What is a pressure switch

A pressure switch is a simple pressure control device commonly used in control systems; when the measured pressure reaches the set value, it can emit an alarm or a control signal.

Working principle of the pressure switch: When the measured pressure exceeds the rated value, the free end of the elastic element moves, which directly or after comparison pushes the switching element, changing its on/off state and thus achieving control over the measured pressure. The elastic elements used in pressure switches include single-coil helical springs, diaphragms, bellows, and corrugated tubes. Switching elements include magnetic switches, mercury switches, microswitches, etc. The switching types of pressure switches are normally open and normally closed. Pressure switches are used in commercial, industrial, automotive, and household applications.

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Pressure switches are typically used in secondary circuits to turn things on or off, thereby protecting the equipment. It usually has one pair of normally open contacts and one pair of normally closed contacts, which are selected for use according to the requirements of the circuit. The pressure switch we are referring to is a field pressure protection device that changes its state once the system pressure exceeds the set value; at the same time, a signal is sent to the control room or the local control panel, so as to enable interlocking or alarm functions for the device.

I work in the field of process engineering; I only know that it’s a type of instrument used in DCS systems for interlock functions, as well as for generating alarms when pressure is too low or too high. Once the interlock is activated, it will trigger an action as soon as the pressure reaches the set value specified by the pressure switch, thereby protecting the chemical processing equipment and causing an emergency shutdown of the system.

A pressure switch is a device that activates a switch when the pressure reaches a certain level. (There are also cases where the switch is triggered when the pressure reaches a certain level.) In simple systems, the pressure switch is likely to be mechanical; it operates through the displacement of elastic elements such as springs, diaphragms, or bellows, which in turn actuate the switch. It may also involve piezoelectric crystals that directly generate a signal current to activate the switch. In the case of a control system, broadly speaking, any situation in which the pressure measurement value at a certain point is used as a signal to activate a switch that may be located quite far away – whether it’s simply a switch or a valve or some other device – can be considered a pressure switch.

Principle of pressure switches: A pressure switch is a simple pressure control device that can emit an alarm or a control signal when the measured pressure reaches the set value. The working principle of a pressure switch is as follows: when the measured pressure exceeds the rated value, the free end of the elastic element moves, which directly or after comparison drives the switching element, thereby changing its on/off state and achieving control over the measured pressure. The elastic elements used in pressure switches include single-coil helical springs, diaphragms, bellows, and corrugated tubes. Switching elements include magnetic switches, mercury switches, microswitches, etc. The switching types of pressure switches are normally open and normally closed. Pressure switches are used in air compressors primarily to control their start and stop operations. By adjusting the pressure within the air storage tank, the compressor can be stopped to allow it to rest, which helps in maintaining its condition. During factory calibration of the air compressor, the pressure is adjusted to the specified value according to the customer’s requirements, along with a certain pressure difference being set. For example, when the compressor starts and fills the air storage tank, it stops or switches to unload mode once the pressure reaches 10 kg; it then starts again when the pressure drops to 7 kg. This pressure difference allows the compressor to rest, thereby protecting it. The compressor is driven directly by an electric motor, which causes the crankshaft to rotate, thereby moving the pistons back and forth and resulting in changes in the volume of the cylinders. Due to changes in the pressure inside the cylinder, air passes through the intake valve and via the air filter (silencer) into the cylinder. During the compression stroke, as the volume of the cylinder decreases, the compressed air exits through the exhaust valve, and then passes through the mass flow meter and the check valve into the air storage tank. When the exhaust pressure reaches the specified value of 0.7 MPa, the pressure switch activates to shut down the system automatically. When the pressure in the gas storage tank drops to 0.5–0.6 MPa, the pressure switch activates automatically. With the rapid development of electronic and information technologies, pressure measurement and automatic control techniques have become integral to various aspects of people’s lives and work. As one of the methods for controlling pressure, pressure switches are no longer limited to simple on/off control at a specific pressure level; instead, they are capable of detecting pressure levels, allowing for continuous setting of control points, as well as enabling remote signal transmission. As a result, electronic pressure switches are gradually replacing various mechanical pressure switches and have become the mainstream choice in applications. Basic principle of electronic pressure switches: Electronic pressure switches primarily use pressure sensors to sample pressure. These sensors convert the non-electrical quantity of pressure into electrical quantities that can be measured, namely voltage or current. The sensor signals are then amplified and processed by signal conditioning circuits. Finally, through a comparison circuit, the device outputs a signal at a certain logical level when the preset pressure threshold is reached; this logical level can be fed into a microcontroller to drive subsequent circuits or control electrical switches. Users can determine the pressure value at which the pressure switch operates by setting a level conversion threshold; moreover, the mass flow meter can enable real-time monitoring of pressure and its remote transmission by amplifying and processing the electrical signal. The electronic pressure switch DS200 features a precision pressure transmitter, an intelligent pressure switch, and a digital display function. Its application areas span from gas dynamics to hydraulics, and it is also widely used in the field of precision control. Its notable feature is its stability. The DS200 can be used in any gas and liquid measurement system that is compatible with stainless steel and FKM. The system pressure is displayed by four-digit LEDs. In addition, the DS200 also supports setting protection via buttons on the display panel, as well as on-site programming for functions such as display settings and switch outputs. The setting point can be freely adjusted within the 0–100% range at atmospheric pressure. The display and housing can rotate freely to facilitate the installation of the instrument in special locations. The NS-P2 pressure switch provided by the Marketing Center Network features the following advantages: compact and attractive design for easy installation; high precision with stable output signals; resistance to vibrations and interference; programmability; wide application in the field of automatic pressure control; real-time display of both the set pressure value and the current pressure value; fast response speed; ability to set upper/lower limit values as well as hysteresis/offset values

