RF CAPACITANCE – MK2E

BULLETIN 413

TrueCap® RF capacitance sensors offer cost-effective point level monitoring with reliability you can count on. Monitor’s complete line, which features models MK-2 and MK-2e, provides you with the most affordable solution for your application. Monitor’s RF capacitance probes are designed to provide a high level of sensitivity, stability and durability for powder and bulk solids applications, as well as liquid and slurry applications. Monitor’s two-year warranty stands behind every TrueCap sensor.

Principle of Operation

A radio frequency is applied to the probe and is continually analyzed to determine the influence caused by the surrounding environment. As material contacts the probe, the radio frequency shifts indicating an increase in capacitance (C). The active probe of the unit and the vessel’s wall make up the two plates (A=area) of a capacitor which are separated by a fixed distance (d). The probe’s insulator and surrounding air provide the dielectric material (with dielectric constant “K”). As the air (K=1.0) is displaced with any other material (K > 1.0), the capacitance effect (C) is enhanced, thereby changing the application’s impedance. This influence is measured within the circuitry and compared to a reference established by the sensitivity setting. The setting determines how much influence must be present before the output changes.

The driven shield section of the probe enables the circuitry to ignore product build-up on the probe that would otherwise cause false sensing. The driven shield is activated with the same radio frequency potential as the sensing probe. Since current can not flow between identical potentials, the driven shield blocks current flow from the active probe to the vessel wall through the material build-up, thereby eliminating the sensing of the material build-up.

Applications

TrueCap® RF capacitance point level sensors are versatile devices providing high and low level readings in bins, silos, tanks, hoppers, and other vessels. TrueCap’s superior sensitivity range allows users to properly adjust units to meet the needs of a wide variety of applications. Whether your application is for a powder, liquid, granular solid, or viscous material, the TrueCap product line offers the right solution.

Model Selection

Monitor offers the market an unmatched selection of RF Capacitance point level sensors. Several parameters should be considered when selecting the proper TrueCap® RF capacitance point level sensor.

EASE OF CALIBRATION
Many applications are well served by the manual calibration of the MK-2e, but only the MK-2 offers the extraordinary convenience of push-button calibration, sensitivity and self-test.

CALIBRATION LOCATION
Some applications place probes in locations which are difficult to access. The Remote Calibration Module (MK-2 only) provides all push-button functions from a location up to 1,000 feet (305 m) away from the probe. Also, the split architecture versions of both the MK-2 and MK-2e provide remote calibration 12 feet (3.7 m) or more away from the probe.

VARYING TEMPERATURES
It is important that the calibration of a probe remains stable during swings in the process and ambient temperatures. The MK-2 automatically adjusts its calibration to account for temperature changes providing maximum reliability.

CHANGING CONTENTS/CHARACTERISTICS
TrueCap sensors can be calibrated to the material with the lowest dielectric constant (usually the driest material) in order to sense all products which could enter the bin. However, sometimes the need for re-calibration is unavoidable, making the MK-2 with push-button calibration and an available remote calibration module the best choice.

HEAVY MATERIALS & TIGHT AREAS
Some applications require compact, sturdy probes for heavy materials or confined spaces. The MK-2 and MK-2e offer a stub probe for extra durability for heavy products and a compact design for tight areas. Both models also use heavy duty 3/8 inch (9.5 mm) diameter probes.

SOLIDS
All TrueCap sensors can sense solid materials, but be careful to also look at all application parameters.

MATERIAL COATING/BUILD-UP
Many liquids, slurries and sticky bulk solids tend to cling to probes. Product build-up immunity through a driven shield design is a must. The MK-2 and MK-2e provide product build-up immunity and can typically be used with these materials.

HIGH VIBRATION
When locating sensors near vibrators, bin dischargers or other vibrating equipment, the split architecture version is recommended.

UNIVERSAL POWER SUPPLY
Minimizing the number of variations can maximize value for OEMs and product resellers. The MK-2 is the only TrueCap sensor that provides this capability.

