Vacuum

This guide provides an overview of measuring vacuum pressure including suggested vacuum measurement products and question & answers relating to using and selecting vacuum measurement sensors & instrumentation.

Products

Vacuum range pressure transducers, transmitters, gauges, loggers, calibrators and hand pumps for measuring negative gauge suction or absolute pressures below ambient atmospheric pressure.

• Vacuum Pressure Transducers - These voltage output transducers will provide a linear signal of a few volts that is directly proportional to a specified vacuum range.
• Vacuum Pressure Transmitters - Choose vacuum pressure transmitters for measurements over the low vacuum range of 25 to 760 Torr, using a absolute or negative gauge reference vacuum range.
• Vacuum, Suction Pressure Data Loggers, Recorders - Vacuum data loggers for recording negative suction pressure or absolute pressure below atmospheric pressure. Log and store vacuum measurements for printing test reports or analysing process trends.
• Vacuum, Suction, Negative Pressure Gauges - Vacuum range gauges for measuring absolute vacuum or suction pressures which can be permanently installed or used as a test gauge.

4-20mA Output Vacuum Pressure Transmitters

Vacuum pressure transmitter with a 4-20mA 2 wire current loop output for measuring suction pressures relative to atmospheric pressure or absolute zero referenced pressures.

• DPS Low Differential Pressure Transmitter
• DMP331P Hygienic Flush Pressure Transmitter
• LEO3 Current or Digital Output Pressure Gauge
• DS200P Sanitary Low Range Pressure Gauge, Switch and Sensor
• DMK457 Marine Approved Pressure Transmitter
• DMP331i High Accuracy Pressure Transmitter
• DMK331P Flush Diaphragm Pressure Sensor
• DMP343 Low Range Pneumatic Pressure Sensor
• DMP457 Marine Approved Pressure Transmitter
• XMPi Process Plant Gauge and Absolute Pressure Transmitter
• DPS200 HVAC Differential Pressure Transmitter
• DPS300 User Switchable Pressure Range, Volts or Current Output Low DP Sensor
• DS200 Combined Pressure Switch, Gauge and Sensor
• DS210 Combined Low Pressure Switch, Indicator and Sensor
• 25 Ed Flame Proof Flush Diaphragm Pressure Transmitter

Voltage Output Vacuum Pressure Transducers

Vacuum Range Pressure transducers with 5 or 10 volt full rnage output signals for measuring partial vacuums of a few mbar or full vacuums up to minus 1 bar (-15 psi).

• DPS Low Differential Pressure Transmitter
• DMP331P Hygienic Flush Pressure Transmitter
• DS200P Sanitary Low Range Pressure Gauge, Switch and Sensor
• DMP331i High Accuracy Pressure Transmitter
• DMK331P Flush Diaphragm Pressure Sensor
• DMP343 Low Range Pneumatic Pressure Sensor
• DPS200 HVAC Differential Pressure Transmitter
• DPS300 User Switchable Pressure Range, Volts or Current Output Low DP Sensor
• DS200 Combined Pressure Switch, Gauge and Sensor
• DS210 Combined Low Pressure Switch, Indicator and Sensor
• 25 Ed Flame Proof Flush Diaphragm Pressure Transmitter

Millivolt Output Vacuum Pressure Sensors

Vacuum range strain gage pressure sensors with mV output signals for measuring pressures below ambient air pressure with a gauge or absolute reference.

Digital Vacuum Pressure Sensors

Vacuum range digital interface pressure sensors for connecting to computer serial bus or other intelligent interface.

• 33X High Accuracy Digital Output Pressure Sensor
• LEO3 Current or Digital Output Pressure Gauge
• 35X Flush Diaphragm Digital Output Pressure Sensor

Switches for Controlling Vacuum

Pressure switches for starting & stopping equipment or sending an alarm signal at a preset vacuum pressure.

• DS200P Sanitary Low Range Pressure Gauge, Switch and Sensor
• DS200 Combined Pressure Switch, Gauge and Sensor
• DS210 Combined Low Pressure Switch, Indicator and Sensor
• 901 Prescal Pressure Switch Specification and Data Sheet

Gauges for Measuring Vacuum

Vacuum range pressure gauges with digital readout for measuring absolute vacuum or suction pressures which can be permanently installed or used as a test gauge.

