EC: Liquiphant FailSafe FTL8x Point Level Measuring System

Safety - Process safety, intrinsic safety: The Liquiphant FTL8x level switch monitors minimum and maximum liquid levels in critical applications, meeting SIL3 with a single instrument. This is a Control Engineering 2014 Engineers’ Choice award winner.

October 17, 2013

The calibration-free two-wire loop powered 4 to 20 mA dc point level measuring system addresses a broad range of critical applications in vessel overfill/underfill and pump (empty pipe) protection even in hazardous locations. Capabilities including safe failure fraction (SFF) >99% and average diagnostic coverage (DC) > 95% support homogeneous redundant as well as 1oo1 SIL 3 operation that can be validated via simple in-situ partial proof testing procedures extending full proof testing intervals up to 12 years. Detection of liquid levels in environments with temperatures from -75 to 525 F and pressures from vacuum to over 1400 psi are addressed.

A companion component to the system FTL825 Nivotester can be used to monitor the 4 to 20 mA analog signal from the Liquiphant to provide output relays for control and fault. The Nivotester also monitors a unique live current signal superimposed on the analog loop by the Liquiphant to provide continuous monitoring of its availability. These features provide diagnostics that meet SIL3 in a stand-alone instrument. When a typical level switch fails, tanks, pipes or vessels can overflow or pumps run dry. To prevent this, the Liquiphant FailSafe FTL8x level measuring system has redundant circuitry and built-in diagnostics that monitor the tuning fork-type sensor for most kinds of failures including, electronic failures, damage, corrosion, material build-up and mechanical blocking. If a problem occurs, the unit will notify the operator via its 4 to 20 mA dc or companion fault relay which can send a signal to an annunciator or PLC, and a combination of three LEDs on the housing indicate the problem so that the switch can be cleaned, repaired or replaced.

Thanks to these technical advances, the Liquiphant meets SIL3 requirements in accordance with IEC 61508, IEC 62061, IEC 61511-1, ANSI/ISA 8400.01-1 and DIN EN ISO 13849, and is certified by TÜV Rheinland.