Which is a good thermal resistor

Overview

It has many advantages, such as good disassembly of parts, easy maintenance, and low cost of replacing vulnerable parts

Prefabricated thermistor

Through remote transmission of electrical signals, it has high sensitivity, strong stability, good interchangeability, and accuracy. The room temperature insulation resistance of platinum resistance thermometers should not be less than 100M Ω, and the room temperature insulation resistance of copper resistance thermometers should not be less than 50M Ω. Widely used in production sites such as petroleum and chemical industries where various flammable and explosive gases and vapors are present.

The WZ series industrial thermistor is used as a temperature measurement sensor, usually paired with temperature transmitters, regulators, and display instruments to form a process control system. It is used to directly measure or control the temperature of liquid, steam, gas media, and solid surfaces within the range of -200 ℃ to 500 ℃ in various production processes.

Thermistor measures temperature by utilizing the characteristic that the resistance of a substance changes with temperature. When there is a temperature gradient in the measured medium, the measured temperature is the average temperature in the medium within the range of the temperature sensing element.

Although there are significant differences in the appearance of various thermal resistors, their basic structures are generally similar, consisting mainly of temperature sensing elements, insulation sleeves, protective tubes, and junction boxes.

working principle

Thermistor is a measurement method that utilizes the characteristic of a substance's resistance changing with temperature

Measuring temperature. When the resistance value changes, the working instrument displays the temperature value corresponding to the resistance value.

Prefabricated thermistorComposed of temperature sensing elements, external protective tubes, junction boxes, and various fixed devices for various purposes, there are two specifications of single and double support elements. The protective tube not only has anti-corrosion performance, but also has sufficient mechanical strength to ensure that the product can be safely used in various occasions. Temperature measurement principle: The resistance of a metal wire after being heated changes with temperature. The relationship between its thermal resistance value R (t) and the temperature t it is at can be expressed as R (t)=R0 (1+At+Bt2+...). The measured temperature value t can be obtained by checking the corresponding scale according to the measured resistance value.

Main technical parameters

Product execution standards

IEC584

IEC1515

GB/T16839-1997

JB/T5582-91

Room temperature insulation resistance

The thermal resistance is tested at an ambient temperature of 15-35 ° C, relative humidity not exceeding 80%, and a test voltage of 10-100V (DC). The insulation resistance between the electrode and the outer sleeve is greater than 100M Ω.

Measure temperature and tolerance

System Composition

(1) A thermistor temperature measurement system generally consists of a thermistor, connecting wires, and a display instrument. The following two points must be noted:

① The scale marks of the thermistor and display instrument must be *.

② In order to eliminate the influence of changes in the resistance of the connecting wires, a three wire connection method must be adopted. Please refer to Chapter 3 of this article for specific content.

(2) Armored thermal resistance is a solid body composed of temperature sensing elements (resistors), leads, insulation materials, and stainless steel sleeves. Its outer diameter is generally between 1 and 8mm, and can be as small as 2mm. Compared with ordinary thermistors, it has the following advantages:

① Small size, no air gap inside, low measurement lag in terms of thermal inertia.

② Good mechanical performance, vibration resistance, and impact resistance.

③ It can bend and is easy to install.

④ Long service life.

(3) The end face thermistor temperature sensing element is made of specially processed resistance wire wound tightly against the end face of the thermometer. Compared with general axial resistance thermometers, it can more accurately and quickly reflect the actual temperature of the measured end face, and is suitable for measuring the end face temperature of bearing shells and other components.

(4) The explosion-proof type thermal electric barrier type thermal resistor uses a special structure junction box to remove the explosive mixed gas inside its shell. If the resistor is damaged by sparks or arcs, the length of the resistance wire must be changed, which will affect the resistance value. Therefore, it is better to replace the resistor with a new one. If welding repair is used, it must be verified to be qualified after welding before use.

