If you work with HVAC controls, industrial ventilation, or process airflow monitoring, there’s a good chance you’ve run into this question:

“How do i measure air flow with a 4-20 mA output for my PLC or BMS.  How do I make these two work together?”

This article explains exactly how to take the ALMEMO FVAD15H140 digital vane airflow sensor and produce a clean, reliable 4–20 mA signal using the ALMEMO MA24901R20U analog transmitter.

What’s the Problem We’re Solving?

Most vane airflow sensors — including the FVAD15H140 — do not output a standard analog signal.
Instead, they produce a digital frequency:

• Low airflow → low frequency
• High airflow → high frequency

But 90% of PLCs, BMS controllers, and industrial inputs still rely on:

• 4–20 mA
• 0–10 V

So we need a way to convert frequency → 4–20 mA.

That’s where the MA24901R20U analog transmitter comes

The Short Answer: Yes, You Can Get 4–20 mA From a Digital Vane Sensor

And here’s exactly how you do it:

1. FVAD15H140 vane sensor outputs a frequency signal proportional to airflow.
2. The MA24901R20U transmitter accepts frequency input converts it into realworld units(m/s) and converts it to a standard 4–20 mA current loop.
3. The PLC/BMS scales 4–20 mA.

That’s the whole chain.

If you want to know more please get in touch!