Designing a thermistor temperature sensing device can be challenging if you plan to use it over its entire temperature range. A thermistor is typically a high-impedance, resistive device, so it can simplify one of the interface issues when you need to convert the thermistor's resistance to a voltage value. A more challenging interface issue, however, is how to capture the thermistor's nonlinear behavior digitally with a linear ADC.
The term "thermistor" comes from a generalization of the description "heat{{0}}sensitive resistor". Thermistors include two basic types, positive temperature coefficient thermistors and negative temperature coefficient thermistors. Negative temperature coefficient thermistors are ideal for high-precision temperature measurement. To determine the temperature around the thermistor, you can do it with the help of the Steinhart-Hart formula: T=1/(A0 plus A1(lnRT) plus A3(lnRT3)). Among them, T is the temperature in Kelvin; RT is the resistance value of the thermistor at temperature T; and A0, A1 and A3 are constants provided by the thermistor manufacturer.
Athraíonn friotaíocht an teirmeastair le teocht, agus níl an t-athrú seo-líneach, mar a léiríonn foirmle Steinhart-Hart. Agus tomhais teochta á ndéanamh, ní mór sruth tagartha a thiomáint tríd an teirmeastar chun voltas coibhéiseach a chruthú a bhfuil freagra neamhlíneach aige. Is féidir leat iarracht a dhéanamh cúiteamh as freagra neamhlíneach an teirmeastair tríd an tábla tagartha a thugtar ar an micrea-rialtóir a úsáid. Fiú dá bhféadfá algartam den sórt sin a rith ar an bhfirmware microcontroller, bheadh tiontaire ardchruinneas ag teastáil uait fós le haghaidh sonraí a ghabháil i láthair teochtaí foircneacha.
Alternatively, you can use a "hardware linearization" technique and a lower precision ADC before digitizing. (Figure 1) One technique is to place a resistor RSER in series with the thermistor RTHERM and a reference voltage or power supply (see Figure 1). The PGA (Programmable Gain Amplifier) is set to 1V/V, but in such a circuit, a 10-bit precision ADC can only sense a very limited temperature range (about ±25 degree ).
Figiúr 1, tabhair faoi deara nach bhfuil an réigiún teocht ard réitithe i bhFíor 1. Ach má mhéadaítear gnóthachan an PGA ag na luachanna teochta seo, is féidir comhartha aschuir an PGA a rialú laistigh de raon inar féidir leis an ADC iontaofa a sholáthar. tiontaithe chun teocht an teirmeastair a shainaithint.
Léann algartam braite teochta an fhirmware microcontroller an luach digiteach ADC cruinneas 10-giotán agus aistrítear é chuig gnáthamh bogearraí hysteresis PGA. Fíoraíonn gnáthamh hysteresis PGA socrú gnóthachan PGA agus déanann sé luach digiteach ADC a chur i gcomparáid le luach an nód voltais a thaispeántar i bhFíor 1. Má sháraíonn an t-aschur ADC luach an nód voltais, socróidh an microcontroller gnóthachan PGA go dtí an chéad cheann eile níos airde. nó socrú gnóthachan níos ísle. Más gá, faigheann an microcontroller luach ADC nua arís. Ansin cuirtear an gnóthachan PGA agus luachanna ADC ar aghaidh chuig gnáthamh idirshuímh líneach píosa ar an micririalóir.
Getting data from a nonlinear thermistor is sometimes seen as an "impossible task". You can use a series resistor, a microcontroller, a 10-bit ADC, and a PGA to solve the measurement problems of non-linear thermistors beyond ±25 degree .