• Baroli 02 Precision Digital Pressure Gauge
• LEO3 Current or Digital Output Pressure Gauge
• LEX1 (Ei) High Accuracy Digital Pressure Gauge
• LEO Record (Ei) Pressure Data Logger
• LEO1 (Ei) Digital Pressure Gauge
• DS200P Sanitary Low Range Pressure Gauge, Switch and Sensor
• DM01 Multi-Range High Accuracy Pressure Gauge
• LEO 2 (Ei) Digital Manometer
• Baroli 05 Industrial Digital Pressure Gauge
• DS200 Combined Pressure Switch, Gauge and Sensor
• DS210 Combined Low Pressure Switch, Indicator and Sensor
• Baroli 02P Low Range Flush Diaphragm Digital Pressure Gauge

Data Loggers for Measuring Vacuum

Vacuum data loggers for recording negative suction pressure or absolute pressure below atmospheric pressure. Log and store vacuum measurements for printing test reports or analysing process trends.

• LEO Record (Ei) Pressure Data Logger
• DM01 Multi-Range High Accuracy Pressure Gauge

Calibration Equipment for Vacuum Range

Calibration pumps for generating vacuum pressures to check vacuum reading accuracy of sensors, gauges and switches with a master vacuum test gage.

• LEX1 (Ei) High Accuracy Digital Pressure Gauge
• DM01 Multi-Range High Accuracy Pressure Gauge
• PGS40 Mid Pressure Calibration Hand Pump

Vacuum Measurement

Vacuum is the range of pressure which lies between absolute zero pressure and atmospheric pressure.

Vacuum pressures in the range of a few millibars up to atmospheric pressure are easily measured by diaphragm based pressure measurement instrumentation. In this range of partial vacuum pressures it is common to measure the vacuum using either a negative gauge reference or an absolute reference pressure sensing device. The choice of a negative gauge or an absolute reference will depend on whether you are interested in measuring the pressure compared to atmospheric pressure or to a perfect vacuum.

High vacuum pressures are very close to zero absolute pressure and much harder to measure with diaphragm type instrumentation. At high vacuum pressures it is necessary to use different sensor technology which is based on ionisation or thermal conductivity measurement principles.

Vacuum pressures are generated in many applications within the research and industrial sectors which include gas/vapour removal, leak testing, pick-up tools, sterilization, semiconductor processing and altitude simulation.

Help Guides

Articles with more information on vacuum measurement products & applications.

• Measuring vacuum with negative gauge or absolute ranges
• What is the difference between vacuum and absolute pressure
• What does negative and positive gauge pressure mean
• Suction Pressure
• Output signal orientation for a negative gauge pressure range
• Measuring negative pressure using a positive differential pressure range
• Can you have a minus 20 psi gauge vacuum measurement range
• Can you measure vacuum using a gauge pressure range
• Negative Gauge Pressure

Questions & Answers

0 bar absolute = -1 bar gauge

Is zero bar absolute the same as minus 1 bar gauge?

No, only when atmospheric pressure happens to correspond exactly to 1 bar absolute which rarely happens.

Does 1 bar cover the vacuum range

Is a minus 1 bar range adequate for measuring over the vacuum range?

For most applications yes, especially if measuring low suction pressures.  If measuring a very high vacuum to some degree of accuracy, it is best to measure with a positive absolute range, since a negative gauge device will give different readings due to the changes in atmospheric pressure.

Technology used to measure over vacuum range

What type of sensing technology is used for measuring in the vacuum range?

For vacuum ranges 0-100 mbar up to 0-1000 mbar absolute it is usual to use a lower cost strain gauge diaphragm type.  For ranges from 0-1 mbar up to 0-1000 mbar absolute, capacitive or inductive sensing techniques are the typical methods for measuring higher vacuums more precisely and with less drift.   For ultra high vacuum ranges below 0-1 mbar it is not possible to measure this low a pressure with electromechanical devices and it is necessary to use less direct methods such as thermal conductivity and ionisation techniques.

Vacuum units

What pressure units are used for measuring vacuum pressures?

• Low vacuum: psi, mbar, kPa, inHg and mmHg
• High vacuum: Torr, Pa, mmHg, mbar

Vacuum level variations in a pumped chamber

Will the vacuum level be the same at the opposite end to the suction end of a chamber where a vacuum pump is connected?

If there is flow of gas, then you should expect there to be some difference in pressure, but it will depend on flow rate, size of volume and any restrictions between pump and end of chamber. If the suction pressure is static with no flow, then the vacuum pressure will equalise it all points.

Vacuum Gauge vs Vacuum Absolute

What is difference between reading pressure in vacuum gauge and vacuum absolute?

Vacuum gauge is measured from ambient air pressure in the negative direction. So for example at ambient air pressure the vacuum reading is 0 bar gauge and if a suction pressure of 0.25 bar is applied, the vacuum reading will be -0.25 bar gauge.

Vacuum absolute is measured from a perfect vacuum in the positive direction. At ambient air pressure the vacuum reading will be the barometric air pressure, let’s use 1.015 bar absolute as an example. If a suction pressure of 0.25 bar is applied the vacuum reading will be 0.765 bar absolute.