Flame detection

ddeshi2 · Jun 6, 2011

Hi all,can anyone please tell me what are the different methods used to detect flame in a burner. I know they use flame rod, UV and IR scanners to detect the flame ..but are there any other methods to detect the flame?? And also what are the best flame rods, UV and IR scanners out there in the market? Any help would greatly appreciated.

Thanks,

Ding.

Dravik · Jun 6, 2011

Interns!

TConnolly · Jun 6, 2011

Flame rectifier. This is by far the most common method.

A flame can conduct electricity. A plate and a thin wire are placed in the flame. The thin wire is the rectifier cathode and electrical current can easily flow from it through the flame to the large surface area of the plate anode. However because of the proportionally much smaller surface area of the cathode (wire) current does not flow as well in the reverse direction.

No current = no flame.
AC current = someone has tried to bypass the flame detector
DC current = flame is present.

http://customer.honeywell.com/honeywell/ProductInfo.aspx/Q179B1042

icky812 · Jun 6, 2011

I wouldn't say that a flame rectifier is the most common method.

Nearly every water heater made has used Thermocouples to sense flame and keep the pilot lit.

harryting · Jun 6, 2011

Depend on the purpose, I suppose. I see mostly UV detector. It probably is the most reliable since they are used for safety interlock/shutdown.

Just google "purple peeper"

TConnolly · Jun 6, 2011

That would be true for standing pilot type water heaters. And there are a lot of those out there. There are even a lot of standing pilot furnaces still out there. So T/C is probably the most common. But pretty much all modern electric ignition residential furnaces and the newer electric ignition water heaters use flame rectifiers.

ceilingwalker · Jun 6, 2011

All of our gas fire furnaces use Protectifier Control's which use UV sensor's as Harryting mentioned, for ease of use in interlock/safety control circuit's.

ddeshi2 · Jun 6, 2011

Thanks yall for the help. But I'm looking for a high temperature flame detector (it should withstand a temp. of around 2500 F). Can a flame rectifier or Purple peeper withstand the above mentioned temperature?

Fropitar · Jun 6, 2011

ddeshi2 said:
Thanks yall for the help. But I'm looking for a high temperature flame detector (it should withstand a temp. of around 2500 F). Can a flame rectifier or Purple peeper withstand the above mentioned temperature?

Typically a UV Scanner is put on the end of a burner, and mounted up via a short nipple and an insulated coupling so it doesn't get too hot. It "See's" the flame, it doesn't need to be -in- the flame, or furnace. Very common.

ddeshi2 · Jun 6, 2011

Ok I read this in a forum...

"In the US, code (NFPA, I believe) states that burners that run continuously for 24 hours or longer use UV detectors that 'self check', which involves a mechanical shutter mechanism that blocks the flame path temporarily so that an internal check can be made to determine whether the UV sensor has 'burned in' in the "ON" state. Any sensor doing so can not detect a flame failure, which is what the shutter mechanism is simulating.

Obviously self-check sensor mechanism are multiples the cost of ordinary UV sensors."

So does flame rectifiers, purple peepers and UV scanners have self check mechanism? I found that purple peepers have self check mechanism.. but what about other devices??

jrwb4gbm · Jun 6, 2011

As I remember, some of the older UV sensors were connected to a module on a controller chassis. This controller chassis had two relays to guard against contacts "sticking" or welding and they also checked to see that the UV sensor changed to the proper state between flame present or absent. One thing I remember is that any and all flame systems went thru extensive UL testing and had to be approved by them (UL) before they could be sold to the public. Anything less opens the door for extreme liability including voiding liability insurance coverage. I'm pretty sure that the Protectifier, Honeywell and Fireye systems are still using an approved module and controller chassis system, or something similar to this.

danw · Jun 6, 2011

ddeshi2 said:
So does flame rectifiers, purple peepers and UV scanners have self check mechanism? I found that purple peepers have self check mechanism.. but what about other devices??

The purple peeper is a nickname for Honeywell's self-check scanner:

Honeywell also has a UV detector that is not self-checking, the Mini-Peeper:

The relative sizes are not exact, but there is a considerable difference in size.

Each requires a different flame detector module on the flame saftey controller.

Rectifying flame rods do not have the same failure mode as UV (under continuous exposure) so there is no self-checking flame rod.

Infrared detectors have lower temperature exposure ratings than UV; not for you application.

ddeshi2 · Jun 7, 2011

Thanks yall for the help. Now my question is we are using a class 3 igniter .. so does it have to have a self-check mechanism ? And is it true that any burner that burns for more than 24 hrs continuously should have a self-check mechanism? As ours is a very small burner that burns a flame around 2500 F.

TWS · Jun 7, 2011

From the NFPA 85 2011 code.

Section 5.3.4.1.1.3 Class 3 igniter. Section C states the Main flame shall be proven by a flame SCANNER.

I suggest you by yourself a copy of the code or consult with a subject matter expert in burner controls.

Clay B. · Jun 7, 2011

Local Rules Apply

Your local rules are going to apply here but in most cases class 3 and 24 hour burn means a self checking system is required.

Your local supply house should have a copy of the rules that apply specifically to your area. My guess key word guess... You are going to need a UV with self checking.

Personally I would buy this as a complete kit Flame controller with sensor so you do not end up with alot of headaches later.

Flame detection

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