![]() ![]() Point level instruments in these and other similar applications may have to be periodically proof tested to meet various safety regulations. NAMUR Worksheet NA-106 (Issue: ), Annex D, is typically referenced in the process industries - such as chemical, petrochemical and oil and gas - as well as in other process plants with hazardous operations. NAMUR provides guidelines on what proof testing is needed to meet the requirements of IEC 61508-6, B3.2.5. Early detection allows plant personnel to address issues in a proactive manner prior to failure.Ī proof test confirms the SIL rating of a safety instrumented function. Modern vibronic instruments have built-in diagnostics to detect corrosion and build-up by monitoring the frequency of the tuning fork. But when build-up on the tuning forks becomes excessive, it can cause the device to fail and not detect changes in liquid level. A limited amount of coating changes the frequency of the probe but does not cause it to fail - i.e., a lightly coated instrument can still operate. When tuning forks corrode, they can break off, vibrate erratically or fail completely.īuild-up of process materials on the forks can also occur, especially in processes with entrained solids, turbulence or foam. ![]() Most vibronic instruments are available with tuning forks made of corrosion-resistant metals, such as 316/316L stainless steel, Alloy C22 and PFA coatings, but aggressive chemicals can eventually eat through even these types of materials. Vibronic instruments have no moving parts, so the only physical problems they might encounter are corrosion and build-up of process materials on the tuning forks. Self-monitoring - New vibronic instruments are equipped with internal diagnostics and the ability to automatically perform proof tests and verification. No wear and tear, maintenance-free - A vibronic instrument has no moving parts and requires no maintenance other than periodic cleaning. Unaffected by media properties - A vibronic instrument is not affected by changing flow, turbulence, gas bubbles, foam, vibration, solids content or build-up.Įasy installation and ready for use without calibration - In most cases, a vibronic instrument works in the application without any required adjustments or calibration. Unaffected by media viscosity and density - Vibronic instruments can be used to measure the presence of liquids with viscosities up to 10,000 mm2/s and densities greater than 0.3 g/cm3. Other advantages of vibronic instruments include: In addition, most are corrosion resistant. Unlike float switches, vibronic instruments do not require maintenance and have a long service life. ![]() This allows these devices to be used in critical applications such as overfill protection and pump dry run prevention. In the oil and gas sector, refineries rely on vibronic instruments because they are among the most reliable of measuring instruments. These instruments can be used in storage tanks, containers and pipes for point level detection of all types of liquids. Vibronic instruments are well-suited for liquid level applications, including point detection at the top and bottom of tanks, certified leakage monitoring and overfill prevention, use in hazardous environments and in applications requiring safety integrity level (SIL) two and three certification. The frequency decreases when the fork is covered by a liquid, and this change is analyzed and translated into an on/off output signal by the instrument’s transmitter. The sensor portion of the instrument uses a tuning fork (Figure 2) that’s excited at its resonant frequency of about 85 Hz by a piezoelectric crystal, with a second crystal detecting the vibration produced by the first. Vibronic instruments consist of a transmitter and a sensor. This article describes those developments and shows how they benefit end users. While the basic technology of vibronic instruments hasn’t changed much over the years, today’s instruments now employ technological innovations to bring them into the digital age, meet the needs of Industry 4.0 and the Industrial Internet of Things (IIoT), provide diagnostics themselves and provide access from mobile devices. One instrument manufacturer, Endress+Hauser, produces 330,000 Liquiphant level instruments (Figure 1) each year, and has sold six million units since 1983. Available from multiple manufacturers, millions of these devices have been installed worldwide over the past few decades. Vibrating fork level instruments - also called vibronic instruments - are widely used in the process industries.
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