level measurement

Avoid Obstructions When Installing A Guided Wave Radar Sensor

Guided wave radar instruments, like Flexar®, use a cable as a wave guide or antenna.  The microwave energy pulses down the cable antenna and reflects off the material surface.  The reflected pulse travels back up the antenna to the transceiver. 
Obstructions near (within ~12”) of the cable antenna have a high probability of interfering with the microwave energy measurement pulses. Just think of attempting to make a cell phone call while standing inside a metal doorway.  Sometimes it works but most times it doesn’t.
Some obstructions result in crazy reflective echoes.  These reflections can exceed the strength of that from the material surface.  To cancel such large reflection an irritating and often substantial dead zone has to be created along the length of the wave guide cable antenna.  Not good.

Obstructions also cause signal degradation.  Like the cell phone example, energy from the wave guide cable can be bleed off onto the obstruction.  Because the Flexar guided wave radar sensor is measuring and not cooking the silo contents the emitted energy level is rather limited.  If enough of this energy is bleed off there is a possibility that insufficient energy will remain to make a viable reflection.

Vessel View, Exterior

Vessel View, Interior

 

   

Pictured above is one of the most common examples when it comes to interfering obstructions.

For unknown reasons the factory provided application and mounting recommendations were disregarded and the Flexar instrument was mounted to the pictured stub nozzle.  Under the best of circumstances the height of a stub nozzle should not exceed the inside diameter.  In this example that guideline has been completely violated. As shown, the nozzle protruding above and below the roof line well exceed the inside diameter.  This resulted in crazy pulse reflections which were so strong that the level signal would not follow the
material level.  The short term solution required a six foot dead zone to be created on the top portion of the vessel. 
This meant the customer lost the ability to monitor the material in the upper six foot section of the vessel.  Not good. 

The long term solution is to move the Flexar to the  center of the forward plate which sits atop a large nozzle which better conforms to the mounting guideline.

Andy

Technorati Tags: Level sensor level measurement basics bin level indicator level control solids level indicator guided wave radar 

 

A SINGLE Wireless standard for the process industries? Not a chance!

Well here we go again.  I just read some editorials in the latest issue of CONTROL magazine.  Greed and ego are proving to trump logic and reason once again.  Users need a standard, a single open protocol standard for Wireless communications.  In existence today with products being marketed offering this capability are Wireless HART.... that's it.  The Honeywell wireless is a proprietary protocol that Honeywell is batting to shove down the throats of the ISA100 committee that have been gathered for three years now trying to develop a standard.  While the battle has been quietly, and sometimes not so quietly, been raging in the ISA100 committee, Wireless HART has been working hard and growing its installed base.  By the end of 2008 there will be even more products offering it, including the measurement instrumentation giant Endress & Hauser and Emerson Process.  I'm with them, Wireless HART is the way to go... and so is wireless in general.

For level measurement applications, especially those used for inventory monitoring and management, wireless offers the ability to save money by eliminating the cost of hard wiring and also enabling the connectivity of sensor and system across physical barriers to hard wiring.  But this wireless application is not anything new.  Many vendors have been providing wireless communications using proprietary protocols for years.  The new wireless standards hope to offer interoperability from application to application and vendor to vendor.  This is a good idea.

Joe

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Hydrostatic Level Measurement is still "King" for liquids

In a recent article published in CONTROL magazine author and writer Paul Miller makes the point that hydrostatic head pressure measurement is still a most common method for measuring the level of a fluid in a tank.  He makes other points too, more important in his article than here.  The point I wish to make here is that this technology for the level measurement of fluid in a tank has been around for many years and is a simple and economical way to measure tank levels, while its "flash" is far less than newer technologies like radar.

Let's take a quick look at how pressure or differential pressure transmitters are used to measure the level of a fluid in a tank.  Why type when I can reference you to a perfectly fine tutorial from Wikipedia so follow this link.  Some application issues affecting the use and performance of hydrostatic level measurement include the cleanliness of the fluid, the corrosiveness of the fluid and how stable the specific gravity or density of the fluid is.  Like other technologies used for level measurement of liquids, there are limitations.... which is why so many technologies exist today and they are all viable in their own right.... EXCEPT for using ultrasonic to measure continuous level of powders and other bulk solids... No No No!

