Vacuum Sensor Selection: Gauge, Absolute and Output
Selection Guide
A vacuum sensor measures pressure below the surrounding atmosphere, but the right instrument depends on what the machine needs to know. For industrial selection, define the pressure reference, operating range and required output first. Monitoring suction in a handling system, measuring residual pressure in a process vessel and measuring very low chamber pressures can require different instruments.
Decide what the pressure reading means
A vented gauge-pressure sensor compares the process with the surrounding atmosphere. An absolute-pressure sensor uses a vacuum reference. A negative gauge reading and a positive absolute reading can therefore describe the same process condition. WIKA explains these pressure references.
For example, if local atmospheric pressure is 100 kPa absolute, a process at −80 kPa gauge is at 20 kPa absolute. This is an illustrative calculation: absolute pressure equals gauge pressure plus the local atmospheric pressure. Do not assume that local atmosphere is always exactly 100 kPa.
If the process specification defines a residual absolute pressure, choose a measurement referenced accordingly. WIKA identifies vacuum pumps and packaging processes among applications for absolute-pressure instruments. See WIKA’s explanation of absolute sensors.
Start with the application, then the specification
| Measurement task | What to clarify before choosing |
|---|---|
| Monitor suction in an automated handling circuit | Required switching point, vacuum range and controller input |
| Measure residual pressure in an evacuated process vessel | Absolute-pressure range, acceptable measurement uncertainty and process conditions |
| Measure very low pressure in a vacuum chamber | Suitable vacuum-gauge technology and its usable range |
This is a starting point for specifying an instrument, not a substitute for checking the selected model’s documentation.
Match the range and output to the exact variant
A family name is not enough to identify a vacuum sensor. As an example, the official Schmalz VSi page lists VSi V M8-4 at −1 to 0 bar, VSi VP8 M8-4 at −1 to 8 bar, and VSi P10 M8-4 at 0 to 10 bar. The same family includes different measuring ranges; its headline range does not describe every variant.
The VSi family is intended for automation and handling applications, with PNP/NPN switching and IO-Link features listed in the official overview. Check the exact part number and connection documentation for the required configuration. Compare the official VSi variants (datasheet pages 2–3).
Write down whether the receiving system needs a switching signal, a continuous measured value, or both. Then check the supply, electrical connection and signal specification together. A matching thread or similar display does not establish electrical interchangeability.
Know when a general pressure sensor is insufficient
Do not choose a general industrial pressure sensor for very low chamber pressure solely because its range starts at zero absolute. The usable measuring range and measurement principle still matter.
Pfeiffer distinguishes diaphragm, thermal-conductivity and ionization vacuum gauges, and explains that combined sensors can cover a wider range. Its application notes also identify pressure gradients, outgassing and contamination as possible influences on the reading. Use the gauge manufacturer’s range and installation guidance for the actual chamber. Read Pfeiffer’s vacuum measurement application notes.
Record these details before comparing models
- Task: suction monitoring, residual-pressure measurement or chamber measurement.
- Pressure: reference, units, normal range and lowest required reading.
- Performance: acceptable error at the operating point and required response.
- Process: gas or medium, temperature, contamination and connection.
- Interface: supply voltage, output type, connector and receiving equipment.
- Existing installation: full part number and the applicable datasheet or manual.
For broader process-instrument comparison, see our Rosemount, Yokogawa and Siemens pressure transmitter guide. Choose the measurement task and pressure reference before comparing transmitter families.