Suggestion:
Contact some of the following manufacturers and ask for an application engineer:
1.
NDC Infrared Engineering
626-960-3300
2.
Davis Instruments, LLC
800-548-9409
3.
Soilmoisture Equipment Corp.
888-964-0040
4.
Dryning Technology
409-385-6422
5.
AgriChem, Inc.
612-434-6755
6.
Scale-Tron, Inc.
800-632-7083
The application will determine the selection of sensor and the selected sensor its accessories including the circuitry.

Thanks Bartos for the info.

Mark

For the sensor head try browsing on Microsyst MS8005 RH sensor and also available w/ circuit from National Semiconductor Application sheet. Good luck!

Try Betatherm Sensors Ltd. at WWW.betatherm.com

What is the range of humidity or dew point are you looking for? This makes a difference in the sensor technology.

I designed a circuit that runs off 24vdc, operates a solenoid, and senses soil moisture content. Wanta talk? Uses a Nat Semi chip...

Firstly you need to know the application, and any special conditions, whether you require a submersible, contact type, a Infra-red or Microwave (non-contact) type, etc...etc..

It often helps, if you describe all the details firstly and then ask questions.

my interest in this was that I too am looking for a Non-contact Moisture sensor, But I have another cheaper idea, and would want to know views of some Electronic champs around here, as I am into automation, (but not an electronic Engineer), What I want is to meaure the moisture of Product, (Contact type) by measuring the Conductivity/Resistance, draw a table, and convert them in the PLC and give out the result, PLC is no problem for me, ButI am looking for someone who could guide/assist me how to construct this SUPER DOOPER capacity Sensor (You can take an example of the Multi meter set to Conductivity/Resistance, with super sensitivity.)
Would apprecite any help at iel@cyber.net.pk