Vector Equipment Sales » Instrumentation

Is it really "safe"?

Joe Lewis — Wed, 15 Sep 2010 22:46:05 +0000

Having spent the last 35 years of my life immersed in a wide variety of aspects in the process measurement and control industry I was recently asked for a recommendation regarding a level control device that would be able to control a bin filling operation and be "safe". What a soapbox I was handed.

The powder and bulk solids industry seems as though it lags in adopting some technology, at least from an instrumentation standpoint. However, it isn't just the risk averse nature of most powder and bulk processors, but it is that much instrumentation technology developed for use with liquids (80% of the overall measurement business in level measurement) does not cross over directly or seamlessly to powder and granular material level measurement. It takes time to adapt technology for the challenges of bulk solids.

The same exists in the area of instrument "safety". Driven by large legal and financial ramifications in the chemical and petrochemical area, as well as standards writing bodies such as the global IEC (International Electrotechnical Commission), most "safety" related approaches are quickly developed and adopted in liquid oriented industries, such as chemical, petrochemical, pharmaceutical etc. So when asked, I summarize the four levels of basic safety regarding the function or output of a level measurement or monitoring device.

I recently posted to the Just Level Expert blog the following list. You might want to setup an RSS feed from that blog so you don't miss anything.

SAFEST: Material detection sensors certified to SIS and SIL according to IEC 61508 and 61511. Refer to this White Paper to explain more about this safety level. There are level indicators certified at this level, but primarily technology for liquid applications. It's an interesting subject if you are involved with process safety. Check it out.

SAFER: Self-validating level sensor technology that verifies its health and communicates it to you. This is only available with rotary paddle technology for solids and doesn't eliminate moving parts, the drive motor, and comes at quite a hefty price tag. Fail-Safe rotary paddle, RF and vibrating element devices are just as reliable and protect against many sensor failures, those that occur due to power disruptions.

SAFE: Material detection sensors that are FAIL-SAFE so the sensor output indicates an alarm if the power supply to the sensor fails. Rotary paddle units offer the highest value with this capability, but make sure you ask specifically for a unit that has a fail-safe output on power failure. RF and vibrating element sensors commonly provide this capability on a standard basis.

TAKING YOUR CHANCES: This is any material detection sensor that does not offer at least the SAFE level or above. This is common with some brands of rotary paddle bin level indicators, proximity sensors and also with tilt switches and diaphragm switches. Consider switching these out for the "SAFE" kind.

One final point, thinking about relying on your inventory level sensor for control? Don't! And don't take my word, listen to what the accident investigation report said regarding their findings and recommendations regarding the fuel depot explosion and fire late in 2005 that was estimated to cost 1 billion pounds (that's pounds sterling British currency). You can read about that in an editorial column from September 2009.

Got a question? Give us a call at 888-61LEVEL or 815-625-2224. Email us at bluelevel@blueleveltechnologies.com.

Essentials of Modern Measurements —- Book Review

Joe Lewis — Wed, 27 Jan 2010 15:27:05 +0000

“Essentials of Modern Measurements and Final Elements in the Process Industry” is a new book assembled by author Gregory K. McMillan, with a host of contributing writers. I first became aware of this new book from a post at ControlGlobal.com, one of the leading industry news and editorial sites on Internet. I was intrigued by the fact that someone took the time to put a new book together that was about process MEASUREMENT and not control automation. I remember GIGO (garbage-in, garbage-out) and still place a strong priority on measurement technologies rather than the control system. In the end, both are necessary but it is my opinion that many within the Measurement, Control and Automation industry seem to have forgotten about the process measurements and their importance.

I have completed much of the Level Measurement section, Section 5, which begins on page 229 and continues through 273. I have a few observations and constructive comments regarding this section of the book:

MEASURING SOLIDS LEVEL IS ABSENT. This book is definitely well written. My hat is off to the writers of this section on Level Measurement. They and the editor(s) did a fine job in writing the material. The illustrations are also well done. Bravo! However, there is a glaring absence of even a mention of level measurement of powders and bulk solids, which can be just as complex or more complex than liquid level measurements. I view this as a deficit in the book and feel a few pages could have and should have been devoted to this topic. A White Paper on the subject of continuous level and inventory measurement of powders and bulk solids may serve to fill the gap.

ABSENCE OF POINT LEVEL SENSING. Well I guess some folks don’t consider point level “level measurement” and in the strictest possible sense of the phrase it is arguable. However, even third-party market research firms such as Venture development Corporation include point level with continuous level when assessing the Process Level market. This subject should have been included, especially given the introduction of several point level products from a variety of companies rated for SIL-2 use, such as this unit from Magnetrol. I also point to the recent recommendation by the board that reviewed and assessed the aftermath of the Buncefield accident late in 2005. One of the conclusions stated that the failure of the inventory measurement sensor system and the absence of a separate overfill detection and prevention system may have been contributing factors to the accident. Point level sensors have a place within the “level measurement” arena.

FOCUS ON DP, RADAR AND ULTRASONIC. I do agree that these are very important technologies. I also concur that Radar, whether in its contact guided wave form or non-contact form, is the fastest growing technology for level measurement. DP and Ultrasonic also are large segments and heavily used. However, the absence of any discussion about Magnetosrtictive technology, Displacers and only a limited discussion on RF Admittance capacitance type sensors was disappointing, and those are for liquid apps. In addition, the category of smart weight & cable inventory systems, like all else for solids, was absent as well.

I definitely recommend this book as one of the better reference books available. However, I do feel and wished the above deficiencies would have been corrected before publishing.

Joe Lewis
BlueLevel Technologies, Inc.
www.bluelevetechnologies.com
joe@blueleveltechnologies.com

Failure of Tank Overfill High Level System

Joe Lewis — Tue, 21 Jul 2009 23:01:00 +0000

What happens when your high level indicator fails without warning? Everyone knows the answer and we have talked about it before. The unknown failure of a high level sensor that is used for overfill protection can result in an overfilled condition that means lost material, clean-up, damage to equipment and even catastrophic events. People can and have died. This is preventable!

Recent conclusions from the review boards looking at the cause of the explosion at an oil depot in Buncefield England and the explosion a couple of years back at the BP facility in Texas City have cited level detection system failure and the need to utilize equipment meeting IEC 61511 requirements as part of a Safety Instrumented System is necessary. Read the full story here.

Level detection devices meeting SIL2 are commonly available for liquid level applications. However, not for powders and bulk solids. While loss of life may not be as high a risk with powders and solids, it remains a costly occurence to overfill a silo, even with plastic pellets.