Low Flow Cutoff Overview
Low Flow Cutoff is an important function in flowmeters used to suppress false signals at low flow or empty pipe conditions. When the fluid flow in the pipe is below the set threshold, the flowmeter forces the output to zero to avoid measurement errors caused by bubbles, vibration, or fluid disturbance. Correctly setting the low flow cutoff is essential to ensure the stability of process control and data accuracy.
This article uses Promag 53 (electromagnetic flowmeter), Promass 83 (mass flowmeter), and Prosonic 93 (ultrasonic flowmeter) as examples to introduce the general setup method for low flow cutoff.
Preparation Before Setup
Confirm Device and Parameters
- Confirm the flowmeter model and software version; menu structures may differ slightly between models.
- Obtain the minimum flow value under current working conditions; it is usually recommended to set the cutoff point to 1%–5% of full scale.
- Ensure the flowmeter is in parameter setup mode, and record the original parameters for restoration.
Access the Parameter Menu
- Enter the main menu via the local display or a commissioning tool such as FieldCare or DeviceCare.
- Select the “Setup” or “Configuration” menu.
- Find the “Low Flow Cutoff” parameter group.
Setup Steps for Each Model
Promag 53 Setup
- Go to “Setup” → “Process Parameter” → “Low Flow Cutoff”.
- Enter the cutoff value (unit consistent with the flow unit), for example 0.5 m³/h.
- Confirm and save the settings.
Promass 83 Setup
- Go to “Setup” → “Process Parameter” → “Low Flow Cutoff”.
- Set the cutoff value, usually in mass flow or volume flow units.
- You can enable the “On/Off” switch and set a hysteresis value to avoid frequent switching.
- Save the settings.
Prosonic 93 Setup
- Go to “Setup” → “Process Parameter” → “Low Flow Cutoff”.
- Enter the cutoff value; note that ultrasonic flowmeters are more sensitive to low flow, so it is recommended to increase the threshold appropriately.
- Save the settings and exit.
Parameter Comparison and Recommended Values
| Model | Default Cutoff Value | Recommended Range | Unit | Remarks |
|---|---|---|---|---|
| Promag 53 | 0.5% | 1%~3% | Percentage of full scale | Suitable for conductive liquids |
| Promass 83 | 0.2% | 0.5%~2% | Percentage of full scale | Mass flow preferred |
| Prosonic 93 | 1% | 2%~5% | Percentage of full scale | Greatly affected by bubbles |
Precautions and Common Issues
Precautions
- Setting the cutoff value too high may cause loss of low flow measurement and affect metering accuracy.
- Setting the cutoff value too low may fail to suppress noise and cause output fluctuation.
- It is recommended to use low flow cutoff together with the empty pipe detection function.
- After modifying parameters, perform a zero calibration to ensure accurate measurement.
Common Issues
- Issue: The flowmeter still outputs a small signal after setting.
Solution: Check whether the cutoff value is effective and confirm whether empty pipe detection is enabled. - Issue: The cutoff value cannot be modified.
Solution: Check whether it is in write protection status; a password may be required or the lock must be released. - Issue: The cutoff effect varies greatly with different media.
Solution: Readjust the cutoff value according to the medium characteristics, and consult the manufacturer if necessary.
Summary
Correctly setting the low flow cutoff can effectively improve the reliability of flowmeters under low flow conditions. For Promag 53, Promass 83, and Prosonic 93, the operation path is similar, but the recommended values need to be adjusted according to actual working conditions. It is recommended that engineering personnel combine empty pipe detection and zero calibration, and regularly verify the cutoff effect to ensure long-term stable operation.