The WSS Series Bimetallic Thermometer is an on-site instrument for measuring medium and low temperatures. It directly measures the temperature of liquids, steam, and gases from -80℃ to +500℃ in various production processes.

Working Principle

Bimetallic thermometers work by using two metals with different coefficients of thermal expansion. To improve temperature sensitivity, the metal strips are usually formed into a helical coil. When the temperature of the layered metals changes, their different degrees of expansion or contraction cause the coil to wind or unwind.

One end of the coil is fixed, while the other is connected to a freely rotating pointer. Thus, when the bimetallic strip senses a temperature change, the pointer indicates the temperature on a circular graduated scale.

The temperature measurement range of this instrument is -80℃ to +500℃, with a permissible error of approximately 1% of the scale span.

Classification and Selection Guidelines

1. Classification

Depending on the connection orientation between the dial and protective stem, bimetallic thermometers are divided into four types: axial, radial, 135° angle, and universal.

① Axial Bimetallic Thermometer: The dial is perpendicular to the protective stem.

② Radial Bimetallic Thermometer: The dial is parallel to the protective stem.

③ 135° Angle Bimetallic Thermometer: The dial and protective stem are connected at a 135° angle.

④ Universal Bimetallic Thermometer: The angle between the dial and protective stem can be adjusted freely.

Mounting Configurations

To meet different production requirements, bimetallic thermometers are available with various mounting arrangements: adjustable male threaded connection, adjustable female threaded connection, fixed threaded connection, compression fitting with threaded connection, compression fitting with flange, and fixed flange.

Model Designation

W S S □ □ □ □——Protection Type

None - Standard Type

Mounting Method W - Protective Type

0 - No Mounting Device F - Corrosion-Resistant Type

Structural Configuration 1 - Adjustable Male Thread

0 - Axial Type 2 - Adjustable Female Thread

1 - Radial Type 3 - Fixed Thread

2 - 135° Angle Type 4 - Fixed Thread

3 - Universal Type 5 - Compression Thread

Nominal Case Diameter 6 - Compression Flange

3-φ60

4-φ100

5-φ125

Bimetallic Temperature-Sensing Element

Metal Expansion Type

Temperature Instrument

Selection Guidelines

When selecting a bimetallic thermometer, fully consider the actual operating environment and requirements, including dial diameter, accuracy class, mounting method, measured medium, and environmental hazards. Cost-effectiveness and maintenance workload should also be considered.

During transportation, installation, and operation, avoid striking the temperature probe. To ensure measurement accuracy, the probe insertion depth into the medium should be at least 2/3 of the probe length. Do not twist the instrument housing during installation.

Applications:

WSS bimetallic thermometers equipped with thermocouples (or resistance temperature detectors) and temperature transmitters are temperature sensors that provide both local indication and remote electrical signal transmission. They can display temperature on site and transmit thermocouple (or RTD) signals or signals from two-wire temperature transmitters. These instruments are widely used in metallurgy, petrochemicals, electric power, light industry and textiles, food processing, national defense, and other industries. They integrate a thermocouple (or RTD), bimetallic thermometer, or temperature transmitter in one assembly. They are suitable for long-term operation in harsh environments, offering high accuracy and stable remote electrical signal transmission. A direct two-wire output is also available, improving interference resistance over long transmission distances.

Measurement Range Options: -20～+80,  -40～+80, 0～50, 0～100, 0～150, 0～200, 0～300, 0～400, 0～500, 0～600

Specifications:

WSS-301/WSS-311    Dial Diameter: 60MM    Thread Size: M16*1.5

WSS-401/WSS-411    Dial Diameter: 100MM    Thread Size: M27*2

WSS-501/WSS-511    Dial Diameter: 150MM     Thread Size: M27*2

Standard Stem Length: 100MM    (Customized longer lengths are available; an additional 100MM costs RMB 5.)

