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INTRINSICALLY SAFE SYSTEMS
RSS design, manufacturer, install and commission Intrinsically Safe -
Intrinsic Safety is the method of protection for control and instrumentation circuits where the nominal voltage is 24 or less and the current is normally less than 100 mA. The concept of intrinsic safety is to limit the voltage and current so that there is never a spark with enough energy to create an explosion.
Intrinsic safety when properly used removes the ignition from the explosion triangle. There are three components to an intrinsically safe circuit: the field device, intrinsically safe barrier and field wiring.
• Field devices known as intrinsically safe apparatus is classified as simple or complex.
• Simple apparatus, which do not need to be approved, are non energy storing devices such as contacts,
thermocouples, RTDs, LEDs and resistors
• Complex apparatus such as transmitters, solenoids, relays and transducers may store excess energy and
need to be approved by a third party
• Contacts, transmitters and temperature sensors are the most commonly used field devices in intrinsically
• The intrinsically safe barrier limits the current with a resistor and the voltage with a zener diode
• Intrinsically safe circuits are designed so that they operate properly under normal conditions, but keep the
energy levels below the ignition curves when a fault condition occurs.
There are three components to a barrier, that limit current and voltage: a resistor, at least two zener diodes, and a fuse. The resistor limits the current to a specific value known as the short circuit current, ISC. The zener diode limits the voltage to a value referred to as open circuit voltage, Voc. The fuse will blow when the diode conducts. This interrupts the circuit, which prevents the diode from burning and allowing excess voltage to reach the hazardous area. There are always at least two zener diodes in parallel in each intrinsically safe barrier. If one diode should fail, the other will operate providing complete protection.
RSS also supply IS Pressure Transmitters and Proximity Switches and other IS instrumentation allowing IS control to be used in hazardous locations, reducing the need for bulky cabling, glands and enclosures.
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IS Electrical Systems Presentation
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