Application Note

Application Note: 101405A

Fail Safe

Application:

Wiring and configuring the CLASSIC 800 Series Flow, Level, Interface & Temperature Switch & Transmitter for "Fail-Safe" operation

Product:

Kayden CLASSIC 800 Series Thermal Dispersion Flow, Level, Interface & Temperature Switch & Transmitter

Description:

The term “Fail-safe” refers to a method of wiring and programming control instrumentation commonly used in hazardous locations / applications such as a chemical plant, gas plant or refinery.

Problem:

In a “Fail-safe” application the instrument is wired and configured to be “ON” (closed contacts, output(s) supplied by the instrument to the system) during normal system operations, but “OFF” (contact(s) open or de-energized, output(s) discontinued) in the event of a power failure, cable break, self-test failure, or other loss of electrical power.

Solution:

A common “fail-safe” set up for No Flow Condition, Pump Protection:

Connect the relay contact wires to Normally Open (R1NO, R1CM)1
Electronic instruments such as capacitance probes, ultrasonic, and radar level controllers are bothered by vapors, bubbles, coating, require constant attention, are more expensive, and are often difficult to install.
Depending on application and set-up of the switch transmitter, the relay contact(s) will OPEN (deenergize):
1. When the thermal signal decreases due to a decrease or loss of flow/level
2. When power is lost to the switch as described above.

Notes:

The Kayden CLASSIC provides wiring terminals for Normally Open and Normally Closed outputs, as well as the ability to set (locally via the Display Panel or remotely via the RCM Software) the relay contact(s) to energize above or below set point(s).
The RELAY LEDs are illuminated when the corresponding relay is energized.