Temperature and Humidity control

You don't mention what temperature and humidity ranges or set points you would like to control, but I'm going to assume that whatever the levels you wish to achieve can be obtained. You also didn't mention what the volume or mass of your system is, not to mention the precision to which you would like to control it.

Separate PID (whether using PLC's to achieve PID or not) controllers are one way to solve the problem: One to control temperature, and another to control humidity. Psychrometric charts will tell you how many pounds of water air at a certain temperature will contain at a given R. H., which adds to the mass of your system and will affect the system characteristics.

More details would help.

Thanks for your answer Bill, going in detail.

- Temperature range: 25-300ºC

- Humidity:0-100%HR

- Volumen mass: air around 0.3 cubic meter

I wonder if you may know any articule or web related cotaining studies or tests talking about this situation

Thanks again

Well, I can tell you real quick that you will have to pressurize your vessel if you want any humidity at 300^oC!

I don't know of a study, but I have done this sort of thing before.

What are you planning to use as a R. H. sensor? Most won't take the temperature, and some won't take the pressure you would need to go to 300 C.

I know bill,anyway i hope to reach following extreme conditions:

- Extreme 1: 10%HR @ 300ºC

- Extreme 2: 100%HR @ 130ºC

For first condition there is no need of pressurize vessel but i need it for second one, anyway just a few kPa.

For humidty mesurement I tried to find direct-sensor measurement but they are very expensive, for measuring HR at 130º the price is around 1000 $,so i decided to go ahead measuring Wet temperature using Pt1000 sensor and spraying water on it.

My psychrometric "calculator" yields:

Condition 1: 300^oC @ 10% RH: Pressure = 92.4 Bar = 9240 kPa saturation pressure @ dry bulb temp.

Condition 2: 130^oC @ 100% RH: Pressure = 2.7 Bar = 2711 kPa saturation pressure @ dry bulb temp

Temperature measurement is not so difficult or expensive, and there's no need to spray water on a Pt1000 sensor.

I'm not sure where you're going with this . . .

What's the process?

cooking application,

Pt1000 with water spraying is the cheapest way to measure temperature, I can tell that for 140ºC vapour I coould only find humidity sensor for 1000$

Please allow me to add a little something, for your application I would suggest DDC (Direct Digital Control) to control temperature and humidity. When you add PID (Proportional Integral Derivative) you can get a stable and controlled result, but at temperatures that high you will need to get industrial grade sensors and humidifiers. For this application I would suggest 4 to 20 ma devices because of their accuracy. as far as studies check the ashrae web site.