Typical Applications:
In-line moisture sensors can be used for most powders and bulk solids processes that incorporate conveyor belts, screw conveyors, pipes, chutes etc. (See image below)
Common target materials include:
Cement, Sand, Aggregates, Coal, Feed and Grain, Cereal, Malt, Flour, Sugar, Spices, Potato products, Dried Food / Products, Wood Shavings, Chemicals / Fertilizers, Powder, Pigments, Plastic granules and more.
Installation Options:
HumiCore moisture sensor in a screw conveyor application
Application Example:
The company felt that an in-line (on-line) moisture measurement sensor would help them achieve their goals. The moisture monitoring of the sand would assist them in two important ways:
The company did some research and decided to use the HumiCoreTM PRO in-line (on-line) moisture measurement system. Before the sensor was installed, the company and sensor manufacturer collaborated to determine the optimal location to place the sensor. The moisture sensor was installed immediately following the dryer using a sled to glide across the surface of the sand. At this point, the sand is being conveyed to the size-sorting screen. If the sensor detects a higher level of moisture in the material than desired, an alarm is sent to the control room. Then a chute can divert the sand back to the dryer before it is re-sent through to the sorting screen. Using an optional DIN-Rail transmitter, the company was able to have the output signal of the moisture sensor integrate easily with their other control functions. The HumiCore system has been successfully working as anticipated and the company is very pleased with the results.
HumiCore moisture sensor mounted on a sled in a silica sand conveyor application
HumiCore PRO sensor and transmitter
Technology Review:
Continuous in-line moisture measurement sensors used for process monitoring of product moisture in solids and emulsions applications are usually based off of a few common technologies. These technologies include near infrared (NIR), high frequency field and microwave. The HumiCore™ Pro moisture sensor, chosen by the example company, uses a circuitry principle that is centered around an electrical high frequency field. This is based on technology that has been developed and proven to be successful over several years.
There are several benefits of high frequency field technology including:
To locate an International sales distributor, please visit:
https://www.monitortech.com/locator_intl.shtml
DuraVibeTM Vibratory Level Sensors
Vibratory point level sensors or probes are great products for powder and bulk solids applications where the material being sensed has a very low dielectric constant that might be lower than an RF Capacitance probe could detect. They are also good alternatives for rotary paddle bin indicators in application with extremely low bulk density values. Expanded poly-styrene beads have a bulk density that is typically less than 2 lbs/ft3 (.032g/cm3). Paddle type sensors and especially high level paddle type sensors would very likely cavitate when covered with material this light and give no indication that material is indeed present.
What if we have an application for a bin whose material frequently changes and we were using a rotary paddle bin indicator? If the bulk density decreases, at some point the paddle being used will start to cavitate and a paddle with a higher surface area (increasing the effective sensitivity) would need to be installed to allow the paddle type sensor to regain functionality. There will be a lower limit of bulk density vs. area of the paddle that once reached will ultimately render the paddle type sensor useless for the application in question. If an RF Capacitance probe is being used in silos, hoppers or bins and the material is changed to something with a radically different dielectric constant, probe re-calibration might be required. This is where a vibratory probe is a great choice because there is no calibration per se. Many vibratory probes on the market do have a general sensitivity setting that can be changed but that is an adjustment the rarely needs to be set differently than the factory default.
The main downside of a vibratory probe is that it is generally more expensive than a rotary paddle or RF Capacitance type of sensor. Another negative feature of a vibratory probe, and main point of this article, is that models that are high in sensitivity and able to detect materials with very low bulk densities are typically not as physically strong in comparison to other point level technologies. So when we use a vibratory probe, we must strictly adhere to the manufacturer's installation guidelines.
According to a conversion website I frequent:
150 Newtons = 33.7 pound-force.
500 Newtons = 112.4 pound-force.
1000 Newtons = 224.8 pound-force.
"So what?” you exclaim.
One of the most common reasons for vibratory probe failure is from the probe having been subjected to forces beyond their design limitations. Such a condition can actually bend the probe rendering it useless. Other modes of failure include broken components within the probe housing or within the probe element if it is a rod type or diamond shaped design.
Below are examples of parameters for vibratory probes.
