Selection of the measurement range for vacuum pressure switches

The selection of the measurement range for vacuum pressure switches should be based on specific application scenarios, equipment characteristics, and process requirements. Comprehensive considerations should be made from dimensions such as pressure range, accuracy requirements, environmental compatibility, and long-term stability. The following are the key points for specific selection:

First, clearly define the pressure requirements of the application scenarios

The distinction between coarse vacuum and high vacuum

Coarse vacuum (10³ to 1 Pa) : Commonly used in food packaging, vacuum drying and other processes, it is necessary to select a switch with a range covering -100 kpa to 0kPa to ensure stable operation within the range of -90 kpa to -10 kpa.

High vacuum (10⁻¹ to 10⁻⁶ Pa) : For applications such as semiconductor manufacturing and electron beam welding, ultra-high vacuum compatible models should be selected. The range may extend to -10⁻³ Pa (absolute pressure) or even lower, and it is necessary to confirm whether it supports full-range calibration.

Mixed working condition of positive pressure and negative pressure

If the system needs to monitor both positive pressure (such as compressed air) and negative pressure (such as vacuum adsorption) simultaneously, a dual-range or compound range switch should be selected. For instance, models with a measurement range from -100 kpa to +1MPa can meet the pressure monitoring requirements of vacuum generators and pneumatic actuators.

Second, match the technical parameters of the equipment

Pressure fluctuation range

Select the range margin based on the pressure fluctuation amplitude during the operation of the equipment. For instance, if the start and stop of the vacuum pump cause the pressure to fluctuate between -80 kpa and -60 kpa, it is recommended to select a switch with a range of -100 kpa to 0kPa to avoid frequently approaching the range limit.

Response speed and hysteresis requirements

For high-speed processes (such as vacuum coating), a switch with a small hysteresis (such as ±1kPa) should be selected, while for low-speed processes (such as vacuum impregnation), a hysteresis of ±5kPa is acceptable. Excessive hysteresis will lead to a decrease in control accuracy, while too little may cause misoperation.

Output signal and control logic

Select the output type according to the requirements of the control system:

The mechanical contact type is suitable for directly driving relays or solenoid valves.

The analog signal type (4-20mA) is convenient for integration with PLC or DCS.

Digital signal types (such as Modbus RTU) support remote parameter setting and diagnosis.

Third, assess the compatibility between the environment and the medium

Medium characteristics

Corrosive medium: If the medium contains acid, alkali or organic solvents, corrosion-resistant materials (such as Hastelloy diaphragms, PTFE seals) should be selected.

Cleanliness requirements: Pharmaceutical or semiconductor equipment should be equipped with oil-free and particle-free switches to prevent product contamination.

Environmental temperature and humidity

For high-temperature environments (such as above 120℃), high-temperature resistant models should be selected, and their elastic elements and electronic components need to pass high-temperature aging tests.

In a humid environment (such as 95%RH), it is necessary to confirm the protection level (such as IP67) and sealing performance to prevent internal condensation.

Vibration and Shock

When installing on equipment with intense vibration (such as centrifuges and vibrating screens), anti-vibration type switches should be selected, and their internal structures need to pass vibration tests (such as 10g acceleration and 10-2000Hz sweep frequency).

Fourth, consider long-term stability and maintenance costs

The range and accuracy are balanced

High-precision requirements (such as ±0.5%FS) are usually accompanied by rising costs and need to be weighed according to process requirements. For instance, the temperature uniformity control of a vacuum furnace may require an accuracy of ±0.1%FS, while for a general vacuum packaging machine, ±1%FS is sufficient.

Calibration and maintenance cycle

The calibration cycle of mechanical switches is usually long (such as 2 to 3 years), but the wear of the contacts needs to be checked regularly.

Electronic switches may need to be calibrated annually, but they support self-diagnostic functions that can provide early warnings of performance degradation.

Spare parts and Compatibility

Choosing switches with standardized ranges can reduce the cost of spare parts. For example, -100 kpa to 0kPa is a common range, and the spare parts inventory is sufficient. Non-standard measurement ranges may lead to an extension of the procurement cycle.

Fifth, examples of range selection in typical application scenarios

Food vacuum packaging machine

Range: -100 kpa to 0kPa

Accuracy: ±1%FS

Output: Mechanical Contact (SPDT

Reason: To cover the vacuum degree range required for the packaging process, the mechanical contacts directly drive the sealing mechanism.

Semiconductor etching equipment

Range: -10⁻³ Pa to 10⁵ Pa (absolute pressure)

Accuracy: ±0.1%FS

Output: Digital signal (Modbus)

Reason: It is necessary to monitor both high vacuum and atmospheric pressure simultaneously, and digital signals facilitate integration with the equipment control system.

Pharmaceutical vacuum drying oven

Range: -95 kpa to -5 kpa

Accuracy: ±0.5%FS

Material: 316L stainless steel +PTFE sealed

Reason: It meets the vacuum degree requirements for drug drying, and the corrosion-resistant material complies with GMP standards.

Sixth, avoid common misunderstandings

Too narrow range: If only the normal operating pressure is considered while the pressure fluctuation is ignored, it may cause the switch to act frequently or get damaged.

Neglecting medium compatibility: Failing to confirm whether the material is corrosion-resistant may lead to switch leakage or failure.

Excessive pursuit of precision: Using high-precision switches in non-critical processes will increase costs and raise the complexity of maintenance.