KNOWLEDGEBASE

What is an Automatic Control Box?

Similarity of Automatic Control Box with Manual Control box

  1. The similarities between the automatic controls and the manual controls are most easily seen in the power circuits.
  2. Just like in a large manually-controlled kiln with contactors controlled by switches, all the automatic kilns contain contactors which are controlled by the automatic controller.
  3. Early controls just had one output which turned all the contactors (as well as the elements) on and off together.
  4. Later controls (used after September 1998) typically have 3 inputs and outputs, which allows each contactor, and the element circuit connected to it, to be turned on and off individually as needed, based on the various inputs.

Signals from the thermocouples tell the control what to do

  1. The control knows when to turn the contactors on and off because of the signals it receives from the inputs.
  2. The inputs are the thermocouples (TCs), also known as the temperature sensors.
  3. In early controls only one TC was used.
  4. The micro-processor (the brain) in the control compared the TC reading to the map of the programmed firing it was following and decided whether to activate the output to turn on all the elements or not.
  5. The later versions of these controls, like our DynaTrol, have three of these thermocouples inputs. Each is connected to its own part of the processor and has its own separate output.
  6. The thermocouples are meant to be positioned in the wall of the kiln near the middle of the zone whose temperature they are reading; the tips should be about 1” to 1-1/2” in.

Zones

  1. A zone is the area in a kiln controlled by just one of the controllers outputs. For example, a model JD230 has three zones, each controlled by one of the three main outputs.
  2. In its control panel there are three branch circuits, each containing a contactor.
  3. Branch circuit number one's contactor is controlled by output number one from the DynaTrol controller. Output number one comes on or off depending on readings from thermocouple number one (input number 1), which is located in the top (#1) section of the kiln. The electricity in branch circuit number one feeds the elements in the top section (number one zone).
  4. Number two zone is the middle section and number three zone is the bottom section; each is individually controlled by their respective contactors and thermocouples.
  5. Essentially, each zone is like its own kiln, with its own temperature sensor and power supply. When stacked on top of each other the zones operate independently, yet they all follow the same path and more or less do the same thing by comparing the actual temperature in each zone to what is on the program map and then either leaving the elements on or turning them off accordingly.
  6. The DynaTrol computer-controlled kilns use calculations to determine some functions. These calculations are performed in the micro-processor with data fed from your choices in programming, the thermocouples and its the internal clock.
  7. The various calculations performed throughout the firing result in the complex firing programs, uniformity and the consistent automatic shut-off or controlled cool down.  Your choices in programming fill in the blanks on the map of the firing (i.e. how fast the kiln will climb in temperature and to what temperature, if there is a hold, a preheat, a delay, etc).
  8. The Easy Fire programs have most of these settings pre-programmed.
  9. The Vary Fire programs can be completely programmed and altered as you wish.
  10. The thermocouples measure the temperature in the kiln by emitting a specific linear millivolt signal for each degree of temperature. The microprocessor equates this millivolt signal to a specific temperature in °F or °C.
  11. The location of each thermocouple is important because the signal emitted will reflect the temperature in that part of the kiln. The DynaTrol takes these signals (typically one from the top zone in the kiln, one from the middle zone, and one from the bottom zone) and compares each in turn to the “process variable” or “setpoint”. This is the temperature that the kiln is supposed to be at any particular point in the firing program. This “point in time” is constantly being modified as time passes.
  12. Based on where the firing map says the kiln should be, the appropriate corresponding outputs to the TC inputs are activated. In other words, when each TC reading is compared to the firing map, a decision is made by the micro-processor to either turn on the elements in that particular thermocouple's section, or to turn them off. In this way, the kiln temperature closely follows the programmed rises, holds and ramp-downs.
  13. The internal clock is really never seen except when the control is counting down hours and minutes during a hold time, a preheat or a delayed start. However, its information is used in nearly every calculation.
  14. The Orton Firing Institute has devised and patented a way to calculate a final temperature for a firing, based on the relationship between how many degrees the kiln is climbing per hour, and what temperature is presently in the kiln. This calculated final set point temperature is the temperature at which the pyrometric cone that the firing has been programmed to go to will melt, given that specific rate of climb and current temperature. Near the end of firing, the DynaTrol slows the kiln's rate of climb down proportionally in order to avoid an overshoot. This means that the calculated final temperature is constantly being adjusted at the end of the firing to account for the slowing down of the kiln. This is only used in the “Easy-Fire” mode.
  15. It is an elegant way for the control to measure heat-work that is so important for ceramic firing and consistently and accurately fire correctly even given different loading conditions and the changing character of the kiln itself.

Diagnostics

  1. Needless to say, these controllers are more complicated than the older infinite or Hi-Medium-Low switches. In order to properly control the kiln, they also need a lot of self-diagnostics.
  2. If a thermocouple is burned out there needs to be a way to alert the user.
  3. If the kiln is climbing so slowly that the calculations reach an impossible scenario, there must also be a way to alert the user.
  4. All the error codes are explained in Appendix G of the DynaTrol Instructions (dynatrol-instruct-blue.pdf). They all refer to a specific situation, but the reasons that the situation exists is often due to more than one different cause.

Calibrating the control

  1. See the section on calibrating the control in basic-dynatrol.pdf. There is a good explanation of the thermocouple offsets and how to change them.