Controls-servicing company, American Control & Engineering Service Inc., Rose Hill, Kan., has faced another mystery - and solved it using crack detecting techniques. ACES periodically posts these seemingly mysterious episodes and their resolutions to its web site.

The Mystery. The customer, an aircraft company, purchased a large used oven and had it moved to the new location. The company set up the oven and lit it, but the unit would not stay lit. The customer removed ductwork and replaced the burner, but the oven still refused to stay lit.

The Clues. ACES sent its “CSI” (control systems investigator) to the scene. The oven powered up just fine for him. But wait! On closer investigation, he observed that the flame safeguard was lighting the pilot, then dropping out. He determined there was no flame signal because the flame rod was not sensing the flame.

A flame rod is a metal rod installed so that it intersects and is in contact with the flame when the burner is lit. The rod connects with a wire back to the flame relay, and an electrical current then passes through the rod. Because fire conducts electricity, the flame relay is able to sense whether or not the flame is lit. (ACES acknowledges that this is a simplified explanation and suggests exploring flame rectification for more information.)

The Perp. ACES’ detective traced the wire to the flame rod, which had a rubber boot over the end of it. Everything looked okay, but when he checked the rubber boot, it felt loose. He pulled it off and there was the culprit: the connector was broken.

The Solution. The ACES investigator installed a new connector on the end of the flame rod and re-lit the oven.

As a followup to this case, ACES says that many times, while investigating a control systems scene, its investigator will observe safety concerns distinct from the initial mystery. In this case, he saw several safety risks that concerned him.
  • The oven was a large direct-fired unit, which meant the burner’s combustion products entered the oven work chamber.
  • There was no makeup air for the burner, so anyone entering the oven would be subject to large amounts of carbon monoxide.
  • The exhaust was sent directly into the same room as the oven, putting workers at risk for potential carbon monoxide poisoning.
  • In addition, there was no purge timer for the oven, so if there was a gas leak and someone lit the oven, it could explode.
ACES alerted the customer to the safety problems and proposed corrective actions. The customer immediately took steps to implement the repairs.

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