# Flame detectors

A

#### Alberto Lucas

For a fired-heater that has 48 burners/pilots, and that will burn only fuel gas, what is the flame detector technology recommended (UV, IR or Flame Rods)? Flame detectors are a consolidated and reliable way of monitoring a flame? Best, Alberto Lucas

S

#### SPECTRUM ENGINEERS

uv is recommended for this kind of application.

J

#### Jeffrey W. Eggenberger

I have found the UV systems to be easier to maintain. The flame rods have to project into the flame, and therefore have a limited life. Jeffrey W. Eggenberger Electrician: Industrial, Commercial, and Residential

B

#### Bruce Axtell

First, consider your application. Will it run continuously, that is, more than 24 hours at a time? Will the process ever change, from short-term to long-term? (e.g., it may be an 8-hour batch process now, but what if more shifts are added and they run continuously?) Flame rods are inherently, fail-safe. An ac voltage is applied to the rod, and the flame completes the circuit. The rod behaves like a diode, and rectifies the ac. The dc current is then detected and used to prove flame. UV sensors, on the other hand, are a gas-filled device, and can fail in an ionized state. Failure mode looks as if flame is present, even if there is none. Normally, most modern flame relays check for an ionized state when starting an ignition sequence. They will not allow the sequence if it "sees" flame before ignition. However, if the flame unit is okay to start, but subsequently fails during the process, the flame relay cannot detect this and will allow raw gas to continue dumping into a burner which may be out. Thus, UV is recommended for only short-term applications. UV units should be changed every 2000 hours. However, if your process runs 24/7, and you must use UV due to burner configuration or other reasons, then select what is referred to as a self-checking UV system. The UV flame detector has a built-in shutter, which opens and closes. The flame relay checks for an "off" condition of the UV detector during the closed shutter period. If it detects the UV unit is on when the shutter is closed, it then shuts down the burners. And the choices are listed in order of $, $$,$$$. Bruce Axtell Engineered Control Systems 763-421-8787 763-712-5477 fax [email protected]

A

What are some sources of flame detectors for intermittent flame presence? I found some flame sensors and they are mega too big for my application. IF they were, say the size of a pencil or shorter, would be acceptable.

E

#### Ed Mulligan

Go to "http://arsrobotica.com/":http://arsrobotica.com/ and search on "UV". There are links to a few different UV detectors listed. These are small units suitable for mobile robot use.

Ed
Speaking for me, not for Starbucks. . .