AVR-Chat

Maybe add a pressure switch, or even a simple sail switch, on the input 
to ensure there is adequate gas supply and limit switches to indicate 
full open and full closed for the valve.

The reason for the supply switch is we had a customer once who 
discovered the hard way that inadequate gas supply will create 
incomplete combustion, excess production of CO rather than CO2, and 
caused other problems in their customers' operations.  You may also want 
to alarm if there is a supply loss.


REB


Bernd Felsche wrote:

>On Saturday 21 May 2005 14:39, John Samperi wrote:
>
>  
>
>>From what I understand so far the valve controls gas to a burner
>>which needs to keep a temperature of about 450 degrees celsius
>>(flaming hot!!) perhaps +- 30 degrees. A Mega16 (possibly) will
>>be monitoring the thermocouples and will adjust the opening of the
>>valve to maintain the temperature. So, yes I have some feedback
>>on what's happening with the valve perhaps 1 or several seconds later.
>>    
>>
>
>You should still be controlling the output, not the input. :-)
>
>You need to understand the process a bit better, I think. The delays
>in the system will otherwise create instability. Such instability
>may be invisible during normal operations but typically has
>actuators moving unnecessarily as they hunt around the set-point.
>Nobody wants that because it wears everything out very rapidly.
>
>Look at the thermal constants, etc. Maybe you can measure the
>desired temperature (not the flame) directly using a pyrometer (they
>can measure changes quickly < 0.10 seconds).
>
>You can also, by knowing the thermal constants, do "predictive"
>control based on the previously-measured response of the system and
>the present state of flow; especially if the thermal response is
>slow.
>
>If you're doing something like (hypothetically of course)
>controlling the temperature of a hot-dip galvanizing bath, then the
>main perturbation to the system is the immersion of cold steel which
>will result in an observed "plummet" in the bath temperature;
>especially if the bath contains "minimal" zinc. The rate at which
>the temperature initially falls is an indicator of the thermal
>capacity of the object being inserted and therefore the amount of
>energy that the increase in energy to be provided by the gas flame
>increase so that the minimum tolerable temperature is maintained.
>
>It is of course impossible to maintain an exact temperature. Any
>control system requires an error signal to attempt to maintain the
>required output.
>
>  
>
>>The valve will be moving a maximum of 1/2 turn, so no high speed
>>sensors are needed. An Absolute Position sensor would be nice
>>to have to find if the valve has moved or if the valve motor
>>has moved in the right direction or not moved at all i.e. faulty
>>motor, broken wire, jammed/locked valve etc. as a safety precaution.
>>    
>>
>
>Monitoring motor current draw may be sufficient to detect a jammed
>valve. Relative positioning is OK as long as you can map flame
>temperature against step size (I'm assuming a well-regulated gas
>pressure and sufficient oxygen). The "current flame" could probably
>be used as a reference point against which to apply the delta.
>
>  
>