Kiln Pyrometer


Figure 1. The Model 307 Digital Pyrometer

The studio has a CIE Model 307 battery powered, digital pyrometer that connects to the type K thermocouples installed in both downdraft kilns. (Click on photo to enlarge.) The unit reads to 1300 C (2372 F) with a worst-case accuracy of ± 0.5% + 1°C.  The F/C key (2nd row, left) switches between the Fahrenheit and Celsius temperature scales; note the scale letter “F” or “C” is displayed just above the rightmost temperature digit. The unit also has a 0.1/1 key (top row, right) to select display resolutions to either one degree, or to a tenth of a degree. Figure 1 shows a 64°F temperature displayed to a “1°” resolution; it would have read 64.2°F, for example, for a “0.1°” resolution. 

The pyrometer indicates conditions outside its operating limits by displaying the default message OL, or “Over Limits”. More on that below.

Click on this link for complete specifications and the manufacturer’s operating instructions:…. Model 307 Owner’s Manual

Connecting the Thermocouple
Each kiln has one temperature probe (thermocouple) installed in its sidewall near the top. Take the probe wiring from the selected kiln and insert the yellow end-plug into the pyrometer T1 Input with the probe wire UPWARD in the manner pictured in Figure 1. The upward orientation of the wire is very important because the two prongs in the plug are different widths, and can damage the pryometer if inserted backwards. Push the T1 key, and the current temperature at the probe tip will be displayed. 

The display shows a small battery symbol (on the lower right) when power is low. It does so in enough time to install a new battery during the firing. The readout gets dimmer very slowly as power drops down. The pyrometer takes a standard 9 volt battery. They are sold at Gourmet Heaven if one is not available in the tool cabinet.
To change the battery, remove the three screws on the back of the unit and pull the plastic chassis away. A correct size phillips screwdriver is stored in the pyrometer box. Once opened, you’ll see that the battery can be removed by hand. Make note of how the battery is oriented, and be sure to install the new one in the exact same way.

OL Conditions
 Temperature data is not displayed when the pyrometer senses an OL condition. OverLimit conditions occur for three primary reasons:

  1. Display Limit: The pyrometer can only display numbers below 2000. So, for instance, 1999 F is as high as it can read before mandatorily switching to the Celsius scale. If kiln temperature exceeds 1999F and the F/C switch has not been pushed, then the display will indicate OLPushing the F/C key will restore operation with celsius readouts from there on. 
  2. Resolution Limit: The display reads OL if the readout exceeds 99 without the 1/0.1 Resolution Switch being pressed. Pressing the 1/0.1 switch lowers the resolution to degrees from tenths of a degree. After pressing the switch, indications are rounded to the nearest whole number degree.
  3. Continuity Limit: The unit will display OL if the thermocouple probe is open circuit. Once the firing has started, there is very little you can do about a break in the wiring since the probe is too hot to touch. So….before the firing, it’s best to plug in the probe and turn on the pyrometer to make sure everything is reading correctly, and that battery power is not low.

If the pyrometer still reads OL when limits 1) and 2) above are checked and within bounds, then the most probable cause is that the thermocouple tip has oxidized/rusted to the point continuity has been lost. In order to correct that, pull the probe out of the kiln and clean/sand/brush/rewind the tip until the unit starts reading temperature again.

Be sure to push the On/Off switch after a firing in order to turn the pyrometer OFF.  If forgotten, the battery will go dead before the next firing. 




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