A pressure switch is made up of two parts: a sensor component and an electrical switch. The switch opens and closes a contact at a predetermined pressure known as the set point. The set point might be either fixed or variable. It is critical to select a pressure switch with a switch point in the right operating pressure range to ensure accuracy and lifespan. The specific features and capabilities vary according to the type of pressure switch.
What are the Types of Pressure Switches?
Pressure switches are classified into two types: electromechanical and solid state. Several types of sensors are used in electromechanical pressure switches. The sensor’s properties define the switch’s relative accuracy and lifetime and comprise the following types:
- Diaphragm switches are activated by a weld-sealed metal diaphragm. They can operate at up to 150 psi and have an accuracy of 0.5%.
- Bourdon tube switches employ a weld-sealed bourdon tube to activate the switch. The operating pressure ranges from 50 to 18,000 psi, with a 0.5% accuracy.
- Diaphragm piston switches havean elastomeric diaphragm, which acts on a piston. The piston then actuates the switch. Their operating pressure is from vacuum to 1600 psi, and accuracy is ± 0.2%.
- Piston switches use a piston to operate the switch. Their working pressure is 12,000 psi, and their precision is 0.2%.
- A diaphragm, metallic, or elastomeric sensor can be used in differential pressure switches. They have two pressure ports, one for high process pressure and one for low process pressure. The pressure differential between two sources is detected by the sensor, which activates the switch.
One or more switch points can be found in solid-state pressure switches. They not only open and close the pressure switch circuit, but they also have digital screens and can output analog or digital data. The majority of contemporary models are fully programmable and can communicate with a PLC or computer. Solid-state pressure switches have a broad range of operating pressures and frequency responses. They are highly resistant to shock and vibration with an accuracy of ±0.25%. In comparison to electromechanical pressure switches, they have much longer lifespans.
What are the Applications for Pressure Switches?
Pressure switches are widely used in a variety of sectors. They are commonly employed in the industrial control of equipment such as press machines, injection molding machines, and welding machines. Hydraulic and pneumatic pressure switches regulate truck air bellows and rail brake pressure. Industrial pressure switches are also used in a variety of automobile applications, such as engine oil monitoring, power steering, and transmissions. Pressure switches are used in medical equipment such as oxygen delivery systems to check the pressure of incoming gas.
The type of pressure switch housing used may impact whether or not it is suitable for use in various applications. Some pressure switches are not housed. They are most commonly employed when space or cost are important considerations. Housings are offered in a variety of materials to endure difficult situations where chemicals or corrosives may be present. Explosion-proof pressure switches use hefty housings to avoid ignition in flammable environments. These are typically found in the oil and gas industries.
The difference between the set point and the point at which the switch re-activates is referred to as deadband. To compute the deadband, the increasing and decreasing pressure set points must be verified. First, use an ohmmeter or digital multimeter to ensure that the pressure switch’s contact settings for “Normally Closed” (NC) or “Normally Open” (NO) are right. Connect the terminal to the NO circuit and read the data display to verify that it is the normally open circuit. Increase the setting until the contacts reverse and the meter shows the increased pressure setting. Then, starting at the highest set point, gradually lower the setting from NC to NO. The meter displays the decreasing pressure set point. Subtracting the increasing pressure set point from the decreasing one will provide the deadband.
The deadband might be fixed or adjustable as a proportion of the total pressure range. The deadbands of Bourdon tube and diaphragm switches are typically small, whereas piston switches have broad deadbands. Solid-state pressure switches can be modified to the full range of their capabilities. The dead band setting is critical in a system since it helps to prevent quick switching. This can have a negative impact on what the pressure switch controls and wear out the electrical contacts.
Adjustable deadband pressure switches allow for increased and decreased set point modifications. This may be necessary for changing conditions in order to optimize the switch’s accuracy and life expectancy. When electromechanical switches are operated in the upper quarter of their functioning range, the best precision is obtained. At the same time, working at the lower end increases longevity. The ideal compromise is to keep the switch in the middle operational. However, as operating conditions change, the switch points may need to be reset in order for the pressure switch to work optimally.
Delving into the concept of deadband in pressure switches sheds light on a crucial aspect of their functionality. By understanding and optimizing deadband, we can ensure these devices operate effectively, promoting safety, reliability, and efficiency in various applications. A solid grasp of deadband is essential for making the most out of pressure switches.