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October 2008: SiloPatrol® SE


Silo Patrol in Coal Level Application

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 feed with steam and the steam created by boilers that are fired by … yep, coal.  But coal as it comes from the mining operations 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 the demand for it to be fed to the burners.  The inventory of coal powder in these silos needs to be monitored to allow for efficient operation of the power plant.

So, how do we monitor the inventory 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 fro Monitor Technologies LLC, the SiloPatrol® SE.

Anhui Tongling power plant in Anhui province in China had tried almost ever technology possible to get a reliable level measurement in their 5 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 the SiloPatrol SE smart cable-based inventory monitoring system that the power plant personnel found a reliable solution.

Mr. William Yuan, sales manager for Beijing Conasen indicates that the power plant tried many major brands of ultrasonic, radar, and other technologies but that due to good relations with the Tongling plant personnel he was able to sell three SiloPatrol SE model SMU sensors and an HMI operator interface to them.  The units were installed by plant personnel.  Because of the heavy amount of coal dust in the silos an air purge using dry compressed air was used.  The SiloPatrol sensor incorporates the patent-pending use of Hall-effect sensor technology, a split-compartment enclosure, microcontroller, redundant optics and many other valuable features and technology to ensure reliable measurement even in challenging dust applications like coal powder.

The SiloPatrol SE system has been working reliably and the plant has since purchased two additional sensors and connected them into the same HMI operator interface.  This same sensor technology is working reliably at other coal-fired power stations in China as well.

Monitor Technologies LLC is a pioneering supplier of level measurement instrumentation, solids flow monitors, 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. Monitor is located in Elburn Illinois.
For more information please visit, and our blog at You can also contact Monitor Technologies at 1-800-766-6486 in the USA or 1-630-365-9403.




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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