Proportional controllable device?

[sliceman]

Hey all,
I am brand new to this type of design, so this may be a simple question:
I am looking to add temperature and humidity control to an enclosure. The controls will be provided by another dept, I just need to spec the heating and humidification components. However all of these components have to be proportionally controlled - is there a way to know (other than calling the company) whether a heater or humidifier will work through proportional control? For instance, these heaters from Omega fit the power requirements I need, but I can't tell if they can be proportionally controlled:
option 1:

http://www.stego.de/fileadmin/Bilder/PDF/English_US/HG140us.pdf

option 2:

http://www.omega.com/pptst/SREH.html

Can anyone with experience give me a clue, here?

 

[itsmoked]

Unless a heating device has something mechanical involved you can usually turn them on and off as often as you desire.

Your two choices can, specifically, be turned on/off as fast as you desire with NO issue at all.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[sliceman]

Can you tell if they could be run on lower voltages to produce lower amounts of heat, and controlled that way?

 

[itsmoked]

Certainly!

Both the units you've selected will self limit to some temperature. This means you can only turn down the heat using any of your methods from some maximum value these units top out at.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[roydm]

The usual way to proportional control a heater is to pulse it On and Off (time duration)
For example you set up the controller to have a 10 second cycle time.
For 10% On 1 second Off for 9
For 50% On 5 second Off for 5
So you pick a heater that has more than enough capacity
The first example has built in temperature control, I think that would be hard to control, the second type is easier.
You need to tell the controls people that's what you intend to do otherwise they may supply a controller with 4-20 mA output, you need one with a solid state time duration output.
Roy

 

[sliceman]

Thanks, guys - I really appreciate the help and responses.

 

[LionelHutz]

I'm sure I have seen solid state relays that take an analog input signal (4-20mA or 0-10V) and convert that into a duty cycle. They also use zero crossing detection to supply full cycles of power to the heaters.

You can also use phase controlled SSR's but they can put more harmonics and noise on the power.