Using the combined temperature measurement from inside the ball and the gas temperature measurement from the exposed thermometer, a better idea of the temperatures personnel are experiencing can be made.
- The thermometers are not immersed sufficiently into the space whose temperature is to be measured. This results in a ‘stem error’ where the temperature on the cold side of the thermometer cools the stem of the thermometer on the hot side causing it to read low. A rough guide for the immersion length would be 40 X diameter of the thermometer or more.
- The thermometer is physically too large and hence slow to react to the temperature fluctuations it is subjected to.
- The thermometer is not placed in the optimum position.
- The thermometer mostly reads the temperature of the gases surrounding it and not the effect of the radiant heat.
The Combi thermometer is a development based on having a black ball that is about the size of parts of a human that are likely to get too hot, such as a hand or the back of the neck. The ball is coated in a high emissivity coating so it absorbs most of the radiant heat that impinges on it. Inside the ball is a fast response thermometer that measures the combined effect of the radiation and the local gas temperature to give a truer indication of what personnel would be experiencing. Attached close to the ball is another fast response thermometer that measures the gas temperature. Its job is to pick up any rapidly changing temperature such as a steam surge. The temperatures can be displayed locally or transmitted via WiFi to remote locations.