Capillary thermostats are widely used in various applications, including heating, cooling, and temperature control systems. These devices rely on a sensing element consisting of a flexible capillary tube filled with a temperature-sensitive fluid, often a gas or liquid. Accurate calibration of capillary thermostats is crucial to ensure reliable and precise temperature control. One common method for calibration involves the use of salt and oil baths.

Benefits of Calibrating a Capillary Thermostat in a Salt or Oil BathCalibration Process of a Capillary Thermostat

  1. Stable and Uniform Temperature: Salt and oil baths provide a stable and uniform temperature environment, making them ideal for calibrating capillary thermostats. These baths exhibit excellent heat transfer properties, ensuring a consistent temperature throughout the calibration process. The use of a salt or oil bath minimizes temperature gradients, which can lead to inaccurate calibration results. By immersing the capillary thermostat in a well-regulated salt or oil bath, technicians can achieve a reliable reference temperature for calibration.
  1. Broad Temperature Range: Capillary thermostats are designed to operate within a wide range of temperatures, from sub-zero temperatures to high heat applications. Salt and oil baths can accommodate this broad temperature range, allowing technicians to calibrate thermostats for various temperature settings. Different types of salts or oils can be chosen based on the desired calibration temperature range, ensuring the accuracy of the calibration process across different operating conditions.
  1. Thermal Stability: Salt and oil baths offer excellent thermal stability, meaning that they can maintain a constant temperature over an extended period. This stability is crucial during the calibration process, as it enables technicians to observe the thermostat’s response accurately. By ensuring that the temperature remains constant during calibration, salt and oil baths provide reliable reference points for adjusting the thermostat’s setpoints.
  1. Avoidance of Ambient Interference: Calibrating capillary thermostats directly in ambient conditions can introduce environmental factors that affect accuracy. For instance, drafts, temperature fluctuations, and air currents can influence the thermostat’s performance. Immersing the thermostat in a salt or oil bath creates a controlled environment, shielding it from such ambient interference. This controlled setting allows technicians to focus solely on the calibration process, ensuring more precise results.
  1. Safety Considerations: Salt and oil baths also offer safety advantages during the calibration of capillary thermostats. When using oil baths, the high boiling points of certain oils, such as silicone oil, reduce the risk of evaporation and minimize the potential hazards associated with open flames or sparks. Additionally, salt baths can provide a safe medium for conducting high-temperature calibrations, as certain salts have high melting points that can withstand extreme temperatures.

How to know if a Salt Bath or Oil Bath should be used for the Capillary Thermostat Calibration

When calibrating a capillary thermostat, the choice between using a salt bath or an oil bath depends on several factors. Here are the key considerations to determine which option is more suitable for your specific calibration needs:358W-136 Capillary Thermostat

  1. Temperature Range: Evaluate the temperature range required for the calibration. Salt baths are generally suitable for lower temperature ranges (up to around 550°C or 1022°F) while oil baths can handle higher temperatures (up to approximately 300°C or 572°F). Consider the temperature range of your capillary thermostat and choose the bath that can accommodate it.
  2. Accuracy and Precision: Assess the required accuracy and precision for your calibration process. Salt baths typically offer better temperature uniformity and stability, resulting in higher accuracy. They are often preferred for more precise calibrations. Oil baths may have slightly lower accuracy but can still be suitable for many applications.
  3. Chemical Compatibility: Consider the chemical compatibility of the capillary thermostat and the bath medium. Salt baths use molten salts as the medium, and certain salts can react with or corrode certain materials. Oil baths, on the other hand, offer better compatibility with a wider range of materials. Ensure that the chosen bath medium does not damage or degrade the capillary thermostat during calibration.
  4. Safety and Environmental Factors: Evaluate safety considerations and environmental regulations. Salt baths operate at high temperatures and require proper safety measures to handle and dispose of the molten salts. Oil baths, particularly those using non-toxic and non-flammable oils, may have fewer safety and environmental concerns.
  5. Cost and Availability: Consider the cost and availability of the bath medium. Salt baths may require specific types of salts, which can be more expensive and less readily available compared to oils commonly used in oil baths. Factor in the cost and availability when making your decision.

Ultimately, the choice between a salt bath and an oil bath for calibrating a capillary thermostat depends on the specific requirements of your application, including temperature range, accuracy, chemical compatibility, safety, and cost. Assessing these factors will help you determine the most suitable bath medium for your calibration process.


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Bulb & Capillary Thermostats

Original equipment manufacturers worldwide use thermostat switches designed and manufactured by STEMCO, a Division of Senasys. No matter which style or model you choose, all of the capillary thermostat switches operate using the same physics. A fluid is encapsulated in a metal and when the temperature changes the fluid either expands or contracts. This fluid change moves a diaphragm which is in touch with a snap action switch and either opens or closes a circuit.

Ambient Compensation

Our capillary thermostats can be ambient compensated to offset the differential in temperature which keeps our thermostat controls more accurate as it’s environment changes.

Custom Options

Capillary thermostat switches built by Senasys can also be built to customer specifications. This insures you get the exact control you want without paying for features you don’t need.