NEED FOR VISUAL INDICATION
Both the MK-2 and the MK-2e are provided with a high intensity LED indicator on the housing (Ordinary location integral sensors only).

HAZARDOUS LOCATIONS
The MK-2 and MK-2e are available approved for Class I and Class II hazardous locations. See “Specifications” for details.

HIGH TEMPERATURE
For applications up to 450°F, (232°C) the MK-2 and MK-2e offer stainless steel mounting connections which act as thermal barriers and a split architecture version which completely removes the electronics from the process.

LARGE PARTICLES
Large particles can leave air gaps which could lead to inaccurate readings. However, smaller particles and fines usually fill in the gaps.

Features

The TrueCap® Model MK-2e RF capacitance point level sensor is a reliable sensor and is a standard for many OEMs and end users requiring versatility and lower cost.

	Superior 0.5 pF sensitivity ensures reliability
	Build-up immunity helps eliminate false signals
	High intensity LED indicating light (Ordinary location integral sensors only)
	Available hazardous location approvals with intrinsic safety
	Simple 2-step manual calibration
	Economical

Options

Accessories

Probe Variations

Dimensions are shown in inches with millimeter equivalent in brackets.

STANDARD PROBE The most commonly used probe variation, the standard probe performs reliably in many different applications. The standard probe is available with either a 1-1/4” NPT, 1-1/2” BSPT* or 3/4” NPT process connection. *Unit with 1-1/2” BSPT connection is provided with M20 cable glands.
STUB PROBE Usually used in tight spaces, or in applications with heavy material, the stub probe is a shorter version of the stub probe. The stub probe is available with either a 1-1/4” NPT, 1-1/2” BSPT* or 3/4” NPT process connection. *Unit with 1-1/2” BSPT connection is provided with M20 cable glands.
CABLE EXTENSION PROBE The cable extension probe can extend the sensing point up to 50 feet (15 m) beneath the mounting point. It should be noted that the build-up immunity, however, is not extended with the cable version. Use the pipe extension probe in those applications requiring build-up immunity. A 1-1/4” NPT, 1-1/2” BSPT* or 3/4” NPT process connection is available. *Unit with 1-1/2” BSPT connection is provided with M20 cable glands.
PIPE EXTENSION/LAGGED HOUSING The pipe extension probe extends the sensing point and build-up immunity up to 12 feet (3.6 m) down into the bin. The lagged housing version “Lags” the housing up to 24 inches (610 mm) away from the mounting point for high temperature applications and/or vessels with external insulation.

Specifications

* Influenced by mounting, material thermal conductivity and ambient temperature.
** Hazardous location approvals on units with Pipe Extension or Lagged Probes with integral electronics/probe are CSA(US/C) Class II Groups E, F & G (SS version ONLY. Hazardous location approvals are not available on the galvanized version). Hazardous location approvals for Split Architecture remote electronics are Class II, Groups E, F & G. All probe versions, except the galvanized version of the pipe extension or lagged probe unit, are Class I Groups C & D, Class II Groups E, F & G and Intrinsically Safe.

Probe Specifications

Ryton® - Trademark of Phillips Chemical Co.
Teflon® - Trademark of DuPont Chemical Co.

Warranty

Monitor Technologies LLC warrants each TrueCap® RF capacitance sensor it manufactures to be free from defects in material and workmanship under normal use and service for two (2) years from the date of purchase. The purchaser must notify Monitor of any defects within the warranty period, return the product intact, and prepay transportation charges. The obligation of Monitor Technologies LLC under this warranty is limited to repair or replacement at its factory. This warranty does not apply to any product which is repaired or altered outside of Monitor Technologies’ factory, or which has been subject to misuse, negligence, accident, incorrect wiring by others, or improper installation.

413A.9.0407

SiloPatrol^® SE
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 from 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.

For more information on the SiloPatrol SE click here or contact Monitor Technologies LLC at 800-766-6486 in the USA and 630-365-9403 worldwide.

>>Click here for more information about SiloPatrol SE from Monitor Technologies.
>>Download Product Bulletin 343A