RTD temperature measurement principle and materials

Resistance temperature measurement is based on the fact that the resistance of a metal  conductor increases with temperature. RTDs are mostly made of pure metals, with  platinum and copper being the most widely used, but they are now being made from  materials  such as nickel, manganese, and rhodium.

The end- face RTD temperature sensing element is wound with specially treated resistancewires.

How the resistance value changes

The end- face RTD is a temperature sensor that converts the temperature into a resistive  quantity by using the principle that its resistance value changes with the change of  temperature. Temperature measuring equipment such as temperature transmitters,  temperature control meters, and PLC templates obtain resistance values by applying a  known excitation current to the end surface thermal resistance to measure the voltage at both ends, and then convert the resistance value into a temperature value, so as to  realize temperature measurement. Temperature measuring devices generally have four  input terminals. Among them, I and I- provide constant current to the end-face RTD, and V and V- are used to detect the voltage change of the end-face RTD, and detect the temperature change accordingly.

The end face thermal resistance is used for industrial water, domestic water, sewage and  other weakly corrosive media, suitable for petroleum, chemical, steel and other industrial  sectors, municipal, environmental protection and other fields. Alloy B protection tube: It  has good corrosion resistance to all concentrations of hydrochloric acid below the boiling point, and is also resistant to the corrosion of non-chlorinated acids, alkalis and non-oxidizing salts such as sulfuric acid, phosphoric acid, hydrofluoric acid, organic acid, etc.  Alloy C protection tube: It can resist the corrosion of non-oxidizing acids, such as nitric acid, mixed acid, or mixed medium of chromic acid and  sulfuric acid, and also resist the corrosion of oxidizing salts Fe, Cu or other oxidizing  agents, such as hypochlorite solution and seawater corrosion higher than room  temperature. Titanium protection tube: can resist the corrosion of seawater, various  chlorides and hypochlorite, oxidizing acids, organic acids and alkalis. It is not resistant to  corrosion by purer reducing acids, but if the acid contains an oxidizing agent, the  corrosion is greatly reduced.

PTFE protective tube: It is a plastic with the most stable chemical properties, which can  resist boiling hydrochloric acid, sulfuric acid, nitric acid and aqua regia, as well as  concentrated alkali and various organic solvents. It is not resistant to chlorine trifluoride,  high  temperature chlorine trifluoride, high-speed liquid fluorine, liquid oxygen, and ozone.

Precautions for use

1. The temperature measurement system is generally composed of thermal resistance, connecting wires and display instruments. The following two points must be noted: the index number of the RTD and the display instrument must be consistent; In order to eliminate the effect of changes in the resistance of the connecting wires, a three-wire connection method must be used.

2. The end face thermal resistance is a solid body composed of temperature sensing elements (resistive bodies), leads, insulating materials, and stainless steel sleeves, and its  outer diameter is generally φ1~φ8mm. Compared with ordinary RTD, the end RTD has the following advantages: small size, no air gap inside, small measurement hysteresis in thermal inertia; Good mechanical properties, vibration resistance, impact resistance; It can be  bent, easy to install, and has a long service life.

3.The end- face RTD temperature sensing element is wound by specially treated resistance wire and is tightly attached to the end face of the thermometer. Compared with general  axial RTD, it can reflect the actual temperature of the measured end face more accurately  and quickly, and is suitable for measuring the end face temperature of bearings and other parts.

4. Flameproof thermal resistance flameproof thermal resistance through a special structureof the junction box, the shell of the explosive gas mixture due to sparks or arc and other  influences of the resistance body to repair the circuit must change the length of the  resistance wire and affect the resistance value, for this to replace the new resistor body as well, if the use of welding repair, after welding to pass the calibration before use.