Really though... please read Paul's article "Pressure-Based Level Measurements Keep Getting Better and Better" because it is well written and a great short tutorial on this subject (it also keeps me from having to write it for you LOL).  It's great and a reminder how these devices work well and some of their limitations.

I went back and took a look at the most recent market study report I have available.  Hydrostatic pressure based level devices represent about 48% of all continuous level measurement devices bought each year!  That's huge!

Joe

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Level measurement basics ..........

Why do level measurement applications provide some of the most difficult challenges?  Why are there so many technologies available?  It should be easy, right?  Not necessarily.  I have never been one to want to say a whole bunch when a picture can say it better, and I sure don't want to say any more when a video is available.

In this blog post I want to highlight a great little ten minute video that I recommend for any engineer that now or ever has had the need to figure out how to determine the level of a material in a vessel.  The video is titled "Back to Basics: Basics of Level Measurement".  Walt Boyes is the editor of CONTROL magazine and a major asset to the publication, their website and the automation industry in general.  I can't say enough good about him.  He is brilliant in many areas of process measurement, control and automation, yet very down-to-earth and he cares about the industry and the people within the industry.  I am honored to name him a freind, one I don't see hardly enough anymore (Walt, how about lunch?).  Anyway.... take a few minutes and watch the video!

If you need to measure the level of a powder and bulk solid I have another more detailed resource for you.  Download this file for the white paper titled Continuous Level Measurement of Bulk Solids (or something close to that LOL).  Download whitepaper_tech_review_of_cont_level_for_pbs_apps.pdf

Joe Lewis

Technorati Tags: Ethanol level sensor level measurement basics bin level indicator level control solids level indicator guided wave radar 

Ethanol plants use a variety of level controls

Ethanol production is at an all-time high in the United States and around the world.  There is a huge amount of research on-going in the field as well to determine what else we can process to turn into a fuel source besides corn.  With the surge in gasoline prices this year a boost to Ethanol has occurred.  While some critics blame the Ethanol industry on increasing grain and food prices, this industry generates thousands of jobs and billions of dollars in the economy for construction and operation of these facilities.  Let's look at where level measurement and monitoring devices are used:

Corn storage silos: Typically using open-air radar or smart weight & cable systems.  Guided wave radar is also a possibility depending on range required.  High level overfill protection can be handled with self-validating rotary paddle technology.

Corn surge hoppers: Application for guided wave radar technology as range is usually less than 30' and atmosphere is very dusty.

Corn grind silos: These applications can also be handled with guided wave radar technology or even open-air radar.

Dryers:  Best fit with RF capacitance point level sensors for high and low level detection.

Many other applications exist and sensors required for measuring level are varied.  Open-air radar, ultrasonic, RF, rotary paddle and other technologies are used.  The manufacturers and contractors that thrive from the construction and operation of Ethanol facilities also benefit greatly from this industry.  Ethanol is good for the USA.  What to know more?  Click here for a Download WhitePaper_EthanolSolutions.pdf free white paper.

Joe Lewis

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Vegetable oil isn't too slipery for guided wave radar

Measuring a wide variety of crude vegetable oils can be a challenge for some continuous level measurement technologies, but it is an ideal application for guided wave radar.  In China crude vegetable oil is brought in by ship and stored in vessels by the Taixing Port Authority.  This port is in Jiangsu Province near Shanghai.  At this facility there are 11 vessels with crude vegetable oil and the port authority needed a reliable way to monitor oil inventories to ensure security and accurate transfer of the oil in and out of the vessels.  Ranges varied from 55 feet and above.

The crude oil is bought by local manufacturers and refined further.  Most oils at the port in this application include palm oil, olive oil and bean oil.  The dielectric constant of these oils are fairly low, around 1.7-1.8 so many technologies will be challenged to work consistently and accurately.  The solution to the measuring challenge came in the way of guided wave radar when a local instrumentation distributor, Conasen, recommended the sensors.  In this application the GWR sensors were outfitted with a RS485 digital communications output and the automation supplier connected this to a PC running inventory management software furnished by a local supplier.  All is working well!  Guided wave radar, good and reliable for liquids and solids as well.

Joe Lewis

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Measuring coal powder levels when nothing else will work ......

