A shutdown mode has to be incorporated into the appliance in case the flame goes out. The intent is to control the flow of fuel. Let's take a quick look at the oil heat industry's primary control, focusing on the advancements made possible by microprocessor-based controls.
My candidate for a merit badge is commonly called a primary control. A primary control manages the operation of an oil burner, from blower operation, powering the igniter, to opening and closing the oil valve. These controls have evolved to meet the demands of our appliance designs, from a temperature-sensing control to today's electronic primary that senses flame presence to allow continued operation.
Managing an operation that includes a flammable fuel source requires the highest possible level of reliability. This is what many may take for granted.
Keep in mind, the safety of the structure and its occupants rely on this link in the system. Today's oil burners use flame presence through optics to determine operation. It's a reliable factor, allowing the control to react quickly to possible safety issues. Older thermal styles took longer to react because of the warm gases that passed over the helix as air passed through the burner, the boiler and the breech.
Another thing to keep in mind is that, while the burner is operating without a flame, the fuel unit is capable of delivering unburned fuel oil into the combustion chamber. Will this fuel be burned safely during the next complete combustion cycle?
A typical flame retention burner will produce a yellow flame. Yellow flame burners use a cad cell eye to sense flame, a highly reliable sensor that “sees” light by a resistance reading. A low resistance reading typically indicates the cad cell eye has a clear sighting of a bright flame.
If there is poor sighting or no flame, the resistance reading increases. Here is where the primary takes over as our sentry, managing burner operation during the combustion cycles. If the eye senses flame failure, creating an unsafe condition, the primary will “step in” and shut down the burner.
Why Change?OK, that is the flame safety aspect, but where did the control evolve from and why should you be impressed with today's microprocessor controls? After all, the cad cell relay has been around for nearly 50 years. Why change?
Today's oil heat equipment is hardly the same as the coal-converted “snowmen” found in so many basements of the past. Manufacturers of burners and appliances have tightened up engineering standards to burn fuel as efficiently as an application allows. Along the way, the housing industry changed construction standards.
All of this, coupled with a heightened level of energy conservation, has affected appliance design. Today's heating appliance has to perform with close tolerances, each time with no room for exception.
The primary control from the 1960s just doesn't do the job today's equipment dictates. Solid state components and electromechanical relays limited older designs. The options available centered on safety timing, air-conditioning subbases and an occasional flame delay/blower on devices.
The circuitry limited the number of options, as well as the need to stay “price competitive.” After all, the appliances dictated simple controls. Why add features that might drive the price too high?a
Microprocessor-based primary controls came about in the late 1980s and early 1990s. R.W. Beckett and CCT/Carlin introduced some of the first versions, with others introducing their version shortly after.
The first Beckett version offered “on board” diagnostics through LED displays. This small step was readily accepted and quickly found its way into CCT/Carlin and other lines.
Techs were hesitant at first, but have started to grasp the idea of looking to the control for quick diagnostics. That first version from Beckett introduced our industry to full, solid- state controls, foreign at first, but soon to gain acceptance. Another plus with the early Beckett control was that it was unaffected by vibration, a situation that had crept into one line of controls, causing phantom “have to reset” service complaints. The industry was one step closer to accepting microprocessor-based controls.
CCT/Carlin was an innovator, offering a line of full-featured controls. One favorite selling point of their control is their “Serviceman's Reset Protection” feature. This feature prevents a “flooded chamber” from repeated pushing of the reset button.
Anyone with more than a couple seasons in the oil service industry has a story about a flooded chamber, caused by a well-meaning homeowner who kept pushing the reset. I've never understood why you'd keep trying to start the burner if it just won't run. It's like trying to start a car until the battery finally dies. They push that little button until their finger goes numb, and then call for service. What they don't realize is each push sends unburned fuel into the chamber.
When the burner finally lights there is too much energy for the appliance. CCT/Carlin came out with a “three strikes” control, where the homeowner could try the button three successive times, and then the control locked up, preventing any more “button pushing,” as well as additional fuel for the fire.
Other AdditionsAnother added feature is delay timings. Now an oil valve can be used to delay the start of flame, allowing the burner's fan to establish draft direction before ignition. This feature was available in the past; however, microprocessor-based controls established precise, consistent timings.
In the past, timings could change because of ambient temperatures. The next feature made available through microprocessors is an “end of cycle” carryover of the burner fan, with no flame. This “blower off delay” removes any residual combustion gases, reducing odor complaints.
Precise timing sequences are one of the key benefits of microprocessor controls. The precision of the timing sequences allowed Beckett, CCT/Carlin and others to introduce recycling primary controls.
Recycling controls attempt to prevent nuisance loss of the burner caused by intermittent problems, such as sudden draft changes or small amounts of entrapped air in the fuel. The control will return to a beginning cycle and attempt to restore operation when a loss of flame occurs.
Reliable operation of a solid-state control is dependent on the quality of the wiring. There must be proper, complete circuits from the panel to the control and back again. Grounding also is critical. Don't rely on the boiler piping to ground an appliance, use the ground and bond the wire.
Microprocessors will do some strange things when there is an “open neutral” caused simply by a loose wire. If your customer complains about the VCRs that fail or the microwave that doesn't work, it might be a good time to recommend an electrician.
The next step is already here. CCT/Carlin and its competitors have control packages available to fully monitor the burner operation. You may find that the cad cell eye is replaced by a UV detector for additional functionality.
These controls are built on the microprocessor within the electronic primary. They monitor flame quality, cycles of operation and can “call out” information to a central monitoring station. When the control “calls out,” it may be just a routine check-in to deliver information or it may call out requesting service.
The control can determine if the flame has degraded, requiring service soon or even call out for a service call because of not enough or no heat. How's that for advancements? It can even monitor oil use, accurate to levels that degree-day-based systems only dream about.
Let's recap the benefits of the oil industry's new electronic primary controls:
- Precise timings for consistent burner performance.
- Enhanced safety ability, adding another step of protection.
- Available blower on and blower delay off cycles so the equipment can match installation requirements.
- Interrupted ignition to reduce energy costs and parts replacement.
- Operation monitoring, the next step in controls to make your customers' equipment fully functional, right down to calling for an oil delivery or a periodic service!
Some of the terms you will encounter with new controls are:
Recycle: To attempt to light after the cad cell senses flame failure
Preventilation/blower on delay: A blower on cycle before the start of the flame. The purpose is to establish draft and purge the combustion area of any unburned vapors.
Blower off delay: A cycle where the blower carries over at the end of a call for burner. Purpose is to rid the chamber and appliance of any residual combustion gases.
Safe start: A preliminary start of the burner cycle where the control observes the chamber for the presence of light/flame. If the cad cell senses light it will hold the control from starting the burner.
Lock up/latch up: The control is disabled from being reset by the customer after trying to reset the burner three times. The control must be “unlocked” by holding the reset in for a specific period.
Intermittent ignition: The control powers the transformer or igniter for the full length of the burner cycle.
Interrupted ignition: The control will drop out the transformer or igniter power after a specific period of time. This feature saves energy and replacement of parts.
Ready for the next step in heating? The oil heat manufacturers have made their products easier to work with, highly reliable and safer.