- SD flow meters
- Technology
SD flowmeters use thermal technology
SD flow meters combine integrated temperature and pressure sensors with air flow sensors to monitor compressed air and specialty gases. Using IO-Link technology adds benefits including real-time analytics.
Thermal flow sensing technology relies on the cooling effect of flowing fluids, including gases. For the SD design, one ceramic probe is heated (the measuring resistor) and the other is not (reference resistor). Flow velocity is determined by the voltage difference between the two resistors when the flow dissipates the heat.
Product testing
We at ifm want you to trust our measuring systems just as we have done for the last 50 years. Therefore we test all of our sensors for their technical properties and their resistance to external influences. In our test laboratory, we test not only our own sensor technology but also that of our market competitors. The following details some of our test results.
Response time
The step response time describes the time required by an instrument to measure a change in flow velocity. The faster the flow change is detected, the more precise the totalizer counter is and the faster your control system can react to changing conditions. We tested the response time for both rising flow rate (0...44 Nm3/hr) and falling flow rate (44...0 Nm3/hr). Not only does the ifm SD air flow meter have the fastest response time, it also has the most consistent response time for both rising and falling flow. This means consistency regardless of process changes.
Standard flow rates vs. actual flow rates (SCFM vs. ACFM)
Unlike many liquid media, gases are compressible media. Compressible means that gases change their volume under pressure.
In order to still obtain comparable flow rate measurements at varying levels of pressure, the volume must correspond to a defined state known as “standard conditions”.
Standard DIN ISO 2533 defines the standard conditions of gases as:
Pressure: 1013 mbar (1.013 bar)
Temperature: 15°C
Relative humidity: 0%
Why is this important? Example: Compressed gas cylinder
What does the sensor measure?
If the cylinder in our example is filled with compressed air and the quantity is measured using the SD compressed air meter, the sensor measures 100 standard liters if filled at 10.13 bar. Accordingly, the sensor always converts the volumetric flow quantity to the “standard conditions”. This compensates for both pressure and temperature changes and the sensor accurately measures the quantity of air consumed.