Platinum Resistance Thermometers and Self-Heating Effect
• Platinum resistance thermometers have a ceramic sensing element at the tip of the sheath.
• The sensing element contains fine platinum wire coils to prevent shorting during heating/cooling.
• Resistance is measured using a temperature measurement device, passing a known current through the sensing element and developing a voltage across the sensor.
• Resistance (Rt) is calculated using ohms law, where tE is the temperature due to the environment being measured and?tSH is the additional temperature increase due to the self-heating effect.
• Two measurements are made: one with normal measuring current and one with a current that either halves or doubles the power.
• The magnitude of self-heating depends on factors like the size of the current, nominal resistance, thermometer construction, and thermal contact with the environment.