How aggregate moisture measurement methods compare
Four methods are in common use on batch plants: oven drying, TDR, microwave and near-infrared. They differ less in headline accuracy than in what volume of material they actually see, and how they behave as the sensor wears.
TDR vs microwave
Both claim comparable accuracy. The difference is measuring volume, wear behaviour and whether the sensor reads through a cover.
TDR vs near-infrared
NIR is fast and non-contact but reads the surface. On a stockpile or a belt, surface and bulk moisture are not the same number.
Moisture meter vs oven drying
ASTM C566 is the reference method and stays the reference method. It is also hours behind the batch it was meant to control.
What each method actually sees
| Method | Measures | Result in | Note |
|---|---|---|---|
| Oven drying (ASTM C566) | whole sample | hours | Reference method. Destructive, and too slow to correct a batch. |
| TDR | material volume | seconds | Guided radar pulse timed to one picosecond, read in disks along the sensor. |
| Microwave | penetration depth | seconds | Depth depends on the sensor and the mounting. |
| Near-infrared | surface layer | instant | Non-contact. Fast, but surface moisture is not bulk moisture. |
Comparisons on this site are drawn from manufacturers' published specifications. Where a figure is a manufacturer's own claim, it is described as such.
Which method fits your plant?
It usually comes down to material conductivity, particle size and where you can physically mount a sensor. Send us those three and we will tell you straight.
Houston, Texas · Most quotes answered within one business day