English
 Supplier sign in
Home
STAY INFORMED
Subscribe to our monthly newsletter.
Your email address will never be disclosed to any third party.
Read our privacy notice.

       

Specialist article
23.08.2018  |  34219x
Share this item

How does the capacitive measuring principle work?

The function of a moisture sensors using a capacitive measuring principle is explained.

There are plenty of different measuring methods to determine the residual moisture of material such as bulk solids. Now we are focusing on the capacitive functional principle. Inter alia it finds its use in in-line moisture measurement (directly integrated within a working process).
It can be classified into two methods of moisture measurement, direct and indirect.

Direct measurement

Direct measuring procedures are e.g. the Karl-Fischer-Tritation or drying out material (loss of water by using a drying cabinet, probably the most often used method).

Indirect measurement

Moisture sensors and systems belong to the indirect moisture measuring techniques as they allow conclusion concerning the water content by using for example the capacitive moisture measuring principle. Further possible measurements work with microwave, infrared or conductance methods. The main criteria is that these procedures do not detect the residual moisture of the bulk solids directly. Rather they use their physical characteristics and how they change after the material has been dehydrated or moisturized. That is the reason why it is necessary to calibrate the sensor to the individual material.
Online moisture measuring sensor for determining the watercontent of bulk solids like biomass, sawdust, wood chips, pellets, wood shavings, wood boards, grain, coffe beans, cocoa beans, salt, sugar, gypsum, sand, concrete and many more!
Online moisture measuring sensor for determining the watercontent of bulk solids like biomass, sawdust, wood chips, pellets, wood shavings, wood boards, grain, coffe beans, cocoa beans, salt, sugar, gypsum, sand, concrete and many more!

Capacitive measuring principle


The capacitive measuring principle is based on the working principle of a capacitor. A capacitor creates an electric field between two conductive plates when the voltage is applied.
Capacitance (C) names the ability of a capacitor to accumulate electric charging (depending on the voltage). It is the effect of the combination of the area of overlap (A) on the two plates (in square meters), “d” the separation between the plates (in meters) and “ɛ” the relative permittivity (a.k.a. the dielectric constant) of the material.

Capacitance is proportional to the area of overlap but inversely proportional to the separation between the conducting sheets. The bigger the area of overlap is and the closer the sheets are to each other, the greater is the capacitance.

The dielectric constant depends on the insulation characteristics of the dielectric medium (bulk solids) within an electric field. It indicates how permeable the material is for electrical fields.

Graphic about the working principle of a capacitive moisture measuring sensor. Moisture measurements can be used for detecting the water content of bulk solids like sawdust, pellets, wood chips, coffee beans, cocoa beans, salt, grain, gypsum, sand, concre
Graphic about the working principle of a capacitive moisture measuring sensor. Moisture measurements can be used for detecting the water content of bulk solids like sawdust, pellets, wood chips, coffee beans, cocoa beans, salt, grain, gypsum, sand, concre

The distance of the conducting sheets (d) and the size of the plates themselves are always kept constant to a capacitive sensor. So the changing of the relative permittivity of the material allows a conclusion relating to the water content because it is the only parameter that is changing.

As you can see on the image below water has a dielectric constant of 80 (based on standard ambient conditions). Many carrier materials have a relative permittivity between 2 and 10. This great difference allows this capacitive moisture measuring technology to get a high response regarding the water content of the measured materials (bulk solids).
Graphic about the working principle of a capacitive moisture measuring sensor. Moisture measurements can be used for detecting the water content of bulk solids like sawdust, pellets, wood chips, coffee beans, cocoa beans, salt, grain, gypsum, sand, concre
Graphic about the working principle of a capacitive moisture measuring sensor. Moisture measurements can be used for detecting the water content of bulk solids like sawdust, pellets, wood chips, coffee beans, cocoa beans, salt, grain, gypsum, sand, concre

Vacuum: εr = 1; Measuring medium: εr = 2 to 10; Water: εr = 80

The capacitive moisture measuring method is very adaptable and can be used for many applications. So the water content of various material like sawdust, wood chips, cocoa beans, gypsum and many others can be determined throughout the complete moisture range.

