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When the least expensive component fails ....... |
November 16, 2005 |
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Posted by Joe Lewis at November 16, 2005 08:36 AM |
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As a senior member of ISA (Instrument Society of America) for the past couple of decades I get InTech magazine monthly. A recent article in the November 2005 issue (pp 67) entitled "A level experience" indicated that "dumb switches" used for indicating the presence or absence of material at a predetermined point could not be provided with self-diagnostics and had no way of communicating whether they were working. The article suggested that these point level indicators must be physically tested to ensure that they still work. Is this really true? These level indicators tend to be the least expensive, or at the very least a low cost, component within a storage or material handling system. Can it be expected that they will have a long life (more than one year) and also be self-validating?
What happens when the $200 rotary paddle level indicator (click here) fails? Or even the $300-400 RF capacitance point level sensor (click here)? If these units are utilized as high level indicators, an overfill condition could occur if they have failed and you are not aware of it. There could be damage to other expensive equipment such as filters and conveying systems or just a large clean-up job waiting for you. If point level indicators are used for detecting a low level condition and they fail without any notice, then you might run out of material and lose production. Either way, the failure of this low cost component without notification can cost you money and lost profits.
Coincidentally in the same issue of InTech magazine there is another article on pp 45 entitled "Beyond mere measurement". This article discusses the benefits of field devices (level indicators are considered "field devices") with self-diagnostics and the use of asset management software to improve plant profitability. In fact the article mentions a reference document/book entitled "An Introduction to Predictive Maintenance" (pp 46 of "Beyond mere measurement") where the author claims that in excess of $200 billion per year is spent on maintenance of plant and equipment in the USA alone. He claims that this represents lost profits in excess of $60 billion! Wow, that's a chunk of change!
So, what does that mean to us in the powder and bulk solids processing industries? My point is simple. Reliability of the least expensive components is very important. It is worthwhile to consider a device that DOES incorporate reliable self-diagnostics. But wait a minute, did the first article mentioned above say that dumb switches couldn't provide this? Well, for powder and bulk solids point level detection this isn't the case.
Truly fail-safe rotary paddle devices are commonly available from at least three or four sources. The most reliable of these is the SafePoint fail-safe rotary paddle unit (click here) that uses patented Hall effect sensor technology to determine its own health status on a continuous basis. In addition, a dedicated relay output is provided and the contacts can be monitored to inform you of a device failure. Knowing whether the device is operational or whether it requires maintenance can save you a tremendous amount of time and money.
Consider using a true fail-safe unit with reliable self-diagnostics. I call these devices "self-validating" because they not only evaluate their health state but tell you what that state is.
Joe Lewis
Vice President
Monitor Technologies LLC
jlewis@monitortech.com
www.monitortech.com
