How Oil Free is your compressed Air?

Oil monitoring & control systems for compressed air installations

Having an oil free compressor does not necessarily mean that your compressed air is oil free as the term “oil-free compressor”  refers only to the compression chamber, not the compressor system as a whole, or the resulting compressed air quality.

Contaminants in the compressed air system generally can be attributed to:
The quality of the air drawn into the compressor
The operation of the air compressor
Compressed air storage devices and distribution systems

Keep in mind that most of the millions of particles in normal urban ambient air your compressor sucks in, are below the pore size of the compressor inlet filters. Hydrocarbon content in ambient air varies from area to area but is often sufficient to contaminate the compressed air of your system. Ofcourse, the answer to that, is an air treatment system downstream, but how do you know that your air quality complies with the requirements of oil free air 24hours/day 365 days/year?

Many industrial processes are very sensitive to oil contamination, as this can lead to downtime, product spoilage & recall, damage the company's reputation, harmed consumers & product liability, but up to now the only method for measuring the in-pipe oil content involved specialist equipment and  a time-consuming laboratory analysis.

Online measuring and monitoring device for compressed air oil content

Sigma 120 compressed air Oil Monitor

with 5" touch screen, 0.003 mg/m³, 4...20 mA output, RS-485, alarm output, 24 VDC

The new residual oil monitor Sigma 120 monitors oil contents of compressed air and gases for spot checks when used as portable unit in conjunction with S 551. The simple installation and the outstanding performance makes Sigma 120 the ideal choice when residual oil contents needs to be measured and monitored.

Oil free compressed air is not an easy task to be achieved. Monitoring is a must in many industries and applications to avoid contaminations in products and risks for health of humans. S 120 makes this monitoring task affordable and reliable.

For best accuracy and long term stability, the sensor applies an automatic calibration. Sensor contaminations and sensor life time are monitored and will be indicated to the user. An over range detection will remove the sampling air from the sensor to protect it against contamination.

Limits of oil vapor

Compressed air class 1 (EN ISO 8573-1): 0.01 mg/m³
Medical applications (EAB 407/1238): 0.1 mg/m³
Breathing apparatus (EN 12021): 0.5 mg/m³


Measures residual oil contents in compressed air and other gases
Can be used for permanent or in portable applications
Measures down to 0.003 mg/m3
Easy connection through sampling hose and quick connect
Output signals:
- 4...20 mA
- RS-485 / Modbus / RTU
- Relay switch (NO)
PID sensor for highest accuracy
Service and Alarm indication through LED
Connectable to our displays and data loggers as well as third parties displays and control units


Medical air
Breathable air
Marine air
Food and beverage
Medical engineering
High speed trains
Semiconductor fabs
Conveyance of hygroscopic food
High tech processes
Electronics industry

Technical information
Measuring range: -0.001...10 mg/m3
Sensor type: PID (photoionization detector)
Medium: Clean dry compressed air
Operating pressure: 3 ... 15 barg
Sample flow rate: < 2 l/min
Life time sensor: Requires service once a year
Gas temperature: -20...40 °C
Ambient temperature: -20...40 °C