# Thermistor hash command

The Thermistor hash command makes it very easy to program for NTC thermistor temperature sensors.

Do not confuse thermistors with thermocouples or RTD sensors. The Thermistor hash command applies to NTC (negative temperature coefficient) thermistors, and nothing else.

Circuit configuration

The Thermistor hash command assumes the following circuit configuration, which is used in a large number of standard and custom SPLat controllers.

Example:

   fAnIn        0    ;Raw thermistor voltage to W
   #Thermistor  Params(10000, 3840) Feed(5.6, 5, 50000) RangeC(-25, 50) Order(5) ;temperature now in W

The various hash functions are explained in the rest of this section.

How it works

When SPLat/PC encounters the Thermistor hash command during program translation, it uses the values supplied in the associated hash functions to calculate a table of raw analog reading versus temperature. It then processes the table to produce a best fit polynomial, and stores the polynomial coefficients in an NVEM0 table. When your SPLat program later wants to convert a raw analog thermistor reading to temperature, the raw reading is "fed into" the polynomial and converted to temperature. In effect, this process automates the older procedure given in the thermistor temperature measurement tutorial.

The result screen and sandbox

If the Thermistor hash command line includes a Display hash function, SPLat/PC will pop up a special window that shows the results of its internal calculations. This window includes a sandbox function, that lets you experiment with different values and generate a modified Thermistor command line.

Selecting a thermistor

There are no hard and fast rules for thermistor selection, but here are some pointers.

We are in no way associated with any of the above referenced resources and take no responsibility for their accuracy.

Don't equate the thermistor accuracy with the final measurement accuracy you will achieve! There are many other sources of error that cannot be controlled as easily as just paying out a few more dollars for the thermistor. The main benefit of buying a very high accuracy thermistor is interchangeability.

The thermistor hash command does not set the thermistor drive voltage. On the MMi202 and SL100 you need to initialise the thermistor drive voltage yourself.

MMi202 thermistor drive voltage SL100 thermistor drive voltage (Look near the bottom of the respective pages)