Recently this temperature test has been used PT100, Pt1000, and a thermocouple, to roughly summarized here.
1, pt series
precision pt100 and pt1000 compared finer 1000, after he a greater resistance value. Two resistors are a graduated table, corresponding to 0 degrees PT100 is 100 ohms, Pt1000 is 0 degrees corresponding to 1000 ohms, resistance it will vary with temperature changes. 1000 PT after it means that at 0 ℃ resistance of 1000 ohms at 300 ℃, its ohmic resistance is about 2120.515. Its industrial principle: When PT1000 at 0 degrees Celsius when its resistance is 1000 ohms, its resistance will increase its resistance as the temperature is increased up to the uniform.
There are two methods according to the resistance temperature requirements: look-up table and the calculation method. Fast look-up table calculated relative speed method, but accuracy is low, and takes up a certain amount of program space. If the temperature high precision and limited resources, program memory, preferably by calculation.
I currently use, basically demand temperature by calculation, of course, that to make the temperature - resistance calculation formula, thereby calculating the voltage, temperature backstepping.
pt1000 temperature - resistance of the formula: Rt = R * [1 + At + Bt² + C (t-100 ℃) t³]
where:
A = 3.9083 *. 3 E-
B-E. 7 = -5.775 *
C * = -4.183 e-12
I have a project is to take Rt = R * [1 + at ], because the microcontroller calculates Root number, certainly more time-consuming, and this does not require high precision, in the range of 200 degrees, the deviation or relatively small, but if the temperature is high to be measured, it is still optimized for electrically and formulas.
2, the circuit
after pt1000 difference with the sampling bridge circuit to measure the voltage at one end of a substantially constant, temperature change, then the voltage output will change pt1000, op07 amplifying the amount of change, the feed can be obtained in response to sampling adc voltage value, the temperature can be calculated based on the voltage value.
Is also useful to direct pt100 and a resistor in series, calculated in terms of partial pressure temperature, this way at temperatures ranging from relatively small, there may be a good precision, substantially less than 0.5 degrees.
3, a thermocouple
thermocouple test mode is not the same as above, but basically properties of the metal varies with temperature, but platinum RTD thermocouple differentiated, platinum thermal resistance is the resistance of R changes, the thermocouple is a hot spot effect, according to two different metals for different reaction temperatures, the thermoelectric power generation, of course, have reference to the cold end, as is generally calculated to freezing, many integrated circuits have been simplified thermocouple of design, direct calculation of the temperature voltage can be obtained. And pt100, Pt1000 is often required to take their own circuit, calculates, of course, high-precision pt100 ADI has simplified design and the like.