MODEL PZP PROBE LIMITS
OK, here come the Newtons. Monitor's DuraVibeTM Model PZP probe has two separate force limitations. The probe must be installed such that the narrow edge (knife edge if you will) of the probe is always pointing up. The PZP can withstand 1000 Newtons max in this plane but will only withstand a maximum force of 150 Newtons along and perpendicular to the axis on the wide side of the probe. Our DuraVibeTM Model VibraRodTM probe is constructed using a hollow tube that is cylindrical shape and is rated at 450 Newtons max in any plane along and perpendicular to the axis.
Generally speaking, either probe should be shielded from direct impact from material falling directly on the probe during the filling process depending upon material characteristics. There are suggestions for doing so in our Installation & Operation Bulletins for these products.
So, when you need or want to use a vibratory probe, be mindful of all forces the probe will be exposed to during fill and also when material is being drawn out. How and where the probe is mounted to the vessel will have a direct influence on the amount of force the probe is subjected to when the material contained in the vessel is in a dynamic state. Mass flow silos and hoppers will produce more force against the probe than its funnel flow counterpart would exhibit. Properly placed baffles will correct this problem. Also determine if there will be any significant side or lateral horizontal loads that either require silo modification or require the selection of a different style of probe so ensure that maximum force specifications are never exceeded. If you find yourself needing or desiring a vibratory probe and you have determined a need to install protective baffles or shields but you are unable to install them, you should consider using a top mounted cable extension model or a rigid pipe extension model. A cable extended probe will allow the actual sensing portion of the probe to hang freely at the desired point of material detection without exceeding specified lateral force limitations. See examples below.
Model PZP with cable extension
Now if this seemed all too gloomy for you, relax. We have many successful applications in materials with bulk densities as high as 100 lbs/ft3. You just need to think about the application and install the probe in such a manner that its limitations are not exceeded. When in doubt, give our Technical Support department a call at 800-766-6486 or 630-365-9403 for advice and guidance. We are here to assist you by providing practical solutions on and at every level we can.
Greg DeRudder
Product Manager / Director of Sales
Monitor Technologies LLC
[email protected]
www.monitortech.com
© 2010, 2017. All rights reserved.
Bulk materials, especially powders, stored in vessels can settle (pack) and tend not to flow well through a process system.
Monitor Technologies’ offers some bin aeration devices that are simple solutions to maintain the flow of dry bulk powders and granular solids in storage vessels. Monitor’s booted Evasser aerator is compact, durable and capable of aerating / fluidizing many types of bulk powders and granular solids in bins, hoppers and silos. It operates by constantly presenting air to the mass of the stored material. The Evasser features no moving parts, no filters to change, and no loud noise or damaging vibrations. The Evasser bin aerator is also available with a convenient external mounting plate.
Monitor’s Rectangular Air Pad operates by continuously introducing air into the body of the dry powder to maintain fluid-like characteristics. Highlights of the Air Pad include rugged construction, low cost, minimal maintenance, easy to install and adapts to almost any bin configuration.
For more information visit www.monitortech.com or contact Monitor's Technical/Application Support Team at Tel.: 1-630-365-9403.
Monitor's Technical Support can assist in suggesting a system that will fit your application needs. Here is a link to an aeration application form that can be completed and submitted to [email protected] for assistance / suggestions... http://www.monitortech.com/appquest/916A.shtml
SafePoint® Fail-Safe Rotary Paddle Level Sensor
A rotary paddle style unit is a very common sensor used to indicate high, intermediate and low levels in vessels. The main reasons for this are that these sensors are affordable, durable and reliable for a variety of powders and bulk solids. A good way to ensure that this type of sensor will be reliable for your application is to make sure that you are using the correct paddle assembly for your target material. Factors like different material densities, particle sizes, flow characteristics and sensor mounting may require specific paddles to provide optimum performance. Monitor Technologies offers a variety of interchangeable paddle assemblies for the Model KA/KAX and SafePoint® level sensors to meet the needs of a wide variety of materials / applications.
Click here to view a guide that can assist with selecting the right paddle for your application. In addition you can contact Monitor’s Application Engineers to discuss the best option for your needs.
