Micro Moisture Meter
Types of micro moisture meters
Generally, the micro moisture meters are categorized into two types by measurement method : electric property and light. The meter which utilizes electric property measures electric resistance values or electric capacitance values, and replaces them with moisture values. The meter which utilizes light measures the degree of absorption of light.
Comparison on the features of moisture meters
| Type of moisture meter | Advantages | Disadvantages |
| Electric resistance | ▪Less affected by specific gravity. ▪Setting of specific gravity and thickness is unnecessary. |
▪Needle insertion is necessary, which damages measured object. ▪Affected by surface condition in case of needleless measurement. |
| Electric capacitance | ▪Max. several centimeters from surface to inside can be measured. ▪Easy to downsize like a portable type. ▪Less damages for measured object. |
▪Setting of specific gravity and thickness is necessary. ▪As the measurement focuses on the surface, the internal deep part cannot be measured accurately. |
| Microwave | ▪Internal moisture including the deep part can be measured. ▪All quantity can be measured in line. ▪Fastest measurement speed. |
▪Setting of specific gravity and thickness is necessary. ▪Machine is large-sized. (in-line type) |
| Near-infrared light | ▪Measures surface only. ▪Easy installation. ▪Effective for thin materials. ▪No damage for measured object. |
Measures several hundred micrometers (1mm or less) of surface only. ▪Sometimes affected by color. |
| Neutron | Measurement including internal moisture is possible. | ▪Lifetime of generator is not so long. (Generation reduces by half in 3 years or less, which requires replacement every few years.) ▪Vulnerable to impact due to a very thin film to consists of a receiver. ▪Slow measurement speed. ▪Neutron is more difficult than β ray on shielding, so it is harder to prevent exposure than β ray. ▪Dangerous without knowledge due to the characteristics as radiation. |
| Dry weight method | Relatively accurate as the weight is measured after drying. | ▪Measurement requires a lot of time, so in-line measurement is impossible. ▪Needs to cut out a sample. ▪Strictly speaking, in case volatile elements except water vapor, the correction of such elements is needed. |
| Chemical measurement method (Karl Fischer) | Accurate measurement of water only is possible. | ▪Measurement requires a lot of time, so in-line measurement is impossible.
▪Needs to cut out a sample. ▪Reagent is expensive. ▪Difficult to measure large volume. |
Difference between “Time-measurement” type and “Attenuation” type
| Type of moisture meter | Time Measurement Type (new) | Attenuation Type (conventional) |
| Measurement method | Measures the time of microwaves. | Measures absorption (attenuation) values of microwaves. |
| Accuracy | Much more accurate compared with Attenuation type. | Almost same accuracy as Near-infrared-type moisture meter. |
| Size | ▪Larger sensors and control panel compared with Attenuation type. ▪5 kinds of sensors by size. |
▪Control panel and sensors are potable enough to carry by yourself only. ▪2 kinds of sensors by size. |
| Price | More expensive compared with Attenuation type. | Same price as other types. |
| Measurement range | Thickness : 0.1mm to 500mm | Thickness : 3mm to 150mm |
| Measurement range of moisture (%) | 1% (thickness : 0.2mm) to 60% (thickness : 500mm) | 2% (thickness : 3mm) to 30% (thickness : 150mm) |
