- What is a Temperature Gauge?
- Temperature gauge working principle
- Various types of Temperature Gauges used in Industries
- Bimetal Dial Thermometer Temperature Gauge
- How does a bimetal temperature gauge work?
- Gas Filled Dial Thermometer Temperature Gauge
- Liquid-Filled Dial Thermometer Temperature Gauge
- Indicating Temperature Switch
- Digital Display Thermometer / Indicator
- What is the best temperature gauge?
- When is an expansion temperature gauge suitable?
- How does a temperature gauge using the gas-actuation principle work?
- When is a machine-glass temperature gauge used?
What is a Temperature Gauge?
Temperature gauges assess the thermal state of a homogeneous substance. For accurate measurement, the measuring system should be closely aligned with the body being measured. The most common methods for temperature measurement are based on the temperature-dependent properties of the substance or body.
- It is a field-mounted temperature sensor.
- It measures the present temperature of the body.
- The temperature gauge is a dial-type temperature-indicating device.
- The gauge is used only for display purposes, but this is not used to control the temperature of the body.
- Temperature gauges are available in various dial sizes, various ranges, and in different scales such as Degrees-Celsius and Degrees Fahrenheit scales.
- Most of the process industries use gauges having a Degree Celsius scale.
Temperature gauge working principle
The working principle of a temperature gauge depends on its type, but the general concept involves detecting temperature changes and converting them into a readable display.
Mechanical Temperature Gauges:
Bimetallic Strip Gauges:
- Principle: These gauges use a bimetallic strip made of two different metals with distinct coefficients of thermal expansion. When the temperature changes, the strip bends due to the differential expansion of the metals.
- Operation: The bending motion is transmitted to a pointer, which moves across a calibrated scale to indicate the temperature.
Expansion Thermometer Gauges:
- Principle: These gauges consist of a bulb filled with a liquid, vapor, or gas connected to a Bourdon tube through a capillary. The fluid inside expands or contracts with temperature changes.
- Operation: The change in fluid volume causes a pressure change within the Bourdon tube, which then deforms and moves the pointer on the display.
Gas-Actuated Gauges:
- Principle: These use an inert gas contained in a sealed system that includes a bulb, capillary tube, and Bourdon tube. The gas pressure changes with temperature variations.
- Operation: The pressure change deforms the Bourdon tube, which drives a pointer across a scale to indicate the temperature. A bimetal element may be used for temperature compensation.
Digital Temperature Gauges:
Thermocouple Gauges:
- Principle: Thermocouples generate a small voltage proportional to the temperature difference between two dissimilar metal junctions.
- Operation: This voltage is processed by a microcontroller to display the temperature digitally.
Resistance Temperature Detectors (RTDs):
- Principle: RTDs operate on the principle that the electrical resistance of a metal changes with temperature.
- Operation: The resistance is measured and converted into a temperature reading by the gauge’s digital circuitry.
Thermistors:
- Principle: Thermistors are temperature-sensitive resistors whose resistance changes significantly with temperature.
- Operation: The gauge measures this resistance change and converts it into a temperature value for display.
Various types of Temperature Gauges used in Industries
A temperature gauge is a device, either mechanical or digital, used to measure and display the temperature of fluids or gases in pipelines, tanks, or vessels. It operates with a sensing element, like a bulb or thermocouple, which detects temperature changes and relays this information to a display unit. Temperature gauges vary in type, size, accuracy, and temperature range, with some designed for low temperatures and others for high-temperature environments, such as furnaces or boilers. They can also be tailored for specific fluids or gases, particularly in industries like chemical processing.
Temperature gauges are extensively used across various industries, including oil and gas, chemical processing, food and beverage, pharmaceuticals, and HVAC (heating, ventilation, and air conditioning). Often, they are paired with other instruments, such as temperature transmitters, to form a comprehensive measurement and control system for industrial processes.
Bimetal Dial Thermometer Temperature Gauge
Features of Bimetal Dial Thermometer Temperature Gauge:
- The bimetal Dial thermometer consists of a bimetal strip in the form of a helix
- It works on the principle of thermal expansion: when two metals with different coefficients of expansions are joined to form a bimetal. The expansion of bimetal is proportional to changes in temperature.
- Bimetal dial thermometers are simple in construction.