Coal-fired power plants are commonplace around the world.  In order for these power generating stations to create huge amounts of electricity the turbines need to be fed with steam and the steam is created boilers fired by ... yep, coal! But coal as it comes from the mining operation is not what is fed to the burners.  First it is ground or pulverized into powder.  It is not unusual for the coal powder to be stored in silos awaiting for the demand for it to be fed to the burners.  The inventory of coal powder in these silos need to be monitored to allow for efficient operation of the power plant.

So, how do we monitor the inventory level of coal powder in a silo?  Not easily.  In one typical application the power plant personnel found that the only technology that would work reliably is the modern smart weight & cable system.

Anhui Tongling power plant in Anhui province, China, had tried almost ever technology possible to get a reliable level measure in their five coal powder silos.  Radar, ultrasonic and others were tried but none worked reliably.  It wasn't until Beijing Conasen walked in and proposed that the Tongling plant use a smart weight & cable system, the one shown in the picture in this post, that they found a reliable solution.

Joe Lewis

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Digital Cameras are a relatively inexpensive and indispensable diagnostic tool.

Those of us that have played the Tech Support Game for any length of time have at some point been in a situation where neither the caller seeking help nor the person trying to render assistance was understanding the other’s inability to comprehend what was being said or asked.  Believe me when I say that that is a situation that can turn volatile in a nano-second.  Especially in the level sensor business, there are some fairly creative ways for end users to improperly install point level sensors in a way that will severely impact the sensors ability to function as it was designed to do. Maybe we will work on a top ten list for later publication. Anyway, what I am doing on a more frequent basis is to ask the customer if they have a digital camera at their disposal. About now you are saying to yourself, “Self, almost everyone with a cell phone has a digital camera these days.”  While this may be true, my experience with the quality of the pictures taken and sent by a cell phone is that the pictures received are very often all but useless due to low resolution of the image.  Some of the newer cell phones have better resolution but there are going to be a large quantity of poor resolution camera phones out there for some time to come.  Almost any off the shelf digital camera is capable of providing the resolution needed to see intricate construction detail of some sensor mounting that was previously verbally obscure in the description of someone speaking a different mechanical language than the other person. When trying to photograph a sensor or sensor mount inside a dark silo, the low lux (low light) capabilities of most digital cameras indeed becomes a huge asset.

Innocent misunderstandings can change the tone of a conversation from friendly to confrontational in a very short time. No one wants that to happen and it can cause bridges to burn so to speak. So, if you find yourself in a situation when either receiving technical help or giving it and someone is not getting (ready for this?) “The Big Picture” (sorry, I couldn't resist J ), consider asking for or volunteer to take a digital picture and email it to the other party. A digital camera is a valuable tool and it can potentially reduce the amount of time it takes for a tech support person to identify a problem and offer a solution.  Best of all, a reasonably capable digital camera that is small enough to fit in a pocket can be quite inexpensive making it quite easy to justify obtaining one.

Take a look at the photo at the top of this blog post.  This photo happened to be taken by one of our service techs but it shows a bad installation for this guided wave radar sensor and explains why it wasn't working properly.  Never extend a nozzle into the silo when installing a guided wave radar level sensor.  The customer could have been talking to us for a long time before he stumbled on this little known fact because the installer and the person we speak with to provide tech support many times aren't the same people.  A picture is indeed priceless and worth more than a thousand words.

Greg DeRudder

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Ethanol production is good for level measurement and good for the world.....

Ethanol production require a vast amount and variety of process measurement instrumentation as part of the overll automation and control of the plant processes.  For level measurement there are applications throughout the process from monitoring inventories of raw corn to helping to control dryers, to the monitoring of storage vessels containing the finished product.  But recently we have begun to hear in the media a number of comments talking about how bad Ethanol production is and has been.  It has increased the demand for corn and driven food prices up.  Well perhaps in the short term that is true but living out here in the corn belt of Illinois I can tell you that this country has more corn than you can imagine.  And, corn is not the only raw ingredient that Ethanol can be produced from, it is just the most common right now.

The point I want to make is in regards to the impact Ethanol production has on the world supply and cost of fuel.  I point to a study and report recently issued by LECG.  First, LECG (I have no idea what LECG stands for) is a "global expert services" firm.  They do studies and render expert opinions on a number of subjects.  Well, the Renewable Fuels Association had them do an impact study of Ethanol on the cost of crude oil.  That's right.  They answered the question "what would the impact be on crude oil prices today if Ethanol production did not exist?".  Well before I tell you what they found out let me tell you that they reported that the amount of Ethanol produced in the world in 2007 was 17 billion gallons.  The majority of this was produced in the USA and Brazil.  In 2008 it is projected that this production will increase by 20% to 20.4 billion gallons.

