PLC based Gas fired Oven Control Interface devices ie honeywell

rkduet

Member
Join Date
Oct 2003
Posts
23
Is it neccessary to incorporate burner control devices such as Honeywell's Burner Control 7800 series with a PLC? Or is it more feasable to utilize direct input to a PLC for flame detection and direct output for igniiton control? Also what are the benifits of having seperate temperature displays as the Honeywell UDC2300 Mini Pro for overtemps. Could these not be seperate inputs to the PLC? Or does the current standard prohibit complete PLC control and require these external devices?

Looking for answers again.
Best Regards

rkduet
 
rkduet,

I have controlled gas burners both ways: Completely PLC, or alternatively using a Honeywell Burner Relay combined with a PLC. The improtant point is that if you develop your own burner control system using only the PLC, then it has to be inspected, certified, verified, and approved by the state authority having jurisdiction over burners. Otherwise you will be violating several codes.

It is usually easier to just buy a burner relay that already has the proper certifications, then use a PLC for the inputs and outputs to the burner control relay. When you do this, there are some outputs that the PLC is not allowed to control directly (such as the combustion air blower, the gas shutoff valves, and the pilot valve. Basically you use the PLC to issue a Start/Stop command to the burner relay, then you monitor the various inputs and outputs of the burner relay.
 
I always control my burners with a burner control relay (not always honeyweel).
It's easyer, the costumer gets normalised equipement and I avoid the legal problems.
For the PLC, the burner is just one output with one alarm.

Also for maintenece, having burners control relays is easyer.


João
 
I have done some large (10 MW) burners using PLC Logic only. It demands a fairly rigorous and structured programming technique, but the big advantage is it is possible to create complete alarming and diagnostics for the operators and service people.

The system I wrote gave not only a description of what failed, but exactly at what step the failure occurred. Every possible failure at every step is monitored. If the system fails to ignite, the exact reason and state of the system is displayed.

This has made troubleshooting the boilers exceedingly easy. They virtually tell the service guys what to fix, and greatly reduces the MTTR. It certainly gave a more comprehensive and complete system than the older relay controlled boilers next door.

But whether it is worth doing is going to depend on how easily your national regulatory body accepts this approach, and on whether your end-users can gain a benefit from the more sophisticated PLC system.
 
When we design thermal oxidizers, we typically use a Honeywell flame relay with a UV detector just to give us a "flame on" input into the PLC. We control the gas valves, blowers, and ignition from the PLC. This gives us a little more startup and shutdown flexibility.
 
To be used in safety applications, devices need to have redundant circuitry and such. You should never, never use a PLC for burner control without some sort of hardwired safety device.
 

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