30+ Years of Precision Instruments
temperature controller is one of the most common temperature measurement components in industrial production. Its advantages are:
① high measurement accuracy. Because the platinum resistance thermometer is in direct contact with the object being measured, it is not affected by any intervening substances.
② Wide measurement coverage. Common platinum thermal resistance can be measured continuously from -45 to 2500 ℃, and some very platinum thermal resistance can be measured at least -229 ℃ (such as wrought iron nickel chromium alloy) and can reach 1300 ℃ (such as tungsten-rhenium). ③ Simple structure and convenient application. Generally speaking, platinum thermal resistance is composed of two different kinds of iron wires, and it will not be affected by the size and the initial tube bundle. There is a maintenance waterproof sleeve outside, which is extremely convenient to use.
1. Temperature Control Instruments Basic Concepts of Temperature Measurement
two different materials of electrical conductors or semiconductor materials A and B are welded together to form a closed loop.
when there is a temperature difference between the two stubborn points 1 and 2 of electrical conductors a and B, induced electromotive force is generated between each other, so in
a kind of current flow is formed in the control loop, which is called eddy current effect. Platinum resistance thermometers operate based on this effect.
2. temperature meter type and structure composition
(1) type of platinum thermal resistance
common platinum thermal resistance can be divided into standard platinum thermal resistance and non-standard platinum thermal resistance two categories. The enabled standard platinum thermal resistance refers to the platinum thermal resistance of our country's standard, which has the connection between its thermal potential difference and temperature, agrees to mistakes and leaks, and has a consistent standard measurement range table. It has the presentation surface of supporting facilities between the two to be used. Non-standard platinum thermal resistance is not as good as standard platinum thermal resistance in terms of application category or magnitude. Generally speaking, there is no consistent measurement range table. The key is to measure in some extraordinary places.
normative platinum thermal resistance in our country since January 1, 1994, platinum thermal resistance and thermocouple are all produced according to IEC international standards, and seven kinds of normative platinum thermal resistance s, B, e, k, r, j and t are specified as platinum thermal resistance of consistent overall planning in our country.
(2) the structure of the platinum thermal resistance is to ensure the firm and stable operation of the platinum thermal resistance. the following provisions are specified for its structure:
① the welding of the two thermoelectric stages forming the platinum thermal resistance must be firm;
② the two thermoelectric stages should be well insulated from each other to prevent short circuit faults;
③ the connection between platinum rhodium thermocouple and platinum thermal resistance should be convenient and firm.
④ the maintenance of waterproof casing should ensure sufficient isolation of thermoelectric grade and hazardous substances.
3. platinum thermal resistance cold end temperature compensation
because platinum thermal resistance materials are generally more precious (very when using precious metals), and the distance between the temperature measurement point and the surface is too far, so as to save platinum thermal resistance materials and control costs, generally speaking, platinum rhodium thermocouple is used to widen the cold end (self-made end) of platinum thermal resistance to a relatively stable temperature control room and connect it to the surface terminal. It must be emphasized that the actual effect of platinum thermal resistance platinum rhodium thermocouple only broadens the thermoelectric level and makes the cold end of platinum thermal resistance move to the surface terminal of the main control room. It cannot remove the harm of cold end temperature change to temperature measurement by itself and cannot compensate for the actual effect. Therefore, it is necessary to use other marking methods to compensate for the harm of temperature measurement when the cold end temperature t0 ≠ 0 ℃.
when applying platinum thermistor platinum rhodium thermocouple, attention must be paid to the type matching, the optical rotation cannot be inserted incorrectly, and the temperature at the butt end of platinum rhodium thermocouple and platinum thermistor cannot exceed 100 ℃. 
