The calibration bath is liquid, molten salt or molten pure metal as the medium, through the action of temperature control system and stirring or spraying device. Reach the set temperature and maintain uniform temperature in its inner working area. It is mainly used to detect and calibrate the constant temperature equipment required for various thermometers or other measuring instruments.
Commonly used media for calibration baths are water, silicone oil, antifreeze, absolute ethanol, tin, salt, etc., which respectively constitute alcohol low-temperature calibration baths, water baths, oil baths, high-temperature tin baths, and high-temperature salt baths.

The medium used in the liquid calibration bath of general temperature is generally water or silicone oil, and the temperature range is 70℃ ~300℃.
The introduction of the use of low temperature night body bath is generally antifreeze and absolute ethanol, and the calibration temperature range is -100℃ ~100℃.
The medium used in the high-temperature liquid calibration bath is generally a special medium such as tin and salt, and the calibration temperature range can reach up to 500℃ or even higher.
The special special medium used in the ultra-low temperature liquid calibration bath, the calibration temperature range can be as low as -180℃, or even lower.
The liquid calibration bath using silicone oil as the medium will volatilize and emit smoke when it is heated, which will not only pollute the environment, but also affect the health of the staff. Some liquid calibration baths have an active smoke exhaust function (such as the DTS-CT Intelligent calibration bath series), which can avoid the above-mentioned pollution. They are environmentally friendly products and have broad market prospects.

 

1. What Is a Temperature Bath For Calibration?

A temperature calibration bath is a piece of equipment used to calibrate thermometers and other temperature-measuring instruments. It consists of a container filled with a liquid or solid that can be heated or cooled to a precise temperature. The instrument to be calibrated is placed in the bath and its reading is compared to the known temperature of the bath.

 

2. Application Of Calibration Baths

Calibration baths, as you learned, are crucial tools for ensuring the accuracy of temperature measurements across various industries. Their applications extend far beyond simply verifying thermometer readings. Here are some of the key areas where calibration baths play a vital role:

1. Manufacturing:

Quality control: In manufacturing processes involving precise temperature control, like plastic injection molding or metalworking, calibration baths ensure the accuracy of temperature sensors used in equipment. This helps maintain consistent product quality and prevents defects.

Calibration of measuring instruments: Various temperature gauges, probes, and data loggers used in manufacturing are regularly calibrated using baths to ensure their readings align with established standards.

2. Food and beverage processing:

Food safety: Maintaining proper temperatures during food processing is critical for preventing bacterial growth and ensuring product safety. Calibration baths help verify the accuracy of thermometers used in cooking, chilling, and storage, promoting food safety compliance.

Product quality control: Consistent temperature control is essential for optimal flavor, texture, and shelf life of food and beverages. Calibration baths help ensure accurate readings from temperature sensors used in ovens, freezers, and other processing equipment.

3. Pharmaceutical industry:

Drug manufacturing and testing: Precise temperature control is vital in various stages of drug development and production. Calibration baths ensure the accuracy of sensors used in reactors, freezers, and incubators, guaranteeing drug quality and efficacy.

Vaccine storage and transportation: Maintaining proper storage and transportation temperatures for vaccines is critical for their effectiveness. Calibration baths are used to verify the accuracy of temperature sensors in refrigerators and transport containers, ensuring vaccine potency.

4. Chemical industry:

Chemical reactions and processes: Many chemical reactions require precise temperature control for optimal yield and safety. Calibration baths ensure the accuracy of sensors used in reactors, distillation columns, and other equipment, optimizing chemical processes.

Material testing: The properties of many materials, like polymers and adhesives, are highly temperature-dependent. Calibration baths are used to verify the accuracy of sensors used in material testing equipment, ensuring reliable data for research and development.

5. Aerospace industry:

Aircraft engine testing: Aircraft engines operate at extreme temperatures. Calibration baths are used to verify the accuracy of sensors monitoring engine temperatures during testing, ensuring safe and efficient operation.

Satellite component testing: Satellites operate in harsh environments with extreme temperature fluctuations. Calibration baths are used to test the thermal tolerance of satellite components, guaranteeing their functionality in space.

These are just a few examples of the diverse applications of calibration baths. Their accuracy and reliability make them indispensable tools for maintaining temperature control standards across various industries, ensuring product quality, safety, and process efficiency.

 

3. Common Types Of Calibration Baths

When it comes to calibrating your temperature-sensitive instruments, the type of bath you choose matters. Here's a breakdown of the most common calibration bath types, each with its own strengths and applications:

1. Liquid Baths:

The classics: Liquid baths use a heated or cooled liquid (water, oil, glycol) as the heat transfer medium. They're versatile and widely used for calibrating thermometers, probes, and other instruments designed for liquid environments.

Benefits: Excellent temperature uniformity, good heat transfer, suitable for large instruments.

Drawbacks: Can be messy with spills, limited temperature range for certain liquids, slower temperature changes compared to dry baths.

2. Dry Baths:

Solid performers: Dry baths use a solid block (aluminum, sand) heated or cooled to provide a dry, stable temperature environment. They're ideal for calibrating thermometers and probes used in air or gas applications.

Benefits: Fast temperature changes, clean and mess-free, wider temperature range than some liquids, good portability.

Drawbacks: Limited well size for larger instruments, slightly less temperature uniformity compared to liquid baths, potential for thermal gradients within the block.

