When Endress+Hauser invented the vibronic principle nearly 50 years ago,
it paved the way to safe and reliable level monitoring.
More than four million Liquiphant point level switches have since been installed worldwide, becoming the number one choice for safety-critical applications. Now Liquiphant FailSafe offers functional safety up to SIL3 in a single device.
Liquiphant’s initial advantage over float switches and other passive devices was its ability to sense its own condition by detecting vibrations even when in an uncovered state. This increased safety because it was able to detect failure of the device before the alarm condition was reached.
Later developments expanded on this, allowing the frequency of the tuning fork to be continually monitored. A change in oscillation above or below a permitted variable indicated irregularities of the fork, for example corrosion damage or product build up. This automatically trigged a safety-oriented switching of the instrument.
As process requirements and legislative changes introduced industry to risk assessments and Safety Integrity Levels, the Liquiphant range was ideally placed to satisfy these requirements. The level switches were qualified to SIL2 for both low level pump protection duties and high level overfill protection.
SIL3 applications Whilst most industrial applications are, by good practice, engineered down to a SIL2 level there are still occasionally high-criticality SIL3 applications. These high risk processes may require a voting system or redundancy system where multiple sensing devices are used to achieve the higher level of confidence. For example, two Liquiphants could be installed at the same point, reducing the probability that an unsafe condition goes unnoticed. However, this results in a need for more signal cabling, more installation points, more system inputs, and an increased possibility of false alarms.
As a result of continuing research and development, Endress+Hauser is now able to offer the Liquiphant 80 series that is qualified to SIL3 for a single device. The product offers the highest functional safety with a Safe Failure Fraction (SFF) greater than 99%.
Simple functional safety The design of the device duplicates components, providing internal redundancy where required to achieve these high levels of reliability. So now you only need one process connection and one set of cabling and system input to achieve SIL3 levels of safety. The output signal also complies with the latest safety standards in accordance with NAMUR NE06 and NE43, giving easy integration with either the separate Nivotester FTL825 or directly connected to a safety PLC.
The evaluation of this system now gives an extended proof test interval of 12 years, reducing testing costs. In many cases this even exceeds the expected plant lifetime. To avoid situations where the microprocessor is locked but is giving a valid output, further outputs are continuously calculated in the form of a low frequency or heartbeat signal superimposed on top of the 4-20mA signal. This output is continuously monitored by the control system or Nivotester, giving further confidence in the signal and eliminating problems from processor lockups indicated by failure of the superimposed signal. This ensures the system is functioning correctly. Documentation to prove the safety of the system is also available.
For more information please email sales@uk.endress.com or call us on 0161 286 5050