Overview of Available Paddle Assemblies
The WirelessEZ Communication Interface (radio modem) is a practical option when hard-wiring is not feasible (example: to cross a river, to span a large facility, property is divided by a railroad track, etc.) It provides wireless communication for Monitor Technologies' SiloPatrol® SE (SMU) plumb bob style sensor or Flexar® guided wave radar sensor or customer-supplied equipment utilizing half-duplex RS-485 communications (please consult a Monitor Technologies application Engineer).
The WirelessEZ Communication Interface is suitable for wire-replacement applications when wired half-duplex RS-485 communication is not practical.
The WirelessEZ uses proven frequency-hopping spread spectrum technology, operating in the 900MHz band, to communicate between two points. The 900MHz band is a FCC license-free band and offers greater transmission distances, better signal transmission through obstructions and lower signal loss than other available higher frequency bands. WirelessEZ Communication Interface can be utilized in numerous applications, even with multiple sensor networks and over 100 sensors.
For more details please visit: http://www.monitortech.com/product_c_c_wireless.shtml
Models PAC-30U and PDC-30 proximity level switches are used to detect the presence or absence of many materials including low-dielectric substances. The optional mounting well provides easy sensor removal, if needed, without having to wait for your hopper, bin or tank to become empty. These compact capacitance-style level sensors are excellent for those hard to reach and tight areas. Additional features include easy installation and calibration, adjustable sensing distances, fully electronic (no moving parts) and LED status indicator.
Monitor Technologiesoffers two different models of solid state, capacitance-style proximity switches. The PAC-30U is an AC operated unit that is a universal, switch selectable for either normally open or normally closed operation. The PDC-30 is monitor’s DC operated unit and is available in either PNP or NPN configurations, each of which can be wired in a normally open or normally closed operation mode. Please visit www.monitortech.com.
Rectangular Air Pad, Evasser, Flo-Pad (Pictured Left to Right)
There are a variety of bin aeration devices available to maintain the flow of dry bulk powders and granular solids in storage vessels. Monitor’s Rectangular Air Pad operates by continuously introducing air into the body of the dry powder to maintain fluid-like characteristics. Highlights of the Air Pad include rugged construction, low cost, minimal maintenance, easy to install and adapts to almost any bin configuration.
Monitor’s booted Evasser aerator is compact, durable and capable of aerating / fluidizing many types of bulk powders and granular solids in bins, hoppers and silos. It operates by constantly presenting air to the mass of the stored material. The Evasser features no moving parts, no filters to change, and no loud noise or damaging vibrations. The Evasser bin aerator is also available with a convenient external mounting plate.
The Flo-Pad aeration system uses multiple Evasser aerators mounted on a single air chamber inside the vessel to introduce air and promote flow, even in some more difficult stored powder / granular solid applications.
Monitor's Technical Support can assist in suggesting a system that will fit your application needs. Here is a link to an aeration application form that can be completed and subitted for assistance / suggestions. http://www.monitortech.com/appquest/916A.shtml
A company that provides powder coated metal products "dipped" the metal parts into a pan / bin of highly fluidized powder. Then the metal parts were heated to adhere or "bake on" the powder to the metal.
They were looking to solve two situations. First, they needed to make sure that the powder in the pan / bin would stay highly fluidized in order for the metal pieces to be evenly coated. Secondly, they were looking for a way to be notified when the powder in the pan / bin was getting low and needed to be replenished.
For the aeration situation, they would be able to install multiple Monitor rectangular air pads on the pan / bin that introduced enough air to keep the powder "boiling and bubbling". The powder would now stay highly fluidized.
For the level indication situation, a Monitor PZP vibratory-style level sensor was recommended. The PZP is designed for accurate detection of lighter and fluidized materials. The PZP would be installed at the point on the pan were the company would like to replenish the material. When the PZP level sensor no longer detected material at that point, it would provide a signal to the operator so that the pan could be replenished.
Monitor Technologies’ PZP vibratory-style bin level
indicator has a diamond shaped probe and is ideal for materials as light as 1.25
lb/ft3 (20 kg/m3) including powders, expanded polystyrene beads, fumed silica and more. The PZP also works well in situations where material
properties or environmental conditions are variable.