3. Micro-Baths:

Small but mighty: Micro-baths are compact liquid baths designed for calibrating small sensors and probes with limited immersion depth. They're perfect for space-constrained applications or calibrating multiple instruments simultaneously.

Benefits: Small footprint, ideal for tiny sensors, multiple well options for batch calibration, good temperature stability.

Drawbacks: Limited volume restricts immersion depth, not suitable for larger instruments, slower temperature changes compared to larger baths.

4. High-Temperature Baths:

Going hot: High-temperature baths specialize in reaching and maintaining exceptionally high temperatures, often exceeding 300°C. They're crucial for calibrating instruments used in molten metals, furnaces, and other high-heat environments.

Benefits: Exceptional temperature range, suitable for specialized applications, robust construction for harsh environments.

Drawbacks: Higher cost, specialized safety considerations, limited liquid choices due to high temperatures.

5. Custom Baths:

Tailored solutions: For unique needs, custom baths can be designed with specific features like deep wells, multiple compartments, or integrated stirring mechanisms. They offer ultimate flexibility for highly specialized applications.

Benefits: Precisely meet unique requirements, optimize immersion depth and instrument compatibility, enhance workflow efficiency.

Drawbacks: Higher cost and lead time compared to standard baths, less readily available, require detailed specifications.

 

4. How Do You Calibrate An Rtd?

Calibrating an RTD (Resistance Temperature Detector) involves comparing its resistance values at specific temperatures to known, accurate reference values. Here's a general outline of the process:

 

Preparation:

Gather equipment: You'll need a precision temperature bath, a reference thermometer with traceable calibration, appropriate connectors for your RTD, and a multimeter or dedicated RTD reader.

Connect the RTD: Follow the manufacturer's instructions for your specific RTD and connection type (2-wire, 3-wire, or 4-wire). Ensure tight connections to minimize resistance errors.

Prepare the bath: Fill the temperature bath with the appropriate liquid for your desired temperature range and preheat/cool it to the first calibration point.

 

Calibration Process:

Immerse the RTD: Carefully place the RTD and reference thermometer in the bath, ensuring they're not touching each other or the bath walls. Allow sufficient time for thermal equilibrium (usually 5-10 minutes).

Measure resistance: Using your multimeter or reader, measure the RTD's resistance at the stabilized temperature. Record the value along with the reference thermometer's reading and bath temperature.

Repeat at different temperatures: Perform the measurement and recording steps at several points across your desired temperature range, following the calibration procedure recommended by the RTD manufacturer. Some baths allow automatic stepping through multiple calibration points.

Analyze and adjust: Compare the measured RTD resistances to the known reference values at each temperature point. Calculate the deviation (error) and analyze the trend throughout the range. If necessary, adjust the RTD's internal calibration resistor according to the manufacturer's instructions to reduce the error.

 

5. Why Do We Use Kerosene In Low Temperature Calibration Bath?

While kerosene was once commonly used in low-temperature calibration baths, its use has largely been replaced by other fluids due to safety concerns and environmental considerations. However, it's still helpful to understand why kerosene was initially preferred and what its limitations are.

 

Why kerosene was used:

Wide liquid range: Kerosene remains liquid across a relatively wide temperature range, from around -40°C to 250°C. This allowed for a single fluid to be used for calibrating instruments across a broad spectrum of low temperatures.

Good heat transfer: Kerosene has decent thermal conductivity, meaning it efficiently transfers heat to the instruments being calibrated, ensuring accurate and consistent temperature readings.

Readily available: Kerosene was historically a readily available and relatively inexpensive fluid, making it a practical choice for calibration baths.

 

Limitations of kerosene:

Safety hazards: Kerosene is a flammable liquid with a flash point around 38°C. This poses a significant fire risk, especially in enclosed laboratory settings.

Environmental concerns: Kerosene is a petroleum-based product, and its use and disposal raise environmental concerns. Spills can contaminate soil and water, and improper disposal can contribute to air pollution.

Health risks: Kerosene vapors can be harmful if inhaled, and prolonged exposure can irritate the skin and eyes.

 

Modern alternatives:

Silicone oils: These synthetic oils offer a wider temperature range than kerosene, typically from -70°C to 200°C, while being non-flammable and much less harmful to the environment.

Glycols: Certain glycol-based fluids, like ethylene glycol, are also suitable for low-temperature calibration baths, with good thermal properties and non-flammability.

Alcohol mixtures: For even lower temperatures, mixtures of alcohols like ethanol and methanol can be used, reaching down to -90°C. However, they require special precautions due to their high flammability.

 

6. High Temperature Calibration Bath Vs Low Temperature Calibration Bath

Feature	High-Temperature Baths	Low-Temperature Baths
Temperature Range	Typically above 300°C	Typically from -80°C to 200°C
Fluid Choices	Molten salts, molten metals, high-temperature oils	Silicone oils, ethylene glycol, alcohol mixtures
Construction Materials	Stainless steel, ceramics, refractory materials	Stainless steel, aluminum, plastic
Applications	Aerospace, metallurgy, chemical processing, energy production	Pharmaceutical research, cryogenic testing, food processing, environmental monitoring
Safety Considerations	Strict	Lower
Selection	Consider temperature range, instrument compatibility, safety requirements, budget, environmental impact	Consider temperature range, instrument compatibility, safety requirements, budget, environmental impact