- Rugged construction with Protection class IP-67
- Suitable for most industrial process applications
- The temperature range varies from – 50 to 600 Degrees Celsius.
- It has a rigid stem with a fast Response is fast.
- Hermetically sealed case.
- It is available with bottom entry, back entry, and every angle rotatable construction.
- Accuracy ± 1%Full Scale Deflection.
- Repeatability is high and has minimum hysteresis.
Specifications of Bimetal Dial Thermometer Temperature Gauge:
| Reference Standard | ASMEB 40.200, EN 13190 |
| Dial | 100 mm or 150 mm aluminium white background with black markings. |
| Case | Stainless Steel-304 or 316 with bayonet bezel. |
| Protection | Weatherproof IP – 67 class (IS/IEC : 60947 / IEC : 60529) |
| Window | Shatter proof glass |
| Pointer | Aluminium, black, micrometre adjustable |
| Stem | SS304 or SS316 in 6 mm, 8 mm, 10 mm, and 12 mm diameter, and length varies from 100 mm to 1000 mm. |
| Connection | Standard Half-inch NPT connection |
| Range | 50Degree C to 600 Degree C with a minimum span of 60 Degree C. |
| Accuracy | ± 1% Full Scale Deflection |
| Over range | 125% Full Scale Deflection up to max temperature range of 500°C |
| Reset | Micrometer Pointer (standard), External (optional) |
| Optional | 1) Silicon Oil Filled Case Suitable up to 339°C Max 2) Contacts: 1 SPST, N-O to close on the rise of drop in temperature (specify action required) adjustablefor full range, with a current rating of 30 VA @ 230 V AC, only for 100 mm dial, back entry. |
Ordering Information MODEL: BDT
How does a bimetal temperature gauge work?
A bimetal temperature gauge operates using a measuring system in the form of a helical or spiral tube. This system consists of two metal strips with different expansion coefficients, bonded together. When the temperature changes, the differing expansion rates of the two metals cause the bimetal strip to deform, creating a rotational movement. With one end of the bimetal strip fixed, this movement rotates the pointer shaft, indicating the temperature. These gauges can measure temperatures ranging from -70 to +600 °C (-94 to +1,112 °F) and are available in accuracy classes 1 and 2, according to EN 13190.
Gas Filled Dial Thermometer Temperature Gauge
Features of Gas Filled Dial Thermometer Temperature Gauge:
- Gas-filled dial thermometer temperature gauges defeat the limitations of other temperature gauges
- It operates over a wide temperature range of about – 200 to 800 Degrees Celsius
- The stem is offered without accuracy loss.
- The capillary length of this dial-type gauge is up to 25m
- Inert (N2) gas is nonhazardous, and the nontoxic nature of the filled systems makes it an ideal choice for a cross-section of industries.
- Suitable for sanitary application
- All SS construction
- Rigid stem or capillary type
- Fast response
- High reliability and accuracy ± 1% FSD
- IP-67 protection
Specifications of Gas Filled Dial Thermometer Temperature Gauge:
| Reference Standard | ASMEB 40.200, EN 13190 |
| System | Nitrogen Gas filled compensated in accordance with SAMA CI. Ill B |
| Dial | 100 mm or 150 mm aluminium white background with black markings. |
| Case | Stainless Steel-304 or 316 with bayonet bezel. |
| Protection | Weatherproof IP – 67 class (IS/IEC : 60947 / IEC : 60529) |
| Window | Shatter proof glass |
| Pointer | Aluminium, black, micrometre adjustable |
| Stem | Stainless Steel- 304 or 316 in 6 mm, 8 mm, 10 mm, and 12 mm diameter as standard Connection |
| Connection | 11/2 inch NPT adjustable. |
| Range | (-) 200°C to 800°C with a minimum span of 80°C |
| Accuracy | ± 1% FSD |
| Over range | 125% Full Scale Deflection up to max temperature range of 500°C |
| Reset | Micrometer Pointer (standard) |
| Optional | Silicon Oil Filled Case Suitable for about 339°C |
Ordering Information: GDT-R / GDT-C
GDT-R – Rigid Stem
GDT-C – Capillary Type
Liquid-Filled Dial Thermometer Temperature Gauge
Features of Liquid-Filled Dial Thermometer Temperature Gauge:
- Temperature measurement is based on the principle of liquid-filled expansion
- Temperature range (-) 30°C to 250°C
- Replaces mercury-type thermometers.
