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