In January 2012 we introduced the Thermistor hash command, which makes the use of spreadsheets largely unnecessary. SPLat/PC can now do all the hard work for you.

The first step in the procedure of designing your temperature measurement system is setting the temperature range and specifying the thermistor.

It might appear that selecting the temperature range to be measured is fairly self-evident. Not necessarily! If you want a good result you need to narrow down the temperature range as far as you possibly can. The reasons for this are:

Lower limit too low

The low temperature limit is the main “driver” for the feed resistor Rfeed and/or the feed voltage Vfeed.These in turn determine the resolution of the temperature measurement. This is the most important limit to not over-specify.

Temperature range too large

The larger the temperature range the more pronounced the thermistor nonlinearity will be. This in turn means the polynomial equation (which is always an approximation!) will become less accurate, and accuracy may suffer.

The first step in the process is therefore to set the minimum and maximum temperatures.You can enter your values in the spreadsheet in the green Tmin and Tmax cells.

Don’t worry if entering these numbers causes errors in the sheet. That will all get sorted out later.