RF Capacitance – MK2

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 (Comparing the model MK-2 and MK-2e)

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-2 RF capacitance point level sensor is a proven problem solver used to ensure maximum performance and reliability, minimizing downtime of operations.

	Microcontroller based for maximum reliability & performance
	Push-button calibration, sensitivity selection & self-test
	Automatic temperature compensation for unmatched calibration stability
	Superior 0.5 pF sensitivity ensures reliability
	Build-up immunity helps eliminate false signals
	High intensity LED indicating light (Ordinary location sensors only)
	Universal power supply minimizes versions
	Available hazardous location approvals with intrinsic safety

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

Global Flour Processor Uses Flexar® Guided Wave Radar

A large global flour processor and food products company recently began using the Flexar® guided wave radar in a total of eighteen (18) silos and bins to manage their finished product inventory.  Readings from these continuous level sensors is reported as being reliable and accurate, even during pneumatic filling, contrary to their previous measuring system.  A previous non-performing ultrasonic system was replaced by the Flexar level sensors.  Flexar guided wave radar level sensors were chosen as the best for pneumatically filled dust laden flour silos.

Eight (8) Flexar level sensors are installed in load-out silos that fill bulk trucks with processed and finished flour.  These silos are 12ft in diameter and 35ft tall.  The finished flour is pneumatically conveyed into these silos.  During filling the internal environment of the silos is very dusty and turbulent.  The finished flour in these silos is used for loading bulk transport trucks for distribution.  In addition, ten (10) Flexar level sensors are installed in 40ft high bins that contain bran.  This material is also sent by bulk transport to end users.

All of the Flexar level sensors are equipped with an RS485 digital communications output that is connected to a PC with a graphical user interface for inventory management purposes.  Monitor’s SiloTrack™ inventory management software is used by the facility to monitor and manage material inventories of both the finished flour and the bran.  SiloTrack allows for multiple user viewing and data access via LAN and this is how the facility will be using the software that provides a flexible, graphical user interface, alarms, report generation and history analysis functions.

Guided wave radar is especially well suited to level measurement applications of dusty powder materials even when measuring during pneumatic filling.  Flexar guided wave radar utilizes TDR (time domain reflectometry) technology.  Radar pulses are continuously transmitted down the sensor’s probe and guided to the material surface where they are reflected back to the electronics along the wave guide.  The time-of-flight of the pulses is measured and directly related to the distance to the material surface and its level.

>>Click here for more information about Flexar guided wave radar continuous level measurement sensors.
>>Download Product Bulletin 353A
>>Click here to visit our Flexar Website