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Three Zone Temperature Controls
The standard configuration of all Paragon kilns uses a single thermocouple (1 Zone, also known as Single Zone) located near the middle of the kiln wall behind the control box. The Sentry 2.0 Digital Controller constantly computes the temperature of the kiln through the single thermocouple and then adjusts the firing speed and temperature based upon a moving average of those temperature readings. For most customers, the single zone monitoring system works extremely well. But, as kiln sizes increases, the single zone control is not always adequate. There are instances when a kiln user, especially somebody doing large sculptural works, may have a terribly unbalanced load in the kiln. This is especially true when the sculpture has a large heavy base and light weight top section. In those instances, it may be desirable to monitor and adjust the temperature in multiple locations within the kiln to achieve the perfect glaze firing. The Three Zone Temperature Controls works in conjunction with the Sentry 2.0 Digital Controller to monitor the kiln at 3 different locations within the kiln. If one region of the kiln is firing hotter (due to a lighter load of clay or kiln shelves in that area), the digital controller cuts the power to that region to allow the cooler or more heavily loaded regions to catch up. Thus, an unbalanced kiln load can be adjusted to fire at the same temperature throughout the kiln.
Sounds Nice.
But, there are serious draw backs to the 3 Zone Control system:
1) Temperature uniformity is nearly impossible to achieve at very low temperatures as the mass of the ware and kiln shelves readily absorb the small amount of heat produced by the kiln. Throw in the distribution of the shelves and temperature uniformity at very low temperatures can become an absolute screaming nightmare.
2) As air is heated in the kiln, the heated air moves through the kiln. Even a small pocket of slightly cold or hot air can be sufficient to trigger the system into engaging.
3) 3 Zone Control Systems operate by SLOWING down the zones that are firing too fast. This slowing down of the system is accomplished by shutting power to the relays controlling the elements in the fast firing zones. Speeding up the slower zone is not possible as kiln elements only operate at 100% capability. Therefore the only option is to shut off a section of the kiln.
4) The slowing down of the firing process combined with the serious temperature uniformity issues at low temperatures is not a good combination. Together, these two factors can add hours to the firing time as the kiln slowly increases in temperature, constantly shutting down one segment for the other segment to catch up. We realize that Speed is Not our Friend, but adding hours to the firing time to bump the temperature by 100˚F doesn't make much sense either.
5) At higher temperatures, the uniformity of the kiln chamber generally becomes far less of an issue as the air density has decreased and IR (Infra-Red) is the primary mode of energy transfer to heat the contents of the kiln. Even the most seriously unbalanced kiln load can be easily balanced through the use of the hold function built into the Sentry 2.0 Digital Controller at the end of the firing.
6) The 3 Zones are located in a single plane.... top, middle and bottom on one side of the kiln. The 3 Zone system was designed around the idea that kilns are unevenly loaded top to bottom. In reality a kiln could also be loaded unevenly front to back or left to right. The 3 Zone system does not address the practical issue of loading a kiln as evenly as possible (or the lack thereof).
| Single Zone S-Type Thermocouple shown in a Paragon Super Dragon on the right wall of the kiln chamber at the mid point (vertically) of the nearly 36" tall kiln chamber. |
7) In a standard tall kiln with a chamber height of 29" deep, the thermocouples of the 3 Zone Control system will be located approximately 8" apart (after vertically centering the middle thermocouple and allowing for the brick work and elements at the top and bottom of the kiln chamber). In a shorter (smaller) kiln, the spread between thermocouples will be even less. Distance between thermocouples is necessary for the 3 Zone system to detect temperature differences between segments... the shorter the distance, the less efficient the system will operate.
8) All 3 thermocouples must match in type (K versus S) and must be functional for the 3 Zone system to properly operate.
9) Price. Can't get around the fact that the 3 Zone Control system is expensive. For any Paragon Kiln, the 3 Zone Control, K-Type Thermocouple costs $130. The 3 Zone Control, S-Type Thermocouple costs a nice hefty $450.
Bottom line: the 3 Zone Controller can cause serious delays (increases in the firing time) in the firing of the kiln at very low temperature and is not the simplest means of correcting temperature uniformity issues near the end point of the firing process. Even if the 3 Zone Controller was beneficial at all temperatures, the failure to address the left to right or front to back loading issue remains a serious fault.
| So why do the kiln
manufacturers offer 3 Zone Controllers as an option (or in the case of
some kiln companies as standard equipment)? Because the technology
is readily available and it might
be of use to some customers. But, just because the product exists
does not make it useful or even a good value. Dogwood Ceramic Supply has evaluated the 3 Zone Control System and re-evaluated the system. We keep reaching the same conclusions.... because of the lack of correction for left versus right or front versus back loading issues, the additional cost of the system and the fact that the system can cause substantial increases to the firing time of the kiln, the 3 Zone system remains a very poor value and not useful to the vast majority of kiln buyers. For the micro percentage of customers who truly need the system (and they do exist), we will continue to offer the 3 Zone Control System. Because of limited desirability, the 3 Zone system is being removed as an regular option for the Paragon Kilns sold by Dogwood Ceramic Supply. If you truly need it, just ask, and we will request Paragon to add the 3 Zone system to your new kiln. |
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12590 Dedeaux Road
Gulfport Mississippi, 39503
Telephone (228) 831-4848 Fax (228) 831-3111
Showroom Business Hours:
Monday, Tuesday, Friday and Saturday 10AM to 5PM
Thursday 1PM to 6PM
Closed Wednesday and Sunday
The Three Zone Temperature Controls works in conjunction with the Sentry 2.0 Digital Controller to monitor the kiln at 3 different locations within the kiln. If one region of the kiln is firing hotter the digital controller cuts the power to that region to allow the cooler or more heavily loaded regions to catch up.