The fundamental problem with surface temperature measurement is that it is subject to large stem conduction errors, also because heat conducted from the surface of the hot-plate causes a localised cold spot to be created which means that the temperature indicated by the hot plate is not necessarily the temperature at the point of measurement.
An ideal system would not disturb the heat-flux from the hot-plate.
During 1993 such a system was described (ref. “Progress in Contact Thermometry” 1993 B. D. Foulis) and Isotech have the inventors permission to make and market the device World-wide.
Principal of Operation
A fine wire type N thermocouple is used as the surface temperature sensor, a second junction 2 to 3mm along the thermocouple, senses the temperature difference due to heat flux along the sensor.
A heater heats the thermocouple stem until the temperature gradient is zero, thus creating a measurement without stem conduction, or disturbance of the hot-plate’s surface.
The 944 can be used with the Isotech Small Hot Plate model 983. A traceable calibration certificate is available to order.