Why monitor compressed air?

Leaks waste energy and money
At a time of increasingly rising energy costs, it is even more important to exploit potential savings in order to remain competitive. Many users of compressed air have no idea how high the total consumption of compressed air is and hence are unaware of the extent of the cost of leaks.

The efficiency of a compressed air supply system begins with the generation of compressed air and ends with the consumer. Loss of compressed air through leaks in the pipe network generates extremely high costs and reduces efficiency. Until now these costs were hidden in the overall electricity bill and were not transparent.   Complete transparency usually prevails in all companies with regard to the consumption of most other mediums such as electricity, water and gas. Water meters, for example, indicate the exact water consumption. In contrast to compressed air, water leaks are immediately visible to everyone and are repaired straight away whilst air continues to escape unnoticed from leaks in the compressed air network even at the weekend and during shutdowns.    The compressors continue to turn blithely during this period just to maintain constant pressure in the network.  These observations do not cover the cost of “generating clean, dry“ compressed air. Refrigeration driers and adsorption driers dry the air at considerable running costs, for it then to be just carelessly wasted.

This chart indicates the costs and energy loss associated with leaks. An undetected hole as small as 5mm can cost a plant €16,176 per year. Leaks are only audible when larger than 1mm² at a pressure of 7 bar. Predictive leak detection and repair will result in substantial cost savings and system efficiency.

Hole Diameter Air Leakage Euro lost
1mm 1,8 l/s € 480/year
3mm 20,8 l/s € 6.096/year
5mm 58.5 l/s € 16.176/year
10mm 235,2 l/s € 63.360/year

How are the leaks detected?
Our sensors monitor air consumption to detect leakage areas in two ways

  • Method 1: when machine is in operation the sensor compares the machine’s ideal air consumption to the actual air consumption. The difference indicates an air leakage.
  • Method 2: when machine is shutdown the sensor continuously monitors the machine during shutdown. Any air consumption that is measured indicates an air leakage.

Our sensor can also monitor

  • Leakage per individual machine
  • Leakage per zones in a plant
  • Consumption per machine cycle
  • Consumption per shift
  • Consumption per zones in a plant

Verification of leak repair and system improvements
Dividing a plant into zones is key to leak detection
In order for the sensor to provide predictive maintenance information, a plant should be first divided into zones based on the number of fittings and potential leakage points. After sectioning a plant into smaller, more manageable zones, the sensor is mounted in the supply line to the zone. The sensor will detect leakage areas based on the zone’s increase in air consumption over time or monitor air consumption when machines in the zone are shut down.

After a leakage area is detected, leak repair can occur quickly.
The sensor will target a leakage area by zone so that plant personnel can focus on a specific, smaller area, rather than search an entire plant for air leaks. With the zone identified, maintenance can quickly pinpoint the exact leak location and repair the leak. The best method for this is to use an ultrasonic acoustic detector and follow up with soap and water applied to the suspected leak.

A predictive maintenance sensor   

The C420 series give you a compact compressed air  consumption measurement unit with display and totalizer function. A valuable aid to detect leakage areas.

The consumption sensor C420 is based on the thermal mass flow principle. It measures volumetric standard flow over a wide measuring range. The result is pressure and temperature independent. C420 is an in-line type sensor which is mounted into the pipe. There are 7 models available for ¼”, ½”, ¾”, 1” , 1 ¼”, 1 ½”, and 2” tubes. The version with display shows the actual volumetric flow and the total consumption. The consumption counter can be set via the keyboard. Various settings such as gas type, flow unit, reference standards, can be set ex factory or through our service kit. The service kit consists of a PC software and a interface box which connects the sensor to the USB port of the PC. Every sensor includes an analogue output (4…20mA) for flow and an isolated pulse output for the consumption counter.


