Grainstoves from J. A. Mitchell Marketing

Chapter Eight: The Fuzzy Logic Processor

The processor in the PC-45 is more advanced than the processors in the other grain stoves on the market. Harman uses a fuzzy-logic processor to monitor and control combustion. The fuzzy-logic processor will constantly adjust to keep the temperature at the desired level. It will slow the feed rate down as the temperature nears the desired temperature and then will feed just enough fuel to maintain that temperature. Many of our competitors, on the other hand, use a basic on/off processor. The stove burns full-out until the desired temperature is reached and then shuts-off. When the temperature falls far enough, the stove begins feeding again. There are two problems with such a basic processor. First, process can never maintain the desired temperature; the temperature goes up and down as the stove constantly kicks on and off. Second, because the stove is kicking on and off and not burning constantly at a steady rate, efficiency is lost as the process is constantly stopping and starting.

PC-45 Logic Board

Our fuzzy-logic processor does not use a simply on/off system. The processor is constantly adjusting the amount of grain the auger is feeding the fire. It adjusts the amount of grain by increasing or decreasing the length of time the auger feeds the fire during its 15 second cycles. The auger feed time is adjusted by a 1/10 of a second per 15 second cycle. As described above, the processor will start to lower the amount of grain being fed into the burn pot as the temperature approaches the desired level. It reduces the amount of grain it is feeding until it reaches an equilibrium and is feeding the proper amount every 15 seconds. This system is much more efficient and stable than the on/off cycle used by many of competitors.

In addition, the fuzzy-logic processor will override manual controls set by the owner if these manual settings are problematic or incompatible. For example, if the owner sets the room temperature setting to a very high 80º and then manually turns the combustion fan to low, the processor will override the low fan setting because this setting is incompatible with the desired temperature setting.

You also have the option to set the stove to “Stove Temperature.” This setting is preferable if the stove is in a small room. When the stove is in a small room it heats the room up quickly and then the room sensor reaches desired temperature quickly and the processor begins slowing the burning process down. However, when the stove is placed in a small room, it is generally used to heat more than just that room, so the “Stove Temperature” setting allows you to set the stove so it puts out heat at a constant rate, regardless of the temperature in the room that the stove is in. Again the fuzzy-logic processor adjusts the feed rate and other factors so that the stove constantly puts out the right heat.


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Warning, J.A. Mitchell Marketing Ltd. is not the manufacturer of the Harman PC-45 or any other product. J.A. Mitchell Marketing Ltd. is not responsible for any loss or damage caused by the Harman PC-45 or any other product. J.A. Mitchell Marketing Ltd. provides no representations or warranties. If you are confused or unsure at any point, contact your local Harman dealer.