- Used in various industries such as food processing, pharmaceutical, and biotechnology.
- The main advantage is the minimum immersion length required for sensing (30mm) which makes it suitable for lower line sizes
- Rugged construction.
- Accuracy ± 1% FSD
Specifications of Liquid-Filled Dial Thermometer Temperature Gauge:
| Reference Standard | ASMEB 40.200, EN 13190 |
| System | Liquid-filled type compensated in accordance with SAMA CI. I-B |
| Dial | 100 mm or 150 mm aluminium white background with black markings. |
| Case | Stainless Steel-304 or 316 with bayonet bezel. |
| Protection | Weatherproof IP – 67 class (IS/IEC : 60947 / IEC : 60529) |
| Window | Shatter proof glass |
| Pointer | Aluminium, black, micrometre adjustable |
| Stem | Stainless Steel- 304 or 316 in 6 mm, 8 mm, 10 mm, and 12 mm diameter as standard material. (possible immersion length must be about 30 mm) |
| Capillary | SS Covered/SS Covered + PVC/SS Covered + SS armored/SS Covered + SS Armoured +PVC (up to 5 Mtr.). |
| Connection | 1/2 inch NPTas standard with adjustable compression fitting. |
| Range | (-) 30°C to 500°C with a minimum span of 50°C |
| Accuracy | ± 1% FSD |
| Over range | 125% FSD (up to max temp range of 500°C ) |
| Reset | Micrometer Pointer |
| Optional | Silicon Oil Filled Case |
Ordering Information LDT-R / LDT-C:
LDT-R – Rigid Stem
LDT-C – Capillary Type
Indicating Temperature Switch
Features of Indicating Temperature Switch:
- Combines indication with switching in order to make or break the associated electrical circuit
- Can be offered with contact assembly as well as micro switch (as a combination of switch and movement)
- Fast response
- Switching accuracy ± 2% FSD
- High repeatability and low hysteresis
- Flameproof version available
- Case compensated system
Specifications of Indicating Temperature Switch:
| Reference | Nitrogen gas filled type compensated in accordance with SAMA CI. III-B |
| Dial | 100 mm or 150 mm aluminium white background with black markings. |
| Case | Stainless Steel-304 or 316 with bayonet bezel. |
| Protection | Waterproof to IP – 67 (IS/IEC: 60947 / IEC: 60529) Flameproof to IIA MB (Equivalent to NEC CI. I Div 2 Gr. C&D) Flameproof to IIC (Equivalent to NEC CI. Div 1 Gr. A&B) |
| Stem | Stainless Steel-304/316 in 6 mm, 8 mm, 10 mm, 12 mm diameter as standard material. |
| Capillary | SS Covered/SS Covered + PVC/SS Covered + SS armoured/SS Covered + SS Armoured +PVC (up to 25 Mtr.). |
| Connection | ½ inch NPT compression fitting as the standard connection. |
| Range | (-) 200°C to 800°C with a minimum span of 80°C |
| Accuracy | ± 1% FSD for indication, ± 2% FSD for switching. |
| Over range | 125% FSD |
| Contacts | 1) SPST, single, normally open, closes on rising in temperature or vice versa, rated 30 VA @ 230V AC |
| Accessory | Relay for the contact assembly to match the current of 5 amp @ 230 V AC separate mounted. |
| Note | a. Flameproof version is offered with Single Pole Double Throughput Micro switch in Die-Cast only in Aluminium housing. b. For minimum insertion length essential for propersensing, contact our design department. c. Three-point calibration certificate accompanies each thermometer. d. For operating temp>600°C; the stem of SS310 / Inconel 600 shall be recommended. |
Ordering Information MODEL : GDT-SW-R / GDT-SW-C
GDT-SW-R – Rigid Stem
GDT-SW-C – Capillary Type
Digital Display Thermometer / Indicator
The Digital / Wireless Thermometer range is replaced by digital temperature gauges. These digital gauges are contemporary more superior in technology.
Features of Digital Display Thermometer / Indicator:
- Universal RTD or Thermocouple input.
- BATTERY Powered.
- USB & NFC Interface for easy data transfer.
- Alarm or Relay configured to indicate lower battery status .
- User set display messaging.