Indication Accuracy Class: 1.5

Introduction to Common Bimetallic Thermometer Types

1. Outdoor, Heavy-Duty Type

　　This bimetallic Thermometer is an on-site instrument suitable for measuring medium and low temperatures and can directly measure the temperature of liquids and gases.

　　Main Technical Specifications:

　　(1) Accuracy Class: 1.5

　　(2) Time Constant: J<40S

　　(3) Protective Stem Pressure Rating: 6.3MPa

　　(4) Contact Rating: 10VA rated power (non-inductive); maximum voltage: 220V AC; ****** operating current: 1A (non-inductive). Upper and lower limit contacts are normally open.

　　(5) Operating Ambient Temperature of Gauge Head: -25~55℃; 3. Specific models and related parameters.

2. Adjustable-Angle Type

　　The bimetallic thermometer is an on-site instrument suitable for medium and low temperature measurement and can directly measure the temperature of liquids and gases.

　　Main Technical Specifications

　　(1) Accuracy Class: 1.5

　　(2) Time Constant: J<40S

　　(3) Protective Stem Pressure Rating: 6.3MPa

　　(4) Contact Rating: 10VA rated power (non-inductive); maximum voltage: 220V AC; ****** operating current: 1A (non-inductive).

　　The upper and lower limit contacts are normally open.

　　(5) Operating Ambient Temperature of Gauge Head: -25~55℃

3. Vibration-Resistant Type

　　WSSXN Series Vibration-Resistant Electric Contact Bimetallic Thermometer is an on-site instrument for measuring medium and low temperatures. It can directly measure the temperature of liquids, steam, and gases in the -80℃ to +500℃ range during production processes, including in harsh, vibration-prone environments.

　　This vibration-resistant electric contact bimetallic thermometer is filled with vibration-damping oil to effectively reduce pointer fluctuations caused by mechanical vibration. Its design and construction offer water resistance, corrosion resistance, vibration resistance, clear indication, easy reading, mercury-free operation, and durability. It is widely used in petroleum, chemical processing, machinery, shipbuilding, power generation, textiles, dyeing and printing, and industrial and scientific research applications.

　　Main Features:

　　(1) On-site temperature display that is intuitive, convenient, safe, reliable, and offers a long service life;

　　(2) Various structural configurations to meet different requirements; mercury-free, easy to read, robust, and vibration-resistant;

　　(3) Protective stem materials include 1Gr18Ni9Ti stainless steel and molybdenum-titanium alloy, providing strong pressure and corrosion resistance;

(4) The removable-core thermometer allows quick maintenance or core replacement without stopping the equipment.

　　Working Principle:

　　The vibration-resistant electric contact bimetallic thermometer uses a coiled, curved bimetallic strip. As one end expands when heated, it rotates the pointer to indicate the corresponding temperature. To reduce environmental vibration, the bimetallic thermometer can be filled with silicone oil, or the display section of the bimetallic thermometer can be separated from the measuring section to achieve vibration resistance.

　　Vibration-resistant bimetallic thermometers are classified into integrated vibration-resistant electric contact bimetallic thermometers and separated vibration-resistant electric contact bimetallic thermometers.

　　Main Technical Specifications:

　　(1) Applicable Standards: JB/T8803-1998 GB3836-83

　　(2) Nominal Dial Diameter: 60 100 150

　　(3) Accuracy Class: (1.0), 1.5

　　(4) Thermal Response Time: ≤40S

　　(5) Protection Rating: IP55

　　(6) Angle Adjustment Error: Not greater than 1.0% of the measurement span

　　(7) Hysteresis: Not greater than the absolute value of the basic error limit

　　(8) Repeatability: Not greater than 1/2 of the absolute value of the basic error limit

4. Universal Type

　　This bimetallic thermometer is an on-site instrument suitable for medium and low temperature measurement and can directly measure the temperature of liquids and gases.

