WR_K
JIECHUANG
Overview
Sheathed thermocouples offer numerous advantages such as flexibility, high pressure resistance, fast thermal response, and durability. Like industrial assembly thermocouples, they serve as temperature measurement sensors and are commonly used with display instruments, recording devices, and electronic controllers. They can also be used as the temperature-sensing elements for assembly thermocouples.
Sheathed thermocouples can directly measure temperatures ranging from 0°C to 800°C in various media, including liquids, steam, gases, and solid surfaces in various production processes. Additionally, they can be provided with outer protective tubes made of materials like Cr25Ni20, GH3030, GH3039, and 3YC-52, allowing temperature measurements up to 1200°C.
Temperature Measurement Range and Allowable Range | |||||||
Thermocouple Types | Code | Index | Proetective Tube OD (mm) | Common Temp (℃) | Max Temp (℃) | Allowable Deviation(△t) | |
Range (°C) | Permissible Error | ||||||
Platinum Rhodium10 — Platinum | WRPK | S | ≥∅3 | 1100 | 1200 | 0 ~ 1200 | ±1.5℃ or ±0.25%t |
Nickel-Chromim — Copper-Nickel | WREK | E | ≥∅3 | 600 | 700 | 0 ~ 700 | ±2.5℃ or ±0.75%t |
Nickel-Chromim — Nickel-Silicon | WRNK | K | ≥∅3 | 800 | 900 | 0 ~ 900 | ±2.5℃ or ±0.75%t |
Copper — Copper-Nickel | WRCK | T | ≥∅3 | 350 | 400 | -40 ~ ±350 | ±0.75%t |
Iron — Copper-Nickel | WRFK | J | ≥∅3 | 500 | 600 | 0 ~ 600 | ±2.5℃ or ±0.75%t |
note: t represents the absolute value of the measured temperature. | |||||||
l Thermal Response Time
The time required for the output of the thermocouple to reach 50% of a step change in temperature is known as the thermal response time, denoted as τ0.5(in seconds).
The thermal response time of sheathed thermocouples shall not exceed the specified values in the table below.
Thermal Response Time τ0.5 (s) | Sheathed | Insulated |
Protective Tube Diameter (mm) | ||
2.0 | 0.4 | 0.5 |
3.0 | 0.6 | 1.2 |
4.0 | 0.8 | 2.5 |
5.0 | 1.2 | 4.0 |
6.0 | 2.0 | 6.0 |
8.0 | 4.0 | 8.0 |
l Insulation Resistance
When the ambient air temperature is 20±15°C and the relative humidity is not greater than 80%, the insulation resistance between the thermocouple wires and the outer sheath of insulated Sheathed thermocouples shall comply with the specified values in the table below.
Protective Tube Diameter (mm) | Test Voltage (V-D.C) | Insulation Resistance (MΩ·m) |
0.5 ~ 1.5 | 50 ± 5 | ≥1000 |
> 1.5 | 500 ± 50 | ≥1000 |
l Standard Specifications for Outer Diameter and Nominal Length of Sheathed Thermocouples
Outer Diameter dmm | ||||
∅8 | ∅6 | ∅5 | ∅4 | ∅3 |
50 75 | 50 75 | 50 75 | 50 75 | 50 75 |
Note:
1. For insulated sheathed thermocouples with a diameter of ∅3 mm, the nominal total length L should not exceed 10000 mm.
2. For Sheathed thermocouples with a diameter d ≤ ∅5 mm and equipped with splash-proof or waterproof junction boxes, the exposed part of the thermocouple must be supported with additional brackets or other means during installation to increase rigidity, ensure fastening, and prevent swinging caused by vibration, thus avoiding damage to the thermocouple.
3. sheathed thermocouples with a diameter of ∅2 mm require consultation with our company for ordering.
Working Principle
The working principle of a Sheathed Thermocouple involves welding two conductors of different compositions at both ends to form a circuit. The end directly measuring temperature is called the measuring end, while the terminal end is called the reference end. When there is a temperature difference between the measuring end and the reference end, a thermoelectric current is generated in the circuit. When connected to a display instrument, the instrument indicates the corresponding temperature value of the thermoelectric potential generated by the Sheathed Thermocouple.
The thermoelectric potential of the Sheathed Thermocouple increases with the temperature at the measuring end. The magnitude of the thermoelectric potential depends only on the material of the Sheathed Thermocouple conductors and the temperature difference between the two ends, and is independent of the length and diameter of the thermoelectric elements.
The structure of a Sheathed Thermocouple consists of conductors, insulated magnesium oxide, and a protection tube made of 1Cr18Ni9Ti stainless steel, which is drawn multiple times. Sheathed Thermocouple products mainly consist of a junction box, terminal blocks, and the Sheathed Thermocouple itself, forming the basic structure, and are supplemented with various fixing devices.
l Material and Structural Composition of Sheathed Thermocouples
l Structural Forms of the Measuring End (Hot End)
l Installation of Fixed Types
The fixed devices are for user installation. Apart from products without fixed devices, sheathed thermocouple fixed devices come in four structural types: fixed compression fitting, adjustable compression fitting, fixed compression flange, and adjustable compression flange. The fixed compression fitting is for one-time user fixation, while the adjustable compression fitting allows for multiple fixations by the user.
l Compression Thread Fitting
Sheathed Thermocouple Outer Diameter d | ∅8 | ∅6 | ∅5 | ∅4 | ∅4 | ∅3 | ∅2 | |
Fixed Part Code & Dimensions | ||||||||
M | M16 × 1.5 | M12×1.5 | ||||||
S | 22 | 19 | ||||||
Sheathed Thermocouple Outer Diameter d | ∅8 | ∅6 | ∅5 | ∅4 | ∅4 | ∅3 | ∅2 | |
Fixed Part Code & Dimensions | ||||||||
D | ∅60 | ∅50 | ||||||
D0 | ∅42 | ∅36 | ||||||
D1 | ∅24 | ∅20 | ||||||
S | ∅22 | ∅19 | ||||||
d0 | ∅9 | ∅7 | ||||||
l Sheathed Thermocouple Free Junction (Terminal Box) Forms
The junction box is used to connect the free junction of the thermocouple to display instruments. Currently, there are various structural forms available, including simplified, splash-proof, waterproof, handheld, small junction box, plug-in, and compensating wire types.
Simplified type
Waterproof type
Handheld type
Small junction box type