There appear to be complexities in calculating the impact of Ethanol on crude oil prices and I don't have the time, nor the patience, to dig into it and report it here for you, but the report by the LECG indicates that crude oil would cost another $35.70 per barrel if it weren't for the production of Ethanol.  Think about the effect of that on the price per gallon of gasoline next time you fill up and next time you drive by a corn field, or next time you hear someone talk down the Ethanol industry.

A complete editorial about the LECG report can be found written by editor Myke Feinman of Bieofuels Journal magazine.  The editorial appears on page 110 of the May/June 2008 issue.

Want to know more about the level measurement and monitoring applications in an Ethanol production operation?  Download this file.  It's a white paper on that subject. Download WhitePaper_EthanolSolutions.pdf   

Joe Lewis

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Scaling Analog Output Displays

During my most recent travels, I found myself at a company that had purchased a Flexar Guided Wave Radar equipped with an analog output (4-20mA). In this case the analog signal is being fed to a programmable digital panel meter (only) and not to a PLC for control purposes. I was dispatched to this facility because the end user reported that the material levels being displayed on the panel meter, as a “percentage full”, was not accurate and it caused an overfilled tank. In this case, the only thing purchased from us was the level sensor. The digital panel meter had been purchased from a local supply company. The panel meter came preconfigured to display zero percent with a 4mA input and 100 percent with a 20mA input.  Sounds like a text book scenario does it not?

Well Bunky, hang on to your hat.  What effects do analog output program parameters (ie. set points) have on a simple installation as described above? The answer to that question could sometimes be multi-faceted. Some questions to ask and consider include, but are not limited to, the following:

1. Is the tank height taller than the probe length?  Usually yes. This may affect set-points of the analog scaling and, more importantly, affect the scaled accuracy. Read on for more on this.

2. Do the 4 and 20mA set-points need to account for the effects of any possibly  existing dead bands?  Not necessarily, but this can be a tricky subject for all involved parties to agree upon. However, when you program your panel meter to represent 100 percent full based upon the tank height (a true percentage) but your probe can not measure the last two feet of level because of a dead band, you will never see 100% on your meter unless the output shifts to an error signal of say 22 or 23mA, in which case you will see more than 100%. The same holds true for the probe bottom. When you keep your probe length short so as to have the minimum stated clearance between the probe and the tank bottom (or some internal obstruction), when you meter initially falls to 4ma, your meter will show zero percent but you still have material in your tank. You just can’t measure remaining material below the bottom of the probe.  This is where adjusting the meter scaling for the 4mA set-point to represent the amount of remaining material in the tank is sometimes desirable, but similar adjustments for the 20mA set-point should also be implemented to the meter so as not to skew the span values in the area that are actually legitimately measured by the probe (the area not in the dead band).

3. What happens to the analog output if the material level enters a dead band?  This depends on sensor functionality, programming, and how the firmware treats an output when the material level can not be seen. However, you need to know this before it happens and so you can educate all persons involved in decision making and operators about probe functionality and what they can and should expect under all operating conditions.

Although in the above example I was talking about a level measurement displayed as a percentage of a full vessel, the same relationships hold true for any unit of measure selected by the decision makers and/or plant operators.

“So, what is the point of all this?”, you ask.      I’m glad you asked.

I get into situations like this all too frequently. To make sure you can avoid the time and effort of having a problem and needing to contact some tech support personnel after you have experienced a problem in your plant, recognize first that you are not needing to "calibrate" the sensor, just scale the output of the sensor to what you want the panel meter to display for you.  Also, make sure you inform the sales person that sold you the level sensor and/or panel meter understands exactly what you expect.  If you want the level sensor supplier to assume a "system" responsibility then buy the panel meter from them as well as the level sensor.  If you don't, then you are definitely on your own except that the level sensor supplier, a good one, will still try to help you.  Finaly, take into consideration the things I mentioned above and contact the salesman for some upfront technical support on integrating the sensor signal into the panel meter if you feel it is needed.  The time for this is before you install the sensor so everything gets up and running quickly and meets your expectations.

Greg DeRudder

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