Instrument selection

Model, division number, temperature measurement range, ℃, temperature measurement points, protective tube material

WRN-230D K 0-1000 2-12 GH3030

0-800 1Cr18Ni9Ti

WRE-230D E 0-600 1Cr18Ni9Ti

WRN-430D K 0-1000 GH3030

0-800 1Cr18Ni9Ti

WRE-430D E 0-600 1Cr18Ni9Ti

1) Thermocouple Level I ordered according to the agreement;

2) Order the remaining materials of the protective tube according to the agreement;

3) External protection tube users should bring their own

Installation fixed form

fixed thread

Temperature measurement points M D H h SW d

2—6 M27x2 ￠40 ￠105 28 5 32 ￠20

7—12 M33x2 ￠48 ￠115 33 5 36 ￠34

Fixed Flange

Temperature measurement points D D1 D2 H do d

2—6 ￠105 ￠75 — 5 32 ￠20

7—12 ￠115 ￠85 — 5 36 ￠34

Selection Notice

1) Model number

2) Dividing number

3) Accuracy level

4) Number of thermocouple points

5) Installation fixed form

6) Material of protective tube

7) Length or insertion depth

Example: Multi point thermocouple, K-type, 3 points. L grade, fixed thread M27X2, L1=1200, L2=1500, L3=2000, WRN-220D3I grade L1=1200, L2=1500, L3=2000, thread M27x2

Technical index division number: Pt100, Cu50;

Measurement range: Pt100: -200~500 ℃;

Prefabricated thermistor

Cu50：-50～150℃；

Thermal response time: t0.5 ≤ 45s;

Allowable deviation: Pt100: *: ± (0.15+0.002 | t |);

B-level: ± (0.30+0.005 | t |);

Cu50：±（0.40+0.005|t|）；

Environmental temperature: -40 to+85 ℃;

Fixed flange or threaded type: -0.1~2.5MPa;

Active flange or threaded type: atmospheric pressure;

Electrical interface: M20 × 1.5;

Explosion proof mark: Explosion proof type: ExdIICT1-T6;

Intrinsic safety type: ExiaICT1~T6;

Protection level: IP65;

Insertion depth: 100-5000mm;

Diameter of protective tube: φ 12, φ 16, non standardized according to user requirements;

Material of protective tube: stainless steel, etc;

Thermal resistance insulation: The test voltage for insulation resistance at room temperature can be any value between 10-100V DC, and the ambient temperature should be within the range of 15-35 ℃, with a relative temperature not exceeding 80%. The insulation value at room temperature should be less than 100M Ω. Thermal resistors allow current to pass through platinum resistors, and the maximum measured current should not exceed 5mAPrefabricated thermistor

Process connection: Threaded connection: M16 × 1.5, M27 × 2;

Flange connection: HG20592-20635-97DN20 and above flanges, other flange standards (such as GB, JB/T, HGJ, ANSI, DIN, etc.), junction box material: aluminum alloy; stainless steel

feature

Good anti vibration performance;

High temperature measurement accuracy;

High mechanical strength;

Good pressure resistance performance;

Reliable and stable performance;

Good disassembly of parts;

Easy maintenance;

Low cost of replacing vulnerable parts;

Short thermal response time. Thermal response time: The time required for the output of a thermal resistor to change to 50% of the step change in temperature, represented by T0.5, is called the thermal response time.

Nominal pressure: generally refers to the static external pressure that the protective tube can withstand at room temperature without breaking, and the test pressure is generally 1.5 times the nominal pressure. In fact, the allowable nominal pressure is not only related to the material, diameter, and wall thickness of the protective tube, but also to its structural form, installation method, insertion depth, and the flow rate and type of the measured medium?

purpose

Usually used in conjunction with display, recording, and regulating instruments to directly measure various production processes ranging from -200 to 500

Liquids, vapors, and gases within the temperature range

Surface temperature of materials and solids. Provide accurate temperature change input signals for displays, recorders, regulators, scanners, data loggers, and computers.

material

difference

Thermocouples and thermal resistors both belong to contact temperature measurement in temperature measurement. Although they have the same function of measuring the temperature of objects, their principles and characteristics are not the same. Although thermal resistors are widely used in industry, due to theirthermocoupleThe temperature measurement range of thermal resistance limits its application to a certain extent. The temperature measurement principle of thermal resistance is based on the characteristic that the resistance value of a conductor or semiconductor changes with temperature. It also has many advantages, such as remote transmission of electrical signals, high sensitivity, strong stability, good interchangeability and accuracy. However, it requires power excitation and cannot measure temperature changes instantaneously. Industrial thermistors generally use Pt100, Pt10, Cu50, Cu100. The temperature measurement range of platinum thermistors is generally -200-800 degrees Celsius, while that of copper thermistors is -40 to 140 degrees Celsius. Thermistors and thermocouples have the same type of differentiation, but they do not require compensating wires and are cheaper than thermocouples.