　　Main Technical Specifications:

　　(1) Nominal Dial Diameter: 100

　　(2) Accuracy Class: 1.0, 1.5

　　(3) Connection Size: M20x1.5, NPT1/2

　　(4) Thermal Response Time: ≤40s

　　(5) Protection Rating: IP55

5. Thermowell Type

　　The thermowell-type bimetallic thermometer can be used with various mounting thermowells to meet different pressure rating requirements. It can directly measure liquid, steam, and gas temperatures from -80℃ to +500℃ in production processes, as well as solid surface temperatures. It is widely used in petroleum, chemical processing, metallurgy, textiles, food processing, and other industries.

Installation Requirements

　　When installing a bimetallic thermometer, ensure measurement accuracy, safety, reliability, and ease of maintenance without affecting equipment operation or production. To meet these requirements, consider the following when choosing the mounting position and insertion depth of a resistance temperature detector:

　　(1) To ensure sufficient heat exchange between the sensing tip of the resistance temperature detector and the measured medium, select an appropriate measuring location. Avoid installing it near valves, elbows, and dead zones in piping or equipment.

(2) Resistance temperature detectors fitted with protective thermowells experience heat transfer and dissipation losses. To reduce measurement errors, thermocouples and resistance temperature detectors should have sufficient insertion depth:

　　a. When measuring the temperature of fluid at the center of a pipe, the sensing tip of the resistance temperature detector should generally reach the pipe center (vertical or inclined installation). For a pipe with a diameter of 200 mm, the recommended insertion depth is 100 mm;

　 　b. For temperature measurement of high-temperature, high-pressure, or high-velocity fluids (such as main steam), a shallow-insertion protective tube or thermowell-type resistance temperature detector can be used to reduce flow resistance and prevent tube breakage. For shallow-insertion RTD thermowells, the insertion depth into the main steam pipe should be at least 75 mm. The standard insertion depth for thermowell-type RTDs is 100 mm;

　　c. When measuring flue-gas temperature in a duct, an insertion depth of 1 m is sufficient even if the duct diameter is 4 m;

　　d. When the sensing element insertion depth exceeds 1 m, install it as vertically as possible or provide a support bracket and protective thermowell.

Operation and Maintenance

　　1. During storage, installation, operation, and transportation of WSS Series Bimetallic Thermometers, avoid impacts to the protective stem and do not allow it to bend or deform. Do not twist the instrument housing during installation.

　　2. The instrument should operate normally at an ambient temperature of -30℃ to 80℃.

　　3. The instrument should normally operate at a temperature between 1/2 and 3/4 of its scale range.

　 　4. Temperature Ranges of Bimetallic Thermometers: -80～+40℃ -40～+80℃ 0～50℃ 0～100℃ 0~120℃ 0～150℃ 0~160℃ 0～200℃ 0~250℃ 0～300℃ 0~350℃ 0～400℃ 0~450℃ 0～500℃ 0~550℃ 0~600℃

　　Measurement Ranges of Bimetallic Thermometers

Product Applications

Comparison of Bimetallic Thermometers with Similar Domestic Products:

① The instrument has an accuracy class of 1.0. Its upper housing is made of corrosion-resistant material, with a maximum temperature resistance of 200℃ and a minimum of -40℃.

② A flanged structure and double sealing rings provide good corrosion and water resistance.

③ The protective stem is welded using fully automatic argon shielding, producing strong welds with minimal intergranular corrosion.

④ The dial is printed on anodized aluminum, providing clear markings and an attractive appearance.

⑤ The pointer is internally adjustable.

In addition, the probe length of bimetallic thermometers can be customized to customer requirements. Their design and construction offer water resistance, corrosion resistance, flameproof protection, vibration resistance, clear indication, easy reading, mercury-free operation, and robust durability. They can replace other types of measuring instruments and are widely used in petroleum, chemical processing, machinery, shipbuilding, power generation, textiles, printing and dyeing, and industrial and scientific research applications.