low pressure gas valve

[killabyte]

hi, i need to find an electric or electronic gas valve for low pressure applications, i need to control by means of a computer, humidity, TEMPERATURE and other parameters

the gas comes from one of those gas cilynders.

regards

killabyte

 

[itsmoked]

Low pressure ... you mean less than 1000psi?

What gas?

What exact pressure range?

What exact electrical output?

 

[itsmoked]

Oh and what environment is the transducer going to be in?

 

[killabyte]

ill use one of those small propane gas cylinders, 100 or 60 lbs weight. not sure about pressure

electric output would fit transducer requirements, it will be in normal air.

it is to develop a huge greenhouse temperature (and others) controller.

on/off valve is not allowed cause i need to control the flow to the heater, so il need to deliver smoothly from 0% to 100%

best

killa

 

[MacGyverS2000]

I would think the easier solution would be to buy a pre-made heater and simply replace the rheostat already on the heater with a computer-controlled box. Why mess with the gas line itself when you don't have to?


Dan
Owner

http://www.Hi-TecDesigns.com

 

[killabyte]

the computer controlled box should consist of an electric transducer. now were developing an autonomous control system capable of deal with many other parameters.

the gas heater responds to money limitations in order to implement those systems in resource limited environments.

the gas valve is a must. im sure we dont know about it but somewhere it exists. if not we will have to develop such.

best

killa

 

[MikeHalloran]

I'd consider slow PWM modulation or PID control of a simple on/off gas valve, plus a pilot light or electronic igniter.



Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

Wow... You are playing with fire here. Seriously. This is not something you can just turn down and up. Fuel fed fire systems need multiple safety systems OR THEY WILL EXPLODE.

You need:
Test cycles.
Purge cycles.
Delays.
Ignition proving.
Ignition proving.
Flame out detection.

 

[itsmoked]

DOH!
Ignitor proving.
Ignition proving

 

[killabyte]

yes, pwm over a on off valve or solenoid? im not sure if it is allowed to be.

i think it would be somewhere a valve attached to a small motor to control that.

killa

 

[MikeHalloran]

No, I don't mean PWM to hold the valve partially open. I mean pwm like 10 sec on/ 50 sec off, like that. With igniter, safety valve, all that rot.

I don't think that you can throttle a gas burner over a wide range as you are assuming.

Once you've priced propane, you may go back to electricity.





Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

QUOTE: Once you've priced propane, you may go back to electricity.


I would add:
or blown all the glass out of the greenhouse and settled all claims and wrongful death suits...

 

[waross]

Hi killabyte
Try this site for controllers. They have models that can connect directly to the internet and be monitored and or controlled from computers. Many offer Time Proportional outputs, (Similar to pulse width modulation). I didn't see them today, on a quick check, but these people did offer a dual controller complete with a combined temperature/humidity probe. It was capable of independent control of both Temp. and RH., and the internet option was available.
I would suggest going between pilot light and full flame on a time proportional basis. The heating time constants in a green house don't require close modulating control.

http://www.omega.com/ppt/pptsc.asp?ref=DPi_Series&Nav=temm02

yours

 

[waross]

Hi killabyte
Here's another link. Temperature control, Humidity Control, Time proportional Output, PID Control, Internet conectivity, Probe Included.
These people also supply solenoid valves.

http://www.omega.com/ppt/pptsc.asp?ref=iTH&Nav=temp02

No, I don't work for them, but I have had good experiences with their products for years.
Please note the other posts as to not trying to modulate a small heater. If you're using a comercial heater, it will probably have a thermostat control. Replace the thermostat with the output of a time proportional controller. You may have good luck using a timer in series with the valve so that it ignores on times less than about 30 to 60 seconds.
MikeHalloran
If you substitute the term "Time Proportional Control" for PWM you will find this controller is described by your suggestion.
I believe that it can use a PID algorithm to calculate the Time Proportional Value.
yours