Thermocouple is the most widely used temperature device in temperature measurement. Its main characteristics are wide measurement range, stable performance, simple structure, good dynamic response, and the ability to transmit 4-20mA electrical signals remotely, making it easy for automatic and centralized control. The temperature measurement principle of thermocouples is based on the thermoelectric effect. Connecting two different conductors or semiconductors into a closed circuit, when the temperatures at the two junctions are different, a thermoelectric potential will be generated in the circuit. This phenomenon is called thermoelectric effect, also known as Seebeck effect. The thermoelectric potential generated in a closed circuit consists of two types of potentials; Temperature difference potential and contact potential. Thermoelectric potential refers to the electric potential generated at the two ends of the same conductor due to different temperatures. Different conductors have different electron densities, so their electric potentials are also different. Contact potential, as the name suggests, refers to the electric potential generated when two different conductors come into contact because of their electron densitiesPrefabricated thermistor

The difference in electron diffusion results in the formation of an electric potential when they reach a certain equilibrium. The magnitude of the contact potential depends on the material properties of the two different conductors and the temperature at their contact point. At present, the thermocouples used in applications have a standard specification, which stipulates that thermocouples are divided into eight different divisions, namely B, R, S, K, N, E, J, and T. The lowest temperature they can measure is minus 270 degrees Celsius, and the highest can reach 1800 degrees Celsius. Among them, B, R, and S belong to the platinum series thermocouples. Since platinum is a precious metal, they are also called precious metal thermocouples, while the remaining ones are called cheap metal thermocouples. There are two types of thermocouple structures, ordinary type and armored type. Ordinary thermocouples are generally composed of hot electrodes, insulating tubes, protective sleeves, and junction boxes, while armored thermocouples are a solid combination of thermocouple wires, insulating materials, and metal protective sleeves assembled and stretched. However, the electrical signal of a thermocouple requires a special type of wire for transmission, which we call a compensating wire. Different thermocouples require different compensation wires, which are mainly used to connect with the thermocouple and keep the reference end of the thermocouple away from the power supply, thereby stabilizing the temperature of the reference end. Compensation wires are divided into two types: compensation type and extension type. The chemical composition of the extension wire is the same as that of the compensated thermocouple. However, in practice, the extension wire is not made of the same material as the thermocouple, and is generally replaced with a wire with the same electron density as the thermocouple. The connection between the compensating wire and the thermocouple is generally clear, with the positive pole of the thermocouple connected to the red wire of the compensating wire and the negative pole connected to the remaining color. The general compensation wire

Most of the materials are made of copper nickel alloy. Ordinary type thermistor

According to the temperature measurement principle of thermal resistance, the change in the measured temperature is directly measured through the change in the resistance value of the thermal resistance. Therefore, the change in resistance of various wires such as the lead wires of the thermal resistance body will have an impact on temperature measurement.

Armored thermistor is a solid body composed of temperature sensing elements (resistors), leads, insulation materials, and stainless steel sleeves. Its outer diameter is generally between 2 and 8mm, and can be as small as 2mm. Compared with ordinary thermistors, it has the following advantages: ① small size, no air gap inside, low measurement lag in terms of thermal inertia; ② Good mechanical performance, vibration resistance, and impact resistance; ③ Can bend, easy to install, and has a long service life. The end face thermistor temperature sensing element is made of specially processed resistance wire wound tightly against the end face of the thermometer. Compared with general axial resistance thermometers, it can more accurately and quickly reflect the actual temperature of the measured end face, and is suitable for measuring the end face temperature of bearing shells and other components.

Explosion proof thermistor uses a special structure of junction box to confine the explosion of explosive mixed gas inside its shell caused by sparks or arcs within the junction box, so as not to cause excessive explosion in the production site. Explosion proof thermal resistors can be used for temperature measurement in areas with explosive hazards within Bla-B3c class zones.