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FAQ: Burner Control Units – Flame Signal Strength

Q: I’ve got a PF-19 flame safety system incorporating PFU 760 burner control cards, and I keep faulting-out. It seems to be due to loss of flame signal, but I can visually verify flame. How do I check the flame signal on my PFUs? What could be causing this problem?

A: Elster Kromschröder burner controls read flame signal either via Ionization Electrode (also called Flame Rod or Sensing Electrode) or UV Sensor. It is worth noting that Elster Kromschröder burner controls should be able to accept a flame signal from nearly any manufacturer’s Ionization Electrode, but if you’re sensing UV, then an Elster Kromschröder UV Sensor must be used.

Combustion 911 offers the full range of Kromschröder burner controls available for the North American Market, and can also provide European Standard units, upon request. These include the BCU (370, 460, 465, & 480), IFD 258, and PFU (760 & 780). Each have their merits, but we’ll discuss them only briefly as they pertain to the current topic.

The most concise information available for any Kromschröder product can be found in the manufacturer’s literature. Combustion 911 works to maintain the literature available on our product pages, to ensure that the latest revisions from the manufacturer are the ones you see. That being said, the sequence for reading flame signal strength on a PFU 760 is found in the Technical Information for that product, under the section called “Scanning the parameters.”

The procedure for reading a flame signal on either a PFU 760 or 780 is very similar. These models boast a two-character display from which can be read information regarding the various parameters. To toggle from the current view, press and hold the Reset/Information button for approximately two seconds. As this button is held, each parameter’s number is shown in sequence. So, if you would like to view parameter 01, continue holding this button until “01” is displayed, and then release. For PFU 760, the flame signal of the burner is displayed in parameter 01, with a measuring range of 0-30 micro-amps. Since the PFU 780 can monitor a pilot burner and a main burner, the operation for this model is only different in that parameter 01 will return the flame signal for the pilot burner, while parameter 02 will return the flame signal for the main burner, each with a measuring range of 0-30 micro-amps.

The other burner controls mentioned above, BCU (370, 460, 465, & 480) and IFD 258, operate similarly to the PFU when it comes to scanning parameters and reading flame signal strength. During operation, the two-character display on any of these models can be used to show the various parameters. Press and hold the Reset/Information button for approximately one or two seconds to toggle through the parameters. For each of these models, parameter 01 displays the flame signal in micro-amps. The exact range will vary between models, so please check the literature for details. For the BCU 480, like the PFU 780, parameter 01 reads the flame signal for the pilot burner, while parameter 02 reads the flame signal for the main burner.

Reading the flame signal from a Kromschröder burner control is easy. Troubleshooting the cause of a drop in flame strength might be a little less so. We’ve listed some common causes, with brief description, below.

1)    Corrosion of the electrode: If flame signal is being read via Ionization Electrode (also called Flame Rod or Sensing Electrode), and the signal strength seems lower than it ought to be, then this is a good place to start. Electrodes are consumable items, and so will deteriorate over time and need to be replaced. Additionally, if the furnace has been idle for a week or more, it is common to see rust on the exposed metal parts. Cleaning these should restore operation, but please keep in mind that they may have to be cleaned following each idle period.

2)    Corrosion of the spark plug at the base of the electrode: The Ionization Electrode should terminate in a Spark Plug, which is where the Ignition Cable connection is achieved. Spark Plugs are consumable items, and so will deteriorate over time and need to be replaced. However, if the furnace has been idle for a week or more, it is common to see rust on the exposed metal parts. Cleaning these should restore operation, but please keep in mind that they may have to be cleaned following each idle period.

3)    Accumulation of dirt on the electrode or on the burner grounding surfaces: Before attempting involved, expensive corrective measures, try cleaning your equipment. Dirt, soot, carbon, and metal dust can accumulate on electrodes and grounding surfaces, interfering with electrical operation.

4)    Residue or buildup on UV lens: If your system monitors flame using UV sensors, check the lenses. In the event that your flame signal reading seems lower than it ought to be, you may find that these lenses are clouded with soot or other material. If this is the case, then instituting a periodic cleaning schedule may be a smart preventative measure.

5)    Change in air/fuel ratio: Changes to the air/fuel ratio at a burner can occur intentionally, accidentally, or as a result of operating over time. Burners should be tuned periodically in order to ensure that the desired ratio is maintained, and a weak flame signal could indicate that a burner needs to be tuned. However, please note that some burners’ flame signal strength increases when the air/gas ratio changes. This is usually seen on burners that are set to high excess air or excess fuel.

If you continue to experience problems despite your best efforts, you may want to consider a service call from one of the talented technical specialists at our sister company, Olstrad Engineering. As always, thank you for visiting Combustion 911.

Posted by  b-olstrad ; Published March 15, 2013

 Categories: Burner Controls, Electrodes, FAQs, Industrial Burners

 Tags: , , , , ,

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