• Application: White goods (air conditioners, refrigerators, ovens, water heaters, BBQ ovens, etc.), industrial equipment (3D printers, machine tools, heaters, etc.), new energy (lithium batteries, solar panels, etc.), cold chain transportation, pipeline temperature measurement, etc.
• Temperature range: -40~+300℃, -55~+125℃, -200~650℃, -40~+1600℃, etc
• Chip: NTC(R value and B value), Pt100/Pt1000, DS18B20, thermocouple (K, N, E, J, T, S, etc.)
• Accuracy: NTC(1%, 2%), Pt100/Pt1000(AA/A/B), thermocouple (Ⅰ/Ⅱ), etc
• Shell material: stainless steel, brass, nickel plated copper, ABS, etc
• Shell structure and size: straight tube probe (diameter * length), thread probe (thread specifications: M thread, G thread, NPT thread, etc.)
• Cable material and length: PVC, TPE, silicone, stainless steel mesh braided cable, Teflon, glass fiber, PFA, etc.
• Wire terminal: hanging tin, pin terminals, U terminals, Molex, JST, RJ crystal head, navigation, etc.

• Common types of temperature sensors are: negative temperature coefficient thermistor NTC, digital sensor DS18B20, platinum resistance (Pt100/Pt1000), thermocouple (K, N, E, J, T, S, etc.).
• Choosing the right temperature sensor mainly considers the following points: temperature range, accuracy, output signal

• Types	NTC	Pt100/ Pt1000	DS18B20	Thermocouple
  Temp. range	-40~+300℃	-200~+650℃	-55~+125℃	-40~+1600℃
  Accuracy	±1%，±2%	±0.1/0.15/0.3℃	±0.5℃	Ⅰ：±1.5℃/±0.4%ltl Ⅱ：±2.5℃/±0.75%ltl
  Output signal	resistance	resistance	digital	mV

  
  
• When the temperature is below 300 ° C and the accuracy requirement is not high, choose an NTC temperature sensor.
• When the temperature or the accuracy is high, choose a platinum resistance temperature sensor.
• When the ultra-high temperature is above 1000℃ and the accuracy requirement is not high, the thermocouple temperature sensor is selected.
• When the temperature is within 100 ° C, the accuracy requirement is not high, and the data collection is convenient, the DS18B20 digital sensor is selected.

The most important factor in the selection of temperature sensor cables is determined by the temperature range. Cables of different materials are selected for different temperature ranges. The temperature range of common cable materials is as follows:

• PVC: -40~+ 80℃, -40~+105℃
• TPE: -50 ~+125℃, -55~+125℃
• Silicone: -50 to +200 ° C
• Teflon: -50 to 350 ° C
• Stainless steel: -50~+200℃, -50~+380℃, -50~+450℃
• Glass fiber: 450 ° C
• PFA: -200~+250℃

Platinum resistance has two wire system, three wire system, four wire system three wiring methods, the difference is as follows: 

• Two-wire system: The lead of a wire connected to each end of the thermal resistance temperature sensing element is a two-wire system. This lead method will bring in additional error of lead resistance, and the lead should not be too long in use. Generally suitable for occasions with low precision requirements.
• Three-wire system: Two leads are connected at one end of the thermal resistance temperature sensing element, and one lead is connected at the other end. This lead form is called the three-wire system. It can eliminate the influence of the inner lead resistance, and the measurement accuracy is higher than that of the two-wire system. The circuit to measure the three-wire platinum resistance is generally an unbalanced bridge, and the platinum resistance is used as a bridge arm resistance. When the bridge is balanced, the change of wire resistance does not have any effect on the measurement result, so the measurement error caused by the wire line resistance is eliminated (the premise is that it must be a full-arm bridge, otherwise it is impossible to completely eliminate the influence on the wire resistance). The use of three-wire system will greatly reduce the additional error caused by wire resistance, and the industry generally uses the three-wire system connection.
• Four-wire system: Two leads are connected to each end of the thermal resistance temperature sensing element. This lead form is called four-wire system. The four-wire measurement uses two additional test lines to provide a constant current, and the other two test lines to measure the voltage drop of the unknown resistance, so that if the input impedance of the voltmeter is high enough, the current hardly flows through the voltmeter, so that the voltage drop on the unknown resistance can be accurately measured and the resistance value can be calculated. Generally suitable for high-precision occasions.

A thermocouple is a conductor of two different materials welded together to form a closed loop, when the temperature of the two contact points is different, the thermoelectric motive force will be generated in the loop, this phenomenon is called the thermoelectric effect, the thermocouple is to measure the temperature by measuring the thermoelectric motive force.

NTC thermistor parameters are: resistance value, B value, dissipation coefficient, thermal time constant, resistance temperature coefficient.

• NTC thermistor resistance value: R [Ω]

The approximate value of resistance is: R2=R1exp[1/T2-1/T1]

R2: Resistance [Ω] at absolute temperature T2 [K]

R1: Resistance [Ω] at absolute temperature T1 [K]

• NTC thermistor B: B value [K]

The B value is a function of the change in resistance between two temperatures, expressed as: B= InR1-InR2 =2.3026(1ogR1-1ogR2)1/T1-1/T2 1/T1-1/T2

R1: Resistance [Ω] at absolute temperature T1 [K]

R2: Resistance [Ω] at absolute temperature T2 [K]

• Dissipation coefficient of NTC thermistor: δ [mW/℃]

The dissipation coefficient is the ratio of the electrical work consumed by the object to the corresponding temperature rise δ= W/T-Ta = I2R /T-Ta

δ : dissipation coefficient δ [mW/℃]

W: Electrical work consumed by thermistor (mW)

T: Temperature value after reaching thermal equilibrium (° C)

Ta: Room temperature [° C]

I: The current value on the thermistor at temperature T [mA]

R: The current value on the thermistor at temperature T [KΩ]

When measuring temperature, care should be taken to prevent the temperature rise of the thermistor due to heating.

l NTC thermistor thermal time constant: τ [sec.]

Under the condition of zero energy, due to the step effect, the temperature of the thermistor itself changes, and the time required for the temperature to change 63.2% between the initial value and the final value is the thermal time coefficient τ.

• NTC thermistor resistance temperature coefficient: α [%/℃]

α is the coefficient (that is, the rate of change) that indicates the degree of change of the resistance value for every 1oC change in the temperature of the thermistor α=1/R•dR/dT, the calculation formula is: α = 1/R•dR/dT×100 = -B/T2×100

α : resistance temperature coefficient (%/℃)

R: Resistance value at absolute temperature T [K] [Ω]

B: B value [K]

There are usually three calculation methods: lookup table method, Steinhart-Hart equation, and B-value method.

• Table lookup method: Each NTC has a corresponding R-T resistance table, which can be used to calculate the difference and find the temperature value corresponding to the resistance value.
• Steinhart-Hart equation: 1/T = A + B•ln(R) + C•[ln(R)]
• B value calculation method: R = R(25℃)•exp[B•(1/ T-1/298.15)]

Note: The NTC resistance curve is nonlinear, and the conversion resistance and temperature cannot be calculated according to the formula. And if you want to calculate through the formula, there are restrictions.

For example: the B value is usually calculated by 25 ° C and 50 ° C /85 ° C resistance, pay attention to the two temperature points, meaning that between 25 ° C -50 ° C /85 ° C, how much is the B value, in this temperature range, you can calculate the conversion resistance value and temperature through the B value, beyond the table or two points can only be worth the result.