PT100 temperature sensor principle, fault and its processing method

First, the principle of PT100

basic principle: PT100 is a kind of temperature sensor, when resistance (resistance temperature sensor RTD,电阻温度探测器) - a kind of material made of resistance, it will change its resistance increase with increasing temperature, if it also follow up along with the rising of temperature resistance and is called the resistance coefficient, if it along with the rising of temperature resistance decline is called negative resistance coefficient. Most of the resistance temperature sensor is made of metal, with platinum ( Pt) Resistance temperature detector, the most stable - acid and alkali resistance, no deterioration, fairly linear, the most popular industry.

PT100 temperature sensor is a kind of platinum ( Pt) Resistance temperature sensor, belongs to the resistivity, its resistance and the relation between the temperature changes are as follows: R = Ro ( 1 +αT)

with alpha = 000392, Ro 100 Ω ( In the resistance value of 0 ℃) , it is Celsius temperature T, therefore made of platinum resistance temperature sensor, also known as PT100.

r = 100 ( 1+000392T） - - - - - > R - 100=0392T- - - - - - - - - - > T = ( R - 100). 0392

- - - - - > T = 2551 ( R - 100).

PT100 dividing value: platinum thermal resistance is to use the platinum resistance changes with the temperature change of the basic principle of design and manufacture, at 0 ℃ resistance R ( ℃) The size of the divided into 10 ohm ( Index number for Pt10) And 100 ohm ( Index number of Pt100) Such as, temperature measuring range are - 200 ~ 850 ℃ for 10 ohm platinum thermal resistance of heat is original with coarser platinum wire winding and become, heat-resistant properties are better than those of platinum thermal resistance of 100 ohms, as long as used in the temperature range of above 650 ℃; 100 ohm platinum thermal resistance is mainly used for temperature below 650 ℃, although also can be used in the temperature range of 650 ℃ above, but in the temperature range of 650 ℃ above are not allowed to have A level of error. 100 ohm platinum thermal resistance of the resolution of the resolution of the platinum thermal resistance than 10 ohms 10 times larger, accordingly to the requirement of secondary instrument an order of magnitude, so in the temperature range of 650 ℃ below temperature should try to choose 100 ohm platinum thermal resistance.

thermal element skeleton material also is the main factor of decided to use the platinic resistance temperature area, common thermal element are ceramic element, glass components, mica elements, they are made of platinum wire around the ceramic skeleton respectively, glass frame, again on mica skeleton through a complicated process. Due to the performance of the different skeleton material itself, ceramic element is suitable for the temperature range of 850 ℃ below, glass components is suitable for the temperature range of 550 ℃ below. Appeared on the market in recent years, a lot of thick film and thin film platinum thermal resistance temperature sensing element, thick film platinum thermal resistance element is to use platinum paste printing on the glass or ceramic plate, thin film platinum thermal resistance element is used platinum paste splash in glass or ceramic floor, then through photolithography, the temperature sensing element applies only to - Temperature range of 70 ~ 500 ℃, but the temperature sensing element material, can be mass production mechanization, high efficiency, cheap price.

PT100 structure: in terms of structure, and the platinum resistance can also be divided into industrial platinum thermal resistance and armoured platinum thermal resistance. Industrial platinum resistance is also called assembly platinum thermal resistance, that is, platinum thermal resistance sensor components will be welded on the wire assembly in metal or ceramic tube closed at one end, and then install on the junction box; Armoured platinum thermal resistance is the platinum thermal resistance element, transition, lead insulation powder in stainless steel tube to mold assembly pull firm as a whole, has a solid, anti-seismic, can be round, wire diameter is small, the advantages of easy installation.

2, PT100 and connection of PLC analog input module

can have three ways to wiring resistance thermometer:

• 4 wire connection

3 wire connection,

• 2 wire connection

for 4 wire connection and 3 wire connection, through the terminal Ic + and Ic - module Provide constant current, so can compensate when measuring circuit of voltage dip. At this time must be constant current cable directly connected to a resistance thermometer. Compared with the 2 wire measurement, use wire 3 or 4 wire component compensation measure the returned result is more accurate.

4 wire connection resistance thermometer: in M + and M - The joint, can measure the voltage resistance thermometer. To connect, please observe the Ic + M + and Ic M - The polarity of the connections, and to ensure that these lines are connected directly with resistance thermometer.

3 wire connection resistance thermometer: for 3 wire connection, must in the M - usually And Ic - Put a connection between the plug. When connected, ensure that the connection circuit Ic + and M + connected directly to the resistance thermometer.

2 wire connection resistance thermometer: for a 2 wire connection, must be on the connector terminal M + in front of the module and Ic + insert a connection between the plug, in terminal M - And Ic - Insert another connection between plug.