A pressure switch is essentially a pressure gauge that failed during manufacturing, so it had to be designed to provide digital output.

Working principle of pressure switches: Generally, a \"electrical contact pressure gauge\" is used, which is a regular tube-spring pressure gauge equipped with two sets of electrical contacts. It can connect electrical contacts at relatively high and low pressures, thereby controlling the pressure within upper and lower limits. This type of electrical contact has a low capacity and can only switch the control coil of the contactor; the control position on the pressure gauge can be adjusted. 　　A pressure switch is a simple pressure control device that can emit an alarm or a control signal when the measured pressure reaches the set value. 　　The working principle of a pressure switch is as follows: when the measured pressure exceeds the rated value, the free end of the elastic element moves, which directly or after comparison drives the switching element, thereby changing its on/off state and achieving control over the measured pressure. 　　The elastic elements used in pressure switches include single-coil helical springs, diaphragms, bellows, and corrugated tubes. 　　Switching elements include magnetic switches, mercury switches, microswitches, etc. 　　The switching types of pressure switches are normally open and normally closed. 　　The adjustment methods for pressure switches are two-position and three-position. 　　Accuracy: A value that indicates the precision of a device, including linearity, tolerance, hysteresis, repeatability, etc. Currently, the highest precision of pressure switches in Nagano reaches ±0.5% F.S., with the model being CB33. 　　Max Pressure (Max.P): The maximum value within the pressure range. 　　Full Scale (F.S): The difference between the maximum and minimum values of the pressure range. 　　On-off difference (dead zone): refers to the difference between the set operating value and the reset value of a switch. For example, if the set value is 1 MPa and the actual reset value is 0.9 MPa, then the on-off difference is 0.1 MPa. 　　Operating temperature: refers to the temperature range within which the internal components and sensitive elements of the instrument do not undergo sustained deformation during operation. The recommended operating temperature range for standard pressure switches is -5 to 400°C. If the temperature of the medium is too high, a suction tube (funnel-shaped) can be used as an accessory to help reduce the temperature. 　　S.P.D.T (Single Pole Double Throw): It consists of one normally open contact, one normally closed contact, and a common terminal. 　　D.P.D.T (Double Pole Double Throw): It consists of a symmetrical left and right common terminal, along with two sets of normally open and normally closed terminals. 　　Upper limit contact (normally open): When the pressure rises to the set value, the contact activates and the circuit is closed. 　　Lower limit contact (normally closed): When the value drops to the set level, the contact activates and the circuit is closed. 　　Upper and lower limit contacts HL: It is a combination of upper limit and lower limit functions, and comes in two types – independent operation of the two contacts (double setting, double circuit) and simultaneous operation of the two contacts (single setting, double circuit). 　　2-contact upper limit: It combines two types of upper limits, divided into two categories – independent operation of the two contacts (double setting, double circuit) and simultaneous operation of the two contacts (single setting, double circuit). 　　Lower limit 2 contacts: It combines two lower limit configurations, divided into two types – independent operation of the two contacts (double setting, double circuit) and simultaneous operation of the two contacts (single setting, double circuit). 　　Pressure rating: The maximum pressure that a pressure switch can withstand while maintaining its normal performance. However, when a pressure switch is used in overpressure applications, the sensitive element will undergo continuous deformation, causing the pressure setting to change; as a result, the pressure switch will be unable to function properly and may even get damaged. 　　IP (Protection Rating): It is a standard established by the International Electrotechnical Commission (IEC) that specifies the dust and moisture resistance capabilities of lighting fixtures.