- 5000 Point data logging along with Real-time clock.
- This is not only a temperature-displaying unit.
- It functions as a data logger to download the information by using an android application.
- It displays information such as over temperature and low battery.
DM-650TMSCH4: Digital Display with IP67 Plastic Housing:
- This consists of a battery-powered indicator 6-digit LCD to display sensor temperature in Degrees Celsius and in Degrees Fahrenheit scale.
- It allows the user to display up to two messages of up to 32 characters.
- the user has the option to set an alarm within a temperature range.
- The translation relay is used together with messaging and alerts to provide switching at user-set switch points.
- Data logger to store up to 5000 points.
- Feature highlights include relay trips, data logging functions, and battery-powered and real-time clocks.
DM-650 TMSS: Digital Display with Stainless Steel Housing:
- It consists of stainless steel housing, best suited for rough climatic conditions. It also includes a DUAL relay. The two transition relay is used together with messaging and alerts to provide switching at user-set switch points.
- Feature highlights include dual relays, a data logging function, battery-powered, real-time clock (great for stamping data logged points).
DM-650TMSSF: Digital Display with Stainless Steel body and panel for Wall Mounting:
This indicator features all of the above functions. The addition is a Stainless Steel mounting panel that can be used for an application requiring the indicator to be fixed on a wall or panel.
What is the best temperature gauge?
Temperature Gauge Selection
The “best” temperature gauge depends on the specific application and requirements, such as the temperature range, accuracy, environment, and the medium being measured. Here are some considerations for choosing the best temperature gauge for different situations and this table should help you select the best temperature gauge based on your specific needs and application
| Temperature Gauge Type | Best For | Advantages | Limitations |
| Bimetallic Temperature Gauge | General-purpose applications in HVAC, manufacturing, and light industrial settings. | Durable Simple to use No need for external power Suitable for a wide range of temperatures | Not suitable for highly precise measurements Limited for extreme temperatures |
| Gas-Actuated Temperature Gauge | High-accuracy applications in industrial settings (chemical processing, oil and gas, power generation). | High accuracy- Wide temperature range (-200 to +700 °C) Suitable for remote readings with capillary tubes | More complex Higher cost |
| Expansion Thermometer Gauge | Remote measurement locations and moderate accuracy applications. | Can measure from remote locations Good for moderate temperature range Available in various designs | Limited accuracy compared to digital gauges |
| Digital Temperature Gauge (Thermocouple, RTD, Thermistor) | Precision measurement, data logging, and integration with control systems in labs, process industries, and research. | High accuracy Digital readout Interfaces with computers/controllers Measures extreme temperatures depending on sensor type | Requires power supply Can be more expensive |
| Infrared (IR) Temperature Gauge | Non-contact measurement in hazardous, moving, or inaccessible environments. | Fast response No contact needed Suitable for high temperatures Safe for hazardous environments | Affected by surface emissivity and ambient conditions Less accurate than contact methods for precise measurements |
When is an expansion temperature gauge suitable?
An expansion temperature gauge, which includes a temperature probe, a capillary, and a Bourdon tube, is ideal for measuring temperatures at remote locations. The system is filled with liquid, and as the temperature changes, the internal pressure within the gauge also changes. This pressure is transmitted through a tube, moving the pointer shaft to display the temperature on a scale. By using remote capillaries ranging from 500 to 10,000 mm in length, these gauges can measure temperatures from distant locations. The measuring ranges for expansion temperature gauges span from -40 to +400 °C, with accuracy classes 1 and 2, according to EN 13190.
How does a temperature gauge using the gas-actuation principle work?
In a gas-actuated temperature gauge, the stem, capillary, and Bourdon tube are integrated into a single unit filled with inert gas. As the temperature fluctuates, the internal pressure changes, moving the pointer through the action of a measuring tube. To compensate for ambient temperature variations, a bimetal element is installed between the movement and the measuring tube. These gauges can measure temperatures with scale ranges from -200 to +700 °C (-328 to +1,292 °F) and are available in accuracy class 1.
When is a machine-glass temperature gauge used?
Machine-glass temperature gauges are used for monitoring temperatures in gases, vapors, and liquids within vessels and pipelines. The thermometer is encased, with a cutout for the scale display. These thermometers are commonly housed in a V-shaped case for easy visibility.
