The main problem of the thermistor when used1

Thermistor is a kind of sensitive element, has been widely used in industrial application. Users in the process of using a thermistor also can appear some problems, we need to master for some common problems are, so you can better use of thermistor. Engineering today is to introduce specific thermistor for everyone to use common problems, hope you can help to you.

if you intend to use all over the whole temperature range thermistor temperature sensor parts, then the device design work can be challenging. Thermistor is usually a high impedance, resistive device, so when you need to convert the thermistor resistance to voltage, the device can simplify a interface problem of them. More challenging interface problem is, however, how to make use of linear ADC to capture the nonlinear behavior of the thermistor in digital form.

the word 'thermistor' from the 'heat sensitive resistor' generalization of this description. Thermistor including two basic types, respectively as the positive temperature coefficient thermistor and negative temperature coefficient thermistor. Negative temperature coefficient thermistor is very suitable for high precision temperature measurement. To determine the temperature around the thermistor, you can use Steinhart - Hart formula: T = 1 ( A0+A1( lnRT) +A3( lnRT3) ) To implement. Among them, T as the kelvin temperature; RT for thermistor temperature T resistance; The A0, A1 and A3 is provided by the thermistor manufacturer constant.

the thermistor resistance changes with the change of temperature, and this kind of change is non-linear, Steinhart - Hart formula shows that. When the temperature measurement, thermistor reference need to drive a current through, to create a equivalent voltage, the equivalent voltage has a nonlinear response. You can use on the micro controller equipped reference table, try to compensate for the nonlinear response of thermistor. Even if you can run on the microcontroller firmware such algorithms, but you still need a high precision temperature converter used in case of extreme value for data capture.

another way is that you can use 'linear' hardware before digital technology and a lower precision of ADC. ( 图1) One was a technique to a resistor RSER with thermistor RTHERM and reference voltage or power supply in series. The PGA ( Programmable gain amplifier) Set to 1 vv, but in this circuit, a 10 precision ADC can only induction limited temperature range ( About 25 ° C + / -) 。

the Figure 1, please note that in Figure 1 for high temperature could not parse. But if under the temperature increase the gain of PGA, PGA output signal can be controlled within a certain range, within the scope of the ADC conversion can provide reliably, and the temperature of the thermistor for identification.

the microcontroller firmware temperature sensing method can read 10 precision of ADC digital value, and send it to the PGA lag software program. PGA lag program will check the PGA gain Settings, and the ADC digital value and figure 1 shows the value of the node voltage comparison. If the ADC output more than the value of the node voltage, the microcontroller will PGA gain setting to the next higher or lower gain Settings. If necessary, the microcontroller will once again to get a new ADC values. Then PGA gain and ADC values will be transferred to a micro controller piecewise linear interpolation procedure.

to get the data from the nonlinear thermal resistor is sometimes seen as a 'mission impossible'. You can put a series resistance, a micro controller, a 10 bit ADC and a PGA and reasonable, in order to solve nonlinear thermistors after more than + / - 25 ° C temperature measurement problem.

more high-quality sensors at https://www. rtdcn。 Com /

key words: thermal resistance, thermocouple, thermal resistance, platinum resistance, PT100, PT1000, pressure sensor and digital temperature sensor