PTCR Temperature Measuring Rings

Process Temperature Control Rings PTCR (Ferro), 15 pieces

Process Temperature Control Rings, or PTCR for short, are a reliable tool for determining the actual heat input at any given point in a kiln. Unlike a thermocouple, which only records the instantaneous temperature at its tip, the ring records the so-called "heat work," which is the combined effect of temperature and duration. This exact value determines whether the body and glaze mature properly. The ring absorbs all forms of heat that reach it: heat conduction, thermal radiation, and convection. This makes it ideal for troubleshooting and quality assurance, for example, to detect temperature differences within the firing chamber or to cross-check electronic controls.

What's included: Each pack contains 15 rings of the selected type (dimensions per ring approx. ø20 x 7 mm, approx. 43 g per pack).

Functional principle: Measuring via shrinkage

During the firing, the ring shrinks in proportion to the heat input it receives, and its color also changes. The extent of the shrinkage depends on the kiln temperature profile, heat conduction conditions, and the dwell time in the kiln. Therefore, the more heat the ring absorbs over the entire firing duration, the smaller its outer diameter becomes. From this final diameter, the nominal temperature for the entire heat process can be derived after firing.

How to measure the ring

After cooling, the outer diameter of the ring is determined using a digital caliper. A measurement accuracy of at least 0.01 mm is important, as even small differences in diameter indicate significant temperature differences. The measured value is then looked up in the supplied conversion table, which assigns a nominal temperature to each diameter. This provides a verifiable check of the firing process even without an internal kiln display.

Placement in the kiln

The ring is simply placed in the firing chamber at the point to be tested and can be placed directly on the kiln shelf. However, place it on a small amount of kiln wash so that it does not adhere during firing. Since the ring can be placed freely, individual shelves, edge zones, or the kiln core can be specifically checked.

Choosing the right ring type

Each ring type covers a specific temperature range. Choose the type so that the maximum temperature of your firing process is approximately in the middle of the specified range, as this is where the ring works most accurately. Four types are available in the selection menu:

The types overlap intentionally, so that multiple rings are usually suitable for common firing schedules. If your target temperature is in the transition range of two types, choose the one for which your target temperature is closer to the center.

Heating rate and hold time

The values provided in the tables apply to a heating rate of approximately 120 °C/h in the upper temperature range. Since the ring measures heat work and not pure temperature, a different heating rate will affect the result: if the kiln is heated more slowly or the final temperature is held for a period of time, the ring will absorb more heat and shrink more. Therefore, take longer holding times into account during evaluation.

Oxidation and reduction

In an oxidation firing with a normal air atmosphere, the rings are ready for immediate use. For reduction firings as well as firings under vacuum, the rings must be pre-fired in air beforehand; otherwise, the altered atmosphere will distort the measurement result. A proven pre-firing schedule: heat to 550 °C in approximately 275 minutes and hold for 60 minutes.

Practical tip: Mapping the temperature field

Do not use just one, but several rings at different points in the kiln, such as on the top, middle, and bottom shelves, as well as near the door and in the back area. After firing, the different diameters show at a glance where the kiln fires hotter or colder. This allows temperature differences to be made visible and corrected specifically, long before they affect the firing result.

PTCR or Seger cones?

Both tools measure heat work but are intended for different purposes. The PTCR ring provides a numerical temperature value via exact shrinkage measurement and is therefore particularly suitable for precise troubleshooting and mapping the temperature field at several points in the kiln. Seger cones, on the other hand, show the reaching of a target temperature directly in the kiln and are the quick, easy-to-read choice for ongoing firing control. In many workshops, both complement each other. Seger cones can be found here: Orton Seger cones

Safety information

Classification according to GHS: GHS08 (Health hazard). Please observe the usual precautions when handling ceramic materials, especially avoiding dust. We will provide the safety data sheet upon request.

If you have any questions regarding type selection or evaluation, we are always available to help. Just send us a message using the contact form below and you will get a reply by the next day at the latest.