PT100 linear temperature sensor using method - — To continue

What is the meaning of linearity?

linearity is describe sensor output voltage with the temperature change of the degree of linear, in fact, that is, the sensor output voltage in working temperature range relative to the maximum deviation of ideal fitting line. In general, the linearity of the typical values for plus or minus 05%, it is clear that the sensor linearity is higher ( The smaller the value) For the design of the instrument is more simple, completely in the input stage of instrument without using linearization. Why is linear temperature sensor standardization output?

the so-called standardized output, is at 0 ℃ temperature sensor on the regulation of working conditions, the output voltage is limited to a small range, although do not swap, only limited in 690 - the benchmark voltage value Between 710 mv, so in the circuit design, easy to mastery of the output of the sensor in the macro, in both the bridge circuit design and temperature compensation, as long as in the 690 - 710 mv, make a few adjustments in the debugging. And unlike ordinary thermistor due to different models, the resistance is different also, in view of the different models, require different design calculation. So the standardization of the linear temperature sensor output, can make the instrument standardization design the circuit. The user how to test linear temperature sensor?

the user after the purchase of sensor, but under the condition of constant current, according to the size, the temperature using two or three test, to test swap accuracy, linearity and temperature coefficient. In general, the most simple test methods as long as the inspection reference voltage value. And all electrical parameters, at the time of delivery with goods parameter table ( Certificate of approval) To provide the number of sensor parameters in detail.

conditions of the test has the following requirements:

constant-current source: 100 mu A, plus or minus 05%.

thermostatic temperature field: volatility: + 005 ℃ or less;

instrument: 412 or 512 digital voltmeter. Actual use temperature sensor constant-current power supply must be used?

in general is unnecessary, constant-voltage power supply can completely bridge road ( See figure 1, figure 2) 。 This is because under the condition of current of about 100 mu A, the temperature of the sensor - Voltage conversion coefficient of variation is small, can give an order of magnitude of the measured concept:

S = - in the 100 mu A 2 ℃ mv

S = - when 40 mu A 21 ℃ mv

S = - in the 1000 mu A 19 ℃ mv

and constant voltage power supply in the actual Bridges, the electric current won't have such a large amplitude.

when constant voltage power supply, how do you determine the sensor load resistance value?

when constant voltage power supply, load resistance between power supply and sensor anode, between the positive and negative output signal from the sensor, design of resistance R, with sensors at 0 c working current is 100 mu. Such as sensors of reference voltage V ( 0) （ mV） , constant voltage source to VDD ( mV） , R = ( VDD - V（ 0) ） ( mV) 01 ( mA) 。 To calculate the resistance R, if there is no this kind of resistance, the actual resistance could be selected to the nearest value, has no effect on temperature measurement accuracy. Linear temperature compensation element for temperature compensation circuit have what advantages?

this is mainly consider the output of the thermal sensor standardization and the regulation of temperature coefficient, easy to design. In addition, due to temperature coefficient with the transistor circuit of the transistor base and emitter voltage temperature coefficient, the same as the working point of stable transistor circuit base drift element is very appropriate. And a few components in series, may, by way of parallel potentiator by potentiometer to adjust the different temperature coefficient, in order to realize accurate temperature compensation function, See figure 3) 。 The temperature coefficient of adjustable compensation elements, need not multifarious design, working current has no strict requirements for components, this is also the one of the great strengths of linear temperature sensor used for temperature compensation. The stability of the mean?

stability refers to the reference voltage value in sensor drift, the drift amount according to the temperature - Converted into temperature voltage conversion coefficient, namely stability = + delta VS. The stability of linear temperature sensor to + 005 ℃ for years. The parameters describing the sensor under the condition of all sorts of use's ability to keep the original features. Long-term transmission of sensor signals have effect?

say, normally transmission distance up to 1000 meters. If the distance is further, sensor output signal can be considered in the local conversion to digital quantity, so that we can easily realize long distance transmission.

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