PT100 of commonly used platinum thermistor is one kind is had the feeling lukewarm sensor of temperature coefficient, lift along with temperature namely, value of sensor oneself block shows the change that positive involves, if pursue 1, the temperature of the object that be measured every rise 1 ℃ , the block value of PT100 increases 0.385Ω subsequently, be in – inside the interval of ℃ of 200 ℃ ~850, the degree of linearity with platinum thermistor good PT100, for developer development provided the safeguard that high accuracy measures, this is one of accounts with PT100 comprehensive application.

 

Curve of graph 1 PT100

 

PT100 can measure lukewarm sensor as high accuracy, the function is exceedingly good, but in industrial environment complex case falls, the lead with long sensor can bring line impedance, this to 0.385Ω/ ℃ , if want to assure 0.1 degrees precision, the error that needs to make sure line impedance is drawn namely must be less than 38.5mΩ , and the error that brings to do not introduce fuel factor of sensor PT100 oneself, the electric current of constant current source of PT100 is installed commonly in 0.1mA~1mA, if constant current source is installed in 1mA, by type 1.1 computation can be gotten, error voltage must be less than 38.5uV, this is the estimation that eliminates noise influence to fall.

 

(1.1)

 

Accordingly, want to get high accuracy measures lukewarm effect, the error that must eliminate sensor line impedance to bring is affected, general wiring has 3 kinds of kind inside the industry, if express 1.

 

Watch 1 PT100 is general receive a standard

 

By the watch 1 can see, two lines are made receive normal impedance error the biggest, and cannot eliminate; 4 lines are made receive a law to also weigh Er article family name to receive a standard, most essence of life is accurate and simple, but need interface resource is more; 3 lines are made receive a law to be able to eliminate line error through computation, managing interface resource, but need the impedance such as 3 lines, this also is easier implementation.

 

Be aimed at complex industrial environment, the client measures the demand of lukewarm product to high accuracy, ZLG sends far electron to roll out segregation of PT100 of thermal resistance of high accuracy of a double passageway to measure lukewarm module TPS02R, can come true in – precision is measured to be 0.02%±0.1 ℃ inside the interval of ℃ of 200 ℃ ~850, 10ppm low temperature bleachs index.

 

Graph 2 3 lines are made receive a law to apply

  

If pursue 2, 3 lines are made receive a law to collect voltage signal, provide gain amplitude by back end PGA, via ADC modulus changeover, output number signal gives MCU processing, as a result of A, b, c3 line all puts online impedance RL1, RL2, RL3. Installation standard can be adopted here 3 lines make PT100, can assure:

 

(1.2)

 

Classics of constant current headstream in all modular resistor R, it is certain to be offerred for ADC in all modular voltage, ADC differs cent to input a passageway to measure AB respectively, two end of AC voltage, . Foregone:

 

(1.3)

 

Combine form 1.2, through computational processing:

 

(1.4)

 

Through type 1.4, can get elimination the PT100 measured value of line impedance error completely, temperature of implementation high accuracy is measured. 3 lines are made receive a law to be able to be made with 4 lines in implementation identical measure precision while, save a terminal of a wiring, this is very big to developing miniaturization product advantage to the user, 3 lines are made receive a law to want to assure A only, b, the impedance such as C, the introducing that can assure line impedance the error can be ignorred basically.

 

ZLG sends far electron TPS02R to make the foundation that receives a standard go up in 3 lines, do to constant current source optimize processing, use carry to put negative feedback principle, increase stability of constant current source, it is certain to be offerred for ADC input in all modular voltage, for ADC poor cent is measured offer assure, gift the warning function that monitor. Specific if express,measure data 2.

 

Watch 2 ZLG measures data of lukewarm plan test and verify