On the front of a capacitive moisture sensor there is a stray field capacitor mainly protected by a robust ceramic plate (or rubber/teflon for rough areas) to generate an electrical field. The material that should be measured has to pass constantly this electrical field (e.g. sand on a conveyor belt). That affects the stray field capacitor. After the sensor has been calibrated to the material the measuring signal can be transmitted via analogue norm signal (4…20mA/0…10V) or by Profibus DP to a PLC or another control system. The reference value for calibration use is determined by dehydration process with a moisture laboratory device (moisture lab analyzer).

Company information

More items

ACO AMMS moisture sensor Moisture measurement for coffeebeans in jute sacks
ACO AMMS moisture sensor
Moisture measurement for coffeebeans in jute sacks The AMMS sensor with its integrated microprocessor establishes a transition between the DMMS system and the analog moisture measuring sensor MMS. Besides a power supply, this sensor only needs a display or a PLC which is waiting for its measuring value. The AMMS sensor has been designed for applications which do not need a multi-pieced system but benefit of a precise on-line calibration that is able to compensate the influences of the installation. It’s also possible to calibrate the AMMS sensor directly by an integrated rotary encoder. This work actually takes place before the sensor has been installed. Measurable materials: biomass, pellets, wood chips, wood shavings, wood boards, firewood, coffee beans, cocoa beans, salt, paper, grain, corn, wheat, concrete, sand, ash, recycling glass, plastic, peat and much more! Don’t you know if your material is measurable? We examine your material in our in-house laboratory. Please do not hesitate to contact us!
12.09.2017  |  16816x  |  Product news  |   | 
SFM4 compaction unit for moisture measuring in sludge How moisture is measured in sludge - easily explained!
SFM4 compaction unit for moisture measuring in sludge
How moisture is measured in sludge - easily explained! Moisture measurement for sludge with individual developed screw compaction unit from ACO. The mounted moisture sensor is determining the water content of the waste sludge. The signal of the moisture sensor is used for managing the drying process.
07.08.2017  |  15433x  |  Product news  |   | 
Moisture sensors for coffee beans Inline Moisture Measurement in Copal C2 Bags Handling Line
Moisture sensors for coffee beans
Inline Moisture Measurement in Copal C2 Bags Handling Line Realization of continual quality monitoring of coffee beans by implementing a moisture measurment in the automated bags loading- and unloading system ”Copal - C2 bags handling line”. Four moisture sensors detect the water content of coffee beans instantly. Immediate outward transfer of the jute sacks with high moisture values. Intention of realizing a Load- and Unloading System with integrated moisture sensors Nestlé, the largest food company in the world and leader in the field of nutrition, health & wellness has given a new input on their moto “Good food, good life”. While Nestlé has plants all over the world and in almost every country, they feel highly responsible for the welfare and wellbeing of their employees. Creating Shared Value (CSV) is not something that is not meant to look good for their stockholders, it’s a responsibility they take very seriously. One of the top priorities is keeping the people healthy and save. For this reason they
12.06.2017  |  18841x  |  Product news  |   | 
Hygienic application for ACO moisture measuring systems ACO moisture measuring instruments: food industry and pharma industry
Hygienic application for ACO moisture measuring systems
ACO moisture measuring instruments: food industry and pharma industry ACO-Automation Components shows a hygienic solution for using their moisture measurement systems in the food and pharma industry. An ACO moisture measuring sensor determines the water content/residual moisture of bulk material through a food approval plastic plate. This installation kit has been specially developed for measuring bulk goods in screw conveyors. This method prevents a direct contact between the moisture measurement sensor and the bulk solids. https://www.acoweb.de/en/produkte
30.09.2016  |  18428x  |  Product news  | 

Related categories

PORTALS
BulkSolids-Portal Schuettgut-Portal Recycling-Portal
Related
Bulkgids.nl
SIGN UP FOR OUR NEWSLETTER
Newsletter archive
Service and contact
ContactDisclaimerPrivacyAdvertising
FOLLOW US
Linked