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RGI - Online moisture measurement with microwaves

When  microwaves penetrate bulk material, the free water molecules contained therein are excited to rotate by the microwave radiation, which in turn slows down the microwaves (phase shift) and significantly weakens it (damping).

This  change in the microwave can be measured (both effects correlate with the water content) and thus used for a very precise determination of the material moisture.

Product specification

Online moisture measurement with microwaves

Description

A  complete measuring system for online moisture measurement, consisting of the microwave modules RGI 8403 and an industrial PC with the evaluation software FANAL W32.

In  most cases, the occupancy on a conveyor belt varies, i.e. bulk density or height change, but the system provides moisture values without recognizing whether they are caused by changing moisture or quantity, which is why it is absolutely necessary to record this varying load during the moisture measurement in order to be able to clearly assign the measured value to the moisture .

The  information about the assignment can e.g. from a belt scale as a 0...4-20 mA signal, but if the delivery rate is not of interest, only a point measurement of the occupancy can be carried out with an ultrasonic range finder.


RGI 8403 
Microwave modules
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FANAL W32
PC evaluation software
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Evaluation

Industrial  computers from RGI
● based on a standard PC
● Connection to other systems (higher-level computers or PCS)

FANAL W32 software
● The menu is easy to understand despite the complicated physical and mathematical task
● Measured values in various forms:
    - graphics
    - different mean values
    - and much more
● Display of all results on the color monitor
● Reading possible over a distance of several meters
● Data can be saved for up to 1 month
● Display in table format or as line graphics
● modern color monitor enables:
    - easy calibration
    - higher accuracy
    - Checkability of various parameters for plausibility

RGI

Measuring principle

Microwaves  belong to the electromagnetic waves that are able to penetrate electrically non-conductive matter.

In  materials composed of dipole molecules, e.g. Water, the molecules are vibrated by the microwaves, losing their energy.

The  loss of energy depends on the amount of water they penetrate and therefore a measure of the water content of the material.

If  the loss is not too great, some of the microwaves will arrive on the opposite side and can be measured there.

The  microwaves not only lose their energy, they are also reflected in the medium they penetrate, i.e. the reflection can also be measured as a measure of the water content of the fabric.

In  the transmission measurement, when the material to be measured is placed between the transmitter and the receiver, the entire material is recorded.

When  it comes to reflection, the microwaves have to travel twice, so the detected layer thickness is smaller. It is also difficult to keep the distance to the measurement constant - an important condition for a reflection measurement.

The  transmission method is therefore more meaningful on a conveyor belt, the most frequently used measuring location.

Technique

b  measuring system consists of a microwave transmitter and a receiver.

Horn  or planar antennas can be used as transmitters and receivers. Since horn antennas are relatively large at the frequency used and do not bundle so well, planar antennas are used here.

Because  the transmission method is preferable in any case, the transmitter is placed under the conveyor belt and the receiver above. A bracket is available for installation, which has the necessary stability and prevents geometric changes.

The  RGI microwave moisture measurement can also be used successfully in various other applications because the measuring section can be attached to pipes, measuring shafts with continuous material or even containers.

Metallic  walls then have to be cut out and replaced by ceramic material or plastic.

The  required information for the strip occupancy can come from an appropriate ultrasonic sensor or from a radiometric belt scale (see RMBW) ​​from the RGI product range and carry out the measured value processing with the moisture measurement as a unit in a computer.

It  is then also possible in a simple way to display the tonnage with the moisture value on a screen and to make it available as process data.

Advantages

● measurement is not influenced by changing pH or conductivity of the measured medium
● the total water content, not just that on the surface, is recorded
● the method is absolutely contactless
● there is no wear of electrodes or caking
● the measurement results are immediately available
● direct process control possible

Possible uses

Almost  all bulk goods can be measured with this method, but there are few exceptions: Problems can arise with materials in which the adhering water is not able to oscillate, for example if it is "trapped" in capillaries, which is why crystal water or ice (does not react like water, but like another solid) cannot be detected.

Some  examples of materials that led to successful measurements: brown and hard coal, sand, wood chips, potato chips, tobacco, seeds, etc.

Because  of the extremely low energy emitted by the transmitter, the microwaves are not able to heat the material to be measured. Approximately one thousand transmitters would be required to bring about a measurable increase in temperature.

Accuracy

There  are the most  experiences with coal of about 0-20 mm grain size.

The  accuracy that can be achieved depends on the precise measurement conditions, e.g. whether it is filter cakes or homogeneous moisture distributions.

An  accuracy of ± 0.5% was determined for coals, but the best results so far have been achieved in sand with ± 0.1%.

For  other measured materials, one can assume ± 0.3% or better, e.g. this value was reached in copper ore.

Risks

The  microwave oven is used to the fact that the boiler room must be closed and the normally existing window is closed by a metal grill.

A  microwave oven, however, has approximately 1 million times the power compared to the humidity transmitter.

Temperature  increases of the material to be measured could never be demonstrated.

For  this reason, precautionary measures are not necessary.

That's what makes RGI products so special

User friendly

● simple, intuitive teaching
● retrofitting
● no contact with the material to be measured
● Measurement independent of:
- medium
- process conditions

Safety and quality

● Maintenance-free because there is no wear
● high operational reliability
● Long-term stable measurement
● Recalibration is not necessary
● Checks before delivery:
- Quality, climate and function

"Made in Germany"

● own development and production in Germany
● Use of high quality materials and components
● Use of proven technology
● Worldwide sales and on-site service by trained personnel

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