Why does the temperature read-out on my hand-held pyrometer differ from the temperature shown on the DynaTrol?
- In order for temperature readouts to be close to each other, the two devices need to use the same type and style thermocouples. Additionally, they need to be put into the same area and to the same depth in the kiln.
- The type of thermocouple is "Type K" or "Type S". In this country, type K will use red (-) and yellow (+) leads. Type S in this country uses red (-) and black (+) leads. Type S and K thermocouples are not interchangeable, except by replacing all the thermocouple wiring and resetting or replacing the kiln controller.
- The style of a thermocouple has to do with things like the thickness of the wires in the actual thermocouple, if there is a ceramic or metal sheath over the thermocouple, or no sheath at all, etc. In other words, the thermocouples need to be identical. For example, a thicker wire thermocouple will read a given temperature as being cooler than a thinner wire thermocouple. The reason for this is that the thicker wires draw more heat off of the thermocouple tip than thinner wires can. Less heat on the tip results in a lower temperature reading on the display.
- The differences in type and style can account for quite a bit of temperature deviation between different devices- sometimes hundreds of degrees. Even if the thermocouples are the same, it is still possible to have different temperatures on the two devices. The radiant heat that is hitting one thermocouple may be greater than or less than the radiant heat that is hitting another thermocouple. For example, if a flat surface of a piece of pottery was right in front of a thermocouple all the radiant heat from the elements there would be reflected back into the space where the TC tip is. If it is not like this on all the thermocouples, then there will be a temperature difference between them.
- If you are getting different temperatures regardless of what you try, you will have to fire a program and see at certain temperatures what the two different devices read. You will use this info to make a chart. Ultimately the chart would be organized to show that, for instance, at 300F the corresponding temp is 287°F, or at 2145°F the corresponding temp is 2086°F. etc. The difference in the readings between devices is probably not the same at different temperatures.
November 21, 2024
