What is moisture measurement? A clear explanation of typical measurement methods and how to choose the right one.

What we want to know from moisture measurement is "how much water is contained?"

The purpose of moisture measurement is to determine how much water is contained in a given object. This can involve measuring the amount moisture directly, or it can be expressed as a percentage of the object's total water content, such as a water content ratio.

We don't measure all moisture content directly using the same method.

moisture measurement can be done not only by directly extracting and measuring the water in the object, but also by utilizing methods that take advantage of changes in mass, chemical reactions, electrical properties, and optical properties caused by moisture.

The method varies depending on the object and purpose of measurement.

For example, the required measurement methods and operating conditions differ depending on whether you want to precisely determine a standard moisture content or continuously monitor changes in moisture content on a manufacturing line.

Heat drying method/drying loss method

This method involves heating and drying a sample, and then determining moisture from the change in mass before and after drying. Its concept is easy to understand, and it is used for measuring moisture of solid samples.

On the other hand, it is necessary to set conditions such as drying temperature and drying time. Also, if volatile constituent other than water are present, changes in mass other than moisture may affect the measurement results.

Karl Fischer method

This method utilizes a chemical reaction between water and a reagent to quantify moisture. It can be used to measure trace amounts of moisture and is applicable to various samples, including liquids and solids.

On the other hand, this method may require sample collection, pretreatment, and handling of reagents, so its purpose differs from methods that continuously measure the product as it flows through the manufacturing line.

Electrical resistance type

This method estimates moisture by utilizing the change in electrical resistance caused by moisture. While there are relatively simple measurement methods available, they can be affected by the electrical properties of the material and conductive substances.

Capacitive type / High frequency type

This method estimates moisture from the electrical response by utilizing dielectric properties that change with moisture. While there are non-destructive and rapid measurement methods available, it is necessary to consider the influence of material, density, and shape.

infrared absorption type

This method utilizes the property of water absorption infrared light of specific wavelengths, and estimates moisture from the resulting optical changes. There are methods that allow measurement without contact with the object, and these are used for continuous measurements on manufacturing lines.

However, infrared measurements do not necessarily directly reflect moisture content. It is important to check the relationship with a reference moisture content and set appropriate measurement conditions for the object being measured.

For example, the same method may not necessarily be used for measuring a reference moisture content in detail and for measuring changes moisture content throughout the manufacturing process.

Determine moisture content using the standard method.

First, determine the standard moisture content of the object. moisture is done using a method appropriate to the purpose and object, such as a drying method.

Correspond measured values to reference values.

When measuring electrical or optical signals that change due to moisture, the relationship between the signal and a reference moisture value is checked.

The concept of calibration curve

One method involves representing the relationship between a measured signal and the actual moisture content using mathematical formulas or graphs, and then determining moisture content from newly measured signals. This relationship is sometimes called a "calibration curve."

What are we measuring?

The appropriate measurement method varies depending on the object being measured, such as food, paper, wood, powders, liquids, and films. First, confirm the type and condition of the object.

How much moisture are you measuring?

The appropriate measurement method varies depending on the range of moisture content in the object and the required resolution.

What level of accuracy is required?

The required precision and measurement methods differ depending on whether the value is for quality assessment or for understanding changes in process.

How quickly do you need the results?

The method you choose will differ depending on whether you have time to take measurements in a laboratory or if you want to quickly check the state of the manufacturing process.

Can we collect a sample?

If it is possible to collect and measure the target material, you can choose a method that assumes sample measurement. On the other hand, for materials that flow continuously, a method that allows measurement during process may be necessary.

Is continuous measurement necessary?

Intermittent measurements may suffice if you only need to check the finished product. On the other hand, if you want to understand moisture changes during process, online, continuous measurement is a viable option.

What will the measurement results be used for?

The required measurement method and operation will vary depending on whether you are recording moisture content, using it for quality assessment, or using it for process monitoring and condition adjustment.

Sample measurement and process measurement are not always used in isolation. Sometimes, a combination of confirming a baseline moisture content and monitoring changes during process is employed.

• What is moisture measurement in the manufacturing process? The concept of online and continuous measurement.