nVent RAYCHEM Elexant 4010i/4020i User Manual
RAYCHEM-AR-H60624-40X0iOpsManual-EN-1905
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CHAPTER–4
4. SAFETY LIMITER
4.1
Safety Limiter
The safety limiter option (-LIM option of the Elexant 4020i, see Table 2 - Elexant 4020i Variants) provides
a redundant high temperature cut-out mechanism, suitable for use in safety critical applications. It dis
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connects power from the heater, preventing the system from exceeding a safe
temperature level.
4.1.1
Safety Function of the Limiter in the Elexant 4020i
The safety function is invoked when the temperature limit is reached, or in the event of a fault (such as
probe break, probe short-circuit, component failure, or supply failure) even when the process conditions
are within the permissible temperature range. The safety function disconnects power to the attached
equipment without delay.
Power may be restored to the attached equipment by manually resetting the safety function after the
temperature returns below the permissible limit and no fault is present. The safety function may be reset
using the TRIP RESET button on the front of the unit, or by using the product GUI, or through supervisory
software connected via the communication ports.
In specific circumstances where there is no current flowing through the heat trace during the over-
temperature event, a feature called Intelligent Limiting (if enabled) will allow the limiter to reset itself once
the temperature returns below the permissible limit and no fault is present.
4.1.2
Area of Use
Safety limiters are used in areas where thermal processes need to be prevented from overheating, and
where the system must be set to a safe operating condition in the event of a fault. A typical example of
such an installation is surface heating in a hazardous area.
4.1.3
Block Diagram
Figure 27 - Safety Limiter Block Diagram
