Realtime Moisture Analysis


Thread Starter


I am in a situation where we are using forced air over steam coils to dry a product. The product travels on a movable conveyor in a closed
system with 7 different compartments. The heated air is forced through the product as a means of drying (from a moisute of ~35-40% down to a
moisture range of 10.5-11.5%). The only method of moisture measurement we currently use is an after the product has left the dryer and we have no moisture control. As long as the product stream is continuous, moisture control is tight. But due to product seperation issues, gaps
must be made and moisture control become erratic.

I am in search of some type of real time analyzer in the dryer itself that can provide either continuous moisture analysis of the product in of the various compartments or analysis of the air that I can correlate to a finished product moisture. The earlier that adjustments can be made, the tighter the control I can keep on the finished product. Any help will be greatly appreciated.

Marcos Thoni Bergamo

Dear 222

Your process is similar to a textile stenter (continuous dryer). The control strategy and instruments that we use may (or not) apply to your process.

It is possible to control the final moisture adjusting the compartments temperatures and the travel speed.

You can estimate moisture (in the products inside the drier) using contactless temperature measurement. Dried products will have higher temperatures.

Do you have more information (process diagram, actual process temperatures, travel length and speed) ? Is your product spreaded over the conveyor as an uniform surface? You can email it directly to me (the Automation List does not allow attached files).


Marcos Thoni Bergamo
[email protected]
Automation Coordinator
Santista Textil S.A.
I can't recommend an online analyzer, but it may be possible to develop an inferential model using an empirical modeling technique like neural nets. You would have to be able to take samples for offline analysis at the location where you want an analyzer and you may need to add some additional sensors. But if you can't find an acceptable analyzer, it might be worth the try.


Lou Heavner
Emerson Process Management

James Bouchard

Microwave non contact moisture monitors are used in a number of industries including pulp and paper and tobacco. The name of the company that make it does not come to mind at this time but it should not be hard to find.

James Bouchard
Johnson & Johnson Products Montreal

Dan Robinson

Moisture sensing devices are available from Viasala, a British company. These sensors may work, if oven temps are not too high.

Garry France

Hi, my name is Garry France and I am the Managing Director of an Australian Company called Callidan Instruments. At Callidan we produce a line of microwave moisture analysers to suit a wide range of applications.

Unlike surface measuring analysers (NIR), microwave technology uses a transmission technique such that the bulk of the material is analysed. Fluctuations in bed depth and product separation can be eliminated by measuring bed depth height or the mass of the product. Microwave antenna can be designed to withstand high temperatures such that measurement can be carried out within a dryer. Accuracies of 0.2% are acheivable.

Garry France.