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February 2011: SiloPatrol® SE Cable-Based Level Sensor
SiloPatrol® SE SMU equipped with a
self-powered analog output

Silo Patrol Level Sensor

The SiloPatrol® SE cable-based level sensor from Monitor Technologies is available with an Analog 4-20mA self-powered output. This SMU sensor is a standalone transmitter that provides an updated (refreshed) direct analog signal each time a new measurement is made.  Measurements are initiated either automatically as programmed within the sensor electronics or as a direct response to receiving a remotely activated electrical “sound” signal.  This sensor model is equipped with a relay output that can be programmed to activate when a user established level is reached or depleted, upon detection of a sensor error, or when a measurement cycle is in progress.  The sensor can be programmed to hold the last output value, to output <2 mA, or to output >23mA in the event of a sensor failure. Choosing either of the last two error signal choices allows your control system programmer to provide timely error or alarm notification by whatever means is appropriate for your plant operation.

The SiloPatrol SE lowers a weight & cable into the silo until it contacts the material surface. Upon contact the weight & cable system is immediately retracted and the measurement is fed to the plant control system or operator interface. The sensor is also equipped with a simple electrical lockout feature for those applications where measuring during fill is not desirable. These sensors are easy to install and are also virtually maintenance free, requiring only a periodic inspection usually once or twice per year.

This system also increases plant safety by making it unnecessary for personnel to climb silos on regular intervals in order to take measurements of the material level. For more information, please visit or call 1-800-601-5953 / 1-630-365-9403.

For more information please visit:

Monitor Technologies LLC, located in Elburn, Illinois, is a leading manufacturer of level measurement instrumentation, solids flow indicators, particle emission monitors and aeration devices for the worldwide powder and bulk solids markets. The experience and market knowledge gained over 50 years of business has earned Monitor a reputation for providing high quality and reliable product solutions backed with trusted customer service. For more information please visit


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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