanojoules and is a thousand times lower than the 25 microjoule criterion. Accordingly, the IRt/c qualifies as a Simple Apparatus for use in hazardous locations, and with the appropriate barrier, qualifies as Intrinsically Safe. The official Intrinsic Safety Letter can be opened here.
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