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Continuous Level Measurement of Extremely Lightweight Specialty Materials

“I can’t find a technology to measure the level of my finished product. It is extremely lightweight, less than 5lbs/ft³, and nothing seems to work”.

Very lightweight materials are definite challenges for continuous level measurement technology. There is so much air that the dielectric is very low and sound absorption is high. This means that guided wave radar, through-air radar, ultrasonic and RF capacitance technologies are all out of the question. 3M in Cottage Grove, MN had this exact problem. They manufacture a highly proprietary and specialized packaging material. They needed continuous level monitoring of their raw material and finished goods bins. The raw materials were not challenging per se, but the finished product was extremely lightweight, less than 5lbs/ft³! 3M needed a solution.

The Monitor Technologies SiloPatrol® Inventory Monitoring System is a smart weight & cable based sensor system. This state-of-the-art weight & cable system is a proven problem solver, but will it work effectively on material less than 5lbs/ft³? Yes! The local Monitor representative arranged a demonstration and a unit was temporarily mounted on a skid and then placed on top of a large box of the material. It worked perfectly. The design of the sensor weight (an inverted cone design) and the electronics/mechanical design of the sensor allowed the unit to detect the surface of this lightweight material without sinking into the material.

The SiloPatrol system is now used on the raw and finished goods silos. According to the customer, “the SiloPatrol system is one of the few devices we have that operates flawlessly”. The sensors have been installed since the late 1990’s and the customer still has their initial purchase of spare replacement parts.

Give Monitor Technologies a call and let us put our creative solutions to work for you!


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Spotlight: RF Capacitance Level Sensor
TrueCap Level SensorsTrueCap Light  
TrueCap® MK-2
Advanced RF Capacitance Level Probe

The TrueCap® Model MK-2 RF Capacitance point level probe is designed to provide a superior and stable sensitivity threshold making it suitable for a variety of powder / bulk solids and some liquid or slurry applications.

Advanced features of the Model MK-2 include:
> Automatic immunity to material build-up on the probe by its driven shield design
> Push-button calibration
> Enhanced temperature compensation
> Maximized reliability via smart sensing algorithms like “self-validating” fail-safe protection
> Visible status LED on ordinary location units
> Versatility through a variety of configuration options including: hazardous location version, split architecture design, quick-connect process connection, stub probe, cable extensions, solid extensions, Nylon® probes, Ryton® - equiv. probes, etc.

A practical application for the TrueCap would be to use this level sensor where a residual material build-up on a different sensor would cause a false material level indication.

Principle of Operation for the TrueCap RF Capacitance Level Probe:
The vessel wall and the active probe element establish an impedance reference between each other when exposed to air which has a dielectric constant of 1. When materials with a dielectric constant greater than 1 are in close proximity to the probe, the impedance of the sensing field between the sensor and the vessel wall will change. Once the amount of change exceeds a threshold that was electronically determined during the calibration process, an output relay will either be energized or de-energized depending upon the position of the fail-safe selector on the probe’s electronic circuit board. A change of as little as .5 pico-farad is all that is necessary for the probe to sense the presence of material.

Click here for more information on the TrueCap MK-2 Level Sensor or contact Monitor Technologies LLC at
Tel.: 800-766-6486 in the USA and
Tel.: 630-365-9403 worldwide.


>>Download TrueCap Product Bulletin #413

>>Click here to learn more about other Point Level Switches from Monitor Technologies


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