When measuring oxygen flow in industrial or medical systems, accuracy and safety are top priorities. Two of the most common technologies used for oxygen measurement are the Thermal Mass Flow Meter and the Vortex Flow Meter.
Although both instruments can measure oxygen precisely, their reading methods and display information differ significantly.
In this article, you’ll learn how to read each type of oxygen flow meter correctly, understand the meaning of display data, and interpret key parameters for optimal performance.
🧠 1. How to Read a Thermal Mass Flow Meter
The thermal mass flow meter measures oxygen flow based on heat transfer from a heated sensor to the gas stream. It directly outputs mass flow or standard volumetric flow, without requiring temperature or pressure compensation.
🔹 Common Display Information
| Display Item | Meaning | Description |
|---|---|---|
| Flow / Mass Flow (kg/h or Nm³/h) | Mass or standard volume flow | Real-time oxygen flow rate. |
| Total / Totalizer | Totalized flow | Cumulative oxygen passing through the meter. |
| Temperature (°C) | Gas temperature | Used for internal compensation. |
| Velocity (m/s) | Gas velocity | Flow speed inside the pipeline. |
| Status / Alarm | Diagnostic info | Indicates over-range, sensor errors, or abnormal flow. |
🔹 Steps to Read
- Confirm Units
Ensure the display unit is Nm³/h (standard cubic meters per hour) or kg/h, depending on your setup. - Check Instantaneous Flow
Read the main display for real-time flow rate.
Example:FLOW: 35.6 Nm³/h TEMP: 26.4 °C TOTAL: 12345 Nm³→ Oxygen flow = 35.6 Nm³/h - View Total Flow (Totalizer)
Press “TOTAL” to check cumulative oxygen flow. Reset before a new measurement period if needed. - Check Alarm Status
If you see “ALARM” or “OVER RANGE,” verify oxygen pressure or check for sensor contamination.
🔹 Output Interpretation
If the device has no display:
- 4–20 mA output: corresponds to flow range (e.g. 4mA = 0, 20mA = full scale).
- RS485 / Modbus: digital communication to read flow and temperature via PLC or PC.
👉 Learn more: Thermal Mass Flow Meter for Gas Measurement
🌪️ 2. How to Read a Vortex Flow Meter
The vortex flow meter measures oxygen flow by detecting the frequency of vortices formed when gas passes around a bluff body in the pipe. The higher the vortex frequency, the higher the flow rate.
🔹 Common Display Information
| Display Item | Meaning | Description |
|---|---|---|
| Flow Rate (m³/h or Nm³/h) | Instantaneous flow rate | Oxygen flow rate under actual or standard conditions. |
| Total Flow (m³) | Totalized flow | Total volume of oxygen measured. |
| Frequency (Hz) | Vortex frequency | Proportional to flow velocity. |
| Temperature (°C) | Gas temperature | For temperature compensation. |
| Pressure (kPa or MPa) | Gas pressure | Used for standard volume correction. |
🔹 Steps to Read
- Confirm Compensation Type
- Standard vortex flow meter: displays actual volume (m³/h).
- Temperature & pressure compensated model: displays standard volume (Nm³/h).
- Read Instantaneous Flow
The first line on the screen usually shows real-time flow.
Example:Q = 12.45 Nm³/h TOTAL = 30250 Nm³→ Oxygen flow = 12.45 Nm³/h - View Total Flow
Press “MODE” or “TOTAL” to view cumulative oxygen usage. - Read Frequency Signal
The “F=XX.X Hz” reading shows vortex frequency.
Higher frequency → higher oxygen flow. - Check Alarms or Errors
“Err” or “Low Flow” indicates the flow is below the detection threshold.
🔹 For Analog (Pointer-Type) Models
Some older vortex meters use a dial display:
- Large dial = instantaneous flow (m³/h)
- Small counter = totalized flow (m³)
Read values similar to a mechanical water meter — from left to right.
👉 Related guide: Vortex Flow Meter Working Principle
⚙️ 3. Key Differences Between Thermal Mass and Vortex Flow Meters
| Feature | Thermal Mass Flow Meter | Vortex Flow Meter |
|---|---|---|
| Measured Value | Mass or standard volume flow | Actual or standard volume flow |
| Compensation Needed | ❌ Not required | ✅ Required for accuracy |
| Display Form | Digital (instantaneous + total) | Digital or pointer type |
| Output Signal | 4–20mA, RS485 | 4–20mA, Pulse |
| Accuracy | ±1% or better | ±1%–1.5% |
| Oxygen Compatibility | Excellent (clean gas only) | Good (with oxygen-cleaned design) |
✅ 4. Summary
- Thermal Mass Flow Meters: Directly show oxygen mass flow or standard volumetric flow. Easy to read, high accuracy, and no need for compensation.
- Vortex Flow Meters: Show volumetric flow based on vortex frequency; compensated models automatically convert to standard conditions.
In both cases, focus on the instantaneous flow (current value) and total flow (cumulative).
Ensure the correct units (m³/h, Nm³/h, or kg/h) and regularly verify calibration for accurate oxygen monitoring.