Make A Fail Safe System - ProMinent DULCOMETER PH-501 Assembly And Operating Instructions Manual

SAFETY PRECAUTION (capacitance) Step Four
Make a Fail Safe System: Design a fail safe system that accommodates the possibility of switch and/or power
failure. FLOWLINE recommends the use of redundant backup systems and alarms in addition to the primary
system. Adding a redundant high level float switch to the system is a cost effective means to prevent costly
tank overflows.
All of the Switch Tek™ Powered Level Sensors have a single internal relay. The normally open (NO) or
normally closed (NC) operation is user selected based on the desired system control. Always design a fail safe
system that accommodates for the possibility of functional and/or power failure to the instrument. The
"normal" relay state is where the relay coil is de energized and the relay indicator is OFF. Therefore, if power is
cut OFF to the switch it will de energize the relay. Make sure that the de energized state is the safe state in
your system design. As such, if switch power is lost, a pump will turn OFF if it is connected to the normally
open side of the relay.
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