How to solve the problem of unstable flow meter readings in the field?

This question is...Pain points that field engineers will inevitably encounter 😅
I used "Quick troubleshooting process + solutions for common causes"In other words, following the order usually leads to catching the murderer."

First, conduct a quick 5-minute check (extremely useful).

Following this order, you don't need to remove the pipes 👇

1️⃣ Check if the pipe is full of fluid.

  • Electromagnetic/Ultrasonic:Make sure the tube is full.
  • Bubbles appear → Values jump around randomly

👉 Solution

  • Modification U-shaped tube bottom
  • Back pressure valve
  • Avoid the highest point of the pipeline

2️⃣ Are the upstream and downstream straight pipe sections sufficient?

  • Most flow meters require
    • Upstream ≥ 5–10D
    • Downstream ≥ 3–5D

👉 Solution

  • Move position
  • Or change to Anti-turbulence flow meter

3️⃣ Check grounding and shielding first
This point is often overlooked ⚡

👉 Frequently Asked Questions

  • The grounding wire was not connected.
  • Grounding both ends of the shielded cable (but it actually picks up noise).

👉 Correct method

  • Grounding resistance < 10 Ω
  • Shielded wire Single-ended grounding

4️⃣ Check if there are any "interference sources" at the scene.

  • Variable Frequency Drive (VFD)
  • large motor
  • electric welding machine

👉 Solution

  • Signal line Independent pipeline
  • Use twisted-pair shielded cable
  • Analog quantity changed to 4–20 mA

5️⃣ Is there really any flow at the scene?
Sometimes it's not a problem with the instrument panel 🤐

  • Valve vibration
  • Pump cavitation
  • The system is inherently pulsating.

👉 Solution

  • Add damping
  • Use average mode
  • Add buffer tank to pipeline

II. Targeted solutions for "unstable readings" in different flow meters

🔵 Electromagnetic flow meterLearn more about FMG electromagnetic flowmeters

Common causes:

  • The conductivity is too low
  • Electrode scale buildup
  • Bubbles/Empty Tubes

solution:

  • Confirm conductivity ≥ specification
  • Cleaning electrodes
  • Open Empty Pipe Detection
  • Add grounding ring

🟠 Ultrasonic Flow MeterLearn more about UFM ultrasonic flow meters

Common causes:

  • air bubbles or suspended matter inside the tube
  • Installation distance and angle are inaccurate.

solution:

  • Modify to multi-channel
  • Realignment
  • Avoid pump outlet

🟢 Turbine/Gear TypeLearn more about FRV turbine flow meters

Common causes:

  • Fluid pulsation
  • Large viscosity variation

solution:

  • Add damper
  • Modify Coriolis force (if high precision is required).

III. Tips and tricks commonly used by experienced workers on site 🧰

  • Unstable display does not necessarily mean unstable output (check 4–20 mA first).
  • Using "moving average" is better than adding filtering.
  • Do not run signal cables and power cables in the same cable tray.

IV. Quick Judgment in One Sentence

Unstable readings on the 90% are not due to a faulty flow meter, but rather to issues related to installation, interference, or flow conditions.

If you'd like, just tell me directly:

  • Flow meter types (electromagnetic/ultrasonic/turbine...)
  • fluid
  • Pipe diameter
  • Installation location (before/after the pump? Horizontal/vertical?)

I can directly help you "simulate catching the murderer on-site" 👷‍♂️