  • In-line type for high accuracy in small tube diameters.
  • Analogue output 4...20 mA, pulse output (galvanically separated).
  • Particular suitable for measuring process gases such as N2, Ar, He etc.
  • Thermal mass flow, independent of pressure and temperature changes
  • Easy installation
  • Very fast response time

Applications for C420

  • compressed air balancing
  • compressed air consumption measurement
  • leakage air / leak rate determination
  • mobile compressed air measurement in front of single machines / plants
  • flow measurement of process gases like e. g. nitrogen, CO2, oxygen, argon, nitrous oxide
  • flow measurement at nitrogen generators


Technical data

C420  Measured units  m3/h, m3/min, l/min, cfm

Accuracy  +- (2% of measured value + 0.3% full scale)

Medium  Air,  non explosive gases (N2, O2, CO2, N2O, Ar)

Operating temperature  -30 ... 80 ºC

Operating pressure  Up to 16 bar  (optionally up to PN 40)

Analogue output  Signal: 4 ... 20 mA

Scaling: 0 ... max range

Pulse output  1 pulse per m3

Power supply  24 VDC smoothed ± 15 %

PC connection: SDI interface

Mounting thread meas. section: R 1/4", R 1/2", R 3/4"R 1", R 1 1/4", R 1 1/2", R 2" external thread

Volumetric Flow Ranges
Inner tube  Measuring range
inch dia (mm) from to
1/4" 8.5 0.8 90 l/min
1/2" 16.1 0.2 90m3/h
3/4" 21.7 0.2 170 m3/h
1" 27.3 0.2 290 m3/h
1 1/4" 36.8 0.7 480 m3/h
1 1/2" 41.8 1.0 550 m3/h
2" 53.1 2.0 900 m3/h



Humidity control: How to prevent damage
The modern production technology needs compressed air. The diversity of application starts with non processed blast air to absolute dry, oil-free and sterile compressed air. Irrespective of how it is used, compressed air has to be dry. Depending on the application considerable economical damage can be caused by uncontrolled „humidity irruption“ into the compressed air system.

Reasons that can lead to an increased pressure dewpoint value within the compressed air system

  • Condensate at the refrigeration dryer (condensate eliminator faulty or dirty)
  • Condensate overload of the refrigeration dryer
  • Adsorption agent is not regenerated sufficiently
  • Compressed air bypass in the bypass (valve faulty or not closed)
  • Compressed air bypass in the refrigeration dryer (worn out, corroded etc.)

  Water in compressed air leads to damages

  • Corrosion within the pneumatic plant -Rust will develop in the ducts and functioning elements and will lead to leakages.
  • Breakage of the lubricating film – Broken lubricating films lead to mechanical faults.
  • Building of electric elements.
  • Formation of ice in the compressed air system - At low temperatures the water within the compressed air system  could freeze and cause frost damage, reduction of the diameter and blockades.
  • Material handling - High humidity leads to conglutination of materials to be transported, e. g. sugar, concrete, granulate, etc.
  • Pharmaceutical -High humidity impairs powders, tablets, etc.
  • Hospital - DIN 13260, EN 737-3, danger of development of bacteria

What is pressure dewpoint and how it affects air quality?
Dew point measuring is an effective way of determining the amount of vapour contained in a gas. It is the specific temperature, at a given pressure, under which vapour condensates to water. Increasing the pressure of a gas also increases its dewpoint temperature.

According to Dalton’s law, in any mixture of gases, the sum of the partial pressures of the component gases equals to the total pressure of the mixture. When compressing ambient air, the non neglectable amount of vapour it contains also increases its partial pressure. Given the fact that there is a specific pressure threshold for vapour, in a unique correlation to temperature, above which it becomes saturated (in other words its dew point becomes equal to the given temperature), dew point (also called pressure dew point for compressed gases) is a direct indicator of vapour saturation in a compressed air system. Therefore, measuring pressure dew point of air in a compressed air system can help us monitor the performance of the dryer and water-traps used and warn us before vapour starts saturating and becomes harmful both for equipment and users.

Sigma offers a complete range of sensors and instruments for monitoring dewpoint, temperature and humidity that can easily fulfil your specific needs.