Remote Bulb Temperature Control: A Basic Introduction

Remote bulb temperature control is a type of mechanical temperature control that uses a capillary tube and a sensor to regulate the temperature of a medium (such as air, water, or gas) at a distance from the control unit. This allows for more precise and flexible temperature control in applications where the control unit cannot be located near the medium or where the medium temperature varies widely.

How does it work?

A remote bulb temperature control consists of three main components: a control unit, a capillary tube, and a sensor (also called a bulb). The control unit is a device that contains a set point dial, a switch, and a pair of contacts that open or close depending on the temperature. The capillary tube is a thin metal tube that connects the control unit to the sensor. The sensor is a sealed metal capsule that contains a liquid that expands or contracts with temperature changes.

The principle of operation is based on the thermal expansion of the liquid in the sensor. As the medium temperature increases, the liquid in the sensor expands and exerts pressure on the capillary tube. This pressure is transmitted to the control unit, where it moves a diaphragm or a bellows that operates the switch. The switch then opens or closes the contacts, which control the power supply to the heating or cooling device. Conversely, as the medium temperature decreases, the liquid in the sensor contracts and reduces the pressure on the capillary tube. This causes the switch to reverse its action and change the state of the contacts.

What are the advantages and disadvantages?

Remote bulb temperature control has several advantages over other types of temperature control, such as:

  • It can measure and control the temperature of a medium that is far away from the control unit, up to several meters or even hundreds of meters.
  • It can measure and control the temperature of a medium that has a large temperature range, from below freezing to above boiling.
  • It can measure and control the temperature of a medium that is inaccessible, hazardous, or corrosive, such as steam, refrigerant, or oil.
  • It can provide proportional control, which means that the switch action is proportional to the temperature deviation from the set point, rather than on-off control, which means that the switch action is either fully on or fully off. This results in more stable and accurate temperature control.

However, remote bulb temperature control also has some disadvantages, such as:

  • It is more expensive and complex than other types of temperature control, especially for long capillary tubes and sensors.
  • It is more prone to errors and failures due to leaks, kinks, bends, or damage to the capillary tube or the sensor.
  • It is more sensitive to ambient temperature changes, which can affect the pressure in the capillary tube and the sensor. Therefore, it requires proper insulation and calibration.

How to choose and install a remote bulb temperature control?

There are many factors to consider when choosing and installing a remote bulb temperature control, such as:

  • The type and size of the medium to be controlled, which determines the type and size of the sensor and the capillary tube.
  • The temperature range and accuracy required, which determines the type and range of the control unit and the sensor.
  • The distance and location of the medium from the control unit, which determines the length and routing of the capillary tube.
  • The environmental conditions, such as humidity, vibration, and corrosion, which determine the material and protection of the control unit, the capillary tube, and the sensor.

Some general guidelines for installing a remote bulb temperature control are:

  • Follow the manufacturer’s instructions and specifications for the control unit, the capillary tube, and the sensor.
  • Mount the control unit in a convenient and accessible location, away from heat sources, moisture, and vibration.
  • Mount the sensor in a representative location of the medium, where it can sense the average temperature and avoid hot or cold spots.
  • Route the capillary tube carefully, avoiding sharp bends, kinks, or damage. Secure the capillary tube with clamps or brackets at regular intervals. Insulate the capillary tube if necessary.
  • Connect the control unit to the power supply and the heating or cooling device according to the wiring diagram. Test the operation and adjust the set point as needed.

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