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Plastics Bin Level Measurement Solution:

Level Detection...Challenges Sensing Lightweight Polystyrene Flake Regrind in a Blending Hopper

Plastics Level SensorSITUATION:
A South Chicago Heights, IL manufacturer of portion packaging, primarily for dairy creamers, has had much difficulty sensing the high level in their blending hopper. The hopper contains polystyrene flake regrind that is very lightweight. They have not had success using proximity switches due to the low dielectric constant of the material and dust build-up. What can be used for point level monitoring with very light materials and in an environment where some dust also exists?

Materials too light for rotary paddle units (paddle may just turn and carve a hole in the material) and too light and dusty for proximity switches are usually problematic. Even capacitance probes with high sensitivity, such as the TrueCap® family from Monitor Technologies, may not be successful. Lightweight materials usually have very low dielectric constants, close to that of air, making sensing by RF capacitance methods difficult if not impractical. What will work on lightweight materials less than 5 or even 3lbs/ft³?

Vibratory Level Sensor in PlasticsSOLUTION:
Many plastic processors have this problem. Those that work with very lightweight materials, even dust, and any “flake” or “regrind” definitely can have this challenge. However, vibratory point level sensors with a single probe design (not tuning forks) tend to work very well in these applications, unless there is the possibility of very heavy build-ups but this isn’t very likely with very light materials. In this example the customer solved their problem of sensing polystyrene flake regrind by using the Model PZP vibratory point level sensor from Monitor Technologies.

The Model PZP uses state-of-the-art piezoelectric and electronic technologies to provide the ability to sense materials as light as 1.5lbs/ft³. The PZP also provides a relay output and is equipped with a universal power supply for AC or DC operation.
The PZP is a proven problem solver even for difficult challenges like very lightweight materials. The PZP is available in a wide range of probe configurations.

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

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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