I acquired some 100k¦¸ 1.6mm glass bead thermistors of the type used in 3D printers for a flow soldering project, but the manufacturer¡¯s characteristics were not available. ?0¡ãC and 100¡ãC temperatures are fairly easily established at sea level with ice and water, but it would have been be messy to set up an oil bath or similar.?
A piece of 3.5mm aluminium bar approximately 23 x 15mm was drilled in two places approximately 5mm apart on the narrow edge to a depth of 15mm as pockets for the thermistor and a type K thermocouple and held by a ¡°third hand¡± clip by the wires so that hot air from a de-soldering tool could be applied safely.? The thermal mass of the bar was sufficient to allow the temperature and corresponding resistance to be measured repeatably.? The bar was heated to a number of temperatures at 20 degree intervals as indicated by the thermocouple and the resistance recorded.? On plotting out and comparison with a number of Arduino library results [1] the thermistor was found to be very close to the Type 1 characteristic.
Measurement accuracy is maybe 1-2% at 200¡ãC, good enough for my purposes, and may be useful to others.
PeterS? G8EZE
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[1] ?? ???? The tables are expressed as counts scaled 0-1023 on a 5V ADC
