Function of Low Flow Cutoff and Preparation Before Setup
Low Flow Cutoff is used to force the flow output to zero when the fluid in the pipe is stationary or the flow rate is extremely low, avoiding false flow signals caused by empty pipes, bubbles, or vibration. For the Promag 53 electromagnetic flowmeter, Promass 83 Coriolis mass flowmeter, and Prosonic 93 ultrasonic flowmeter, correctly setting this parameter can significantly improve the stability of process control.
Before setup, make sure the transmitter is powered on and in measurement mode, and record the current cutoff value for restoration if needed. It is recommended to perform the setup under stable process conditions, with a full pipe and no bubbles.
General Setup Steps (Applicable to All Three Transmitters)
The following steps apply to local operation or operation via FieldCare software for the Promag 53, Promass 83, and Prosonic 93. Menu paths may vary slightly depending on the firmware version; please refer to the actual display.
- Enter the main menu and select “Setup” or “Commissioning”.
- Find “Low Flow Cutoff” under “Process Parameter”.
- Enter the required cutoff value; the unit is usually % or an engineering unit (such as m³/h, kg/h).
- Confirm and save the settings, then return to the measurement screen to observe whether the output is stable.
Note: The cutoff value should be slightly higher than the normal minimum flow, but not too high, to avoid losing real low-flow signals.
Specific Menu Paths and Parameter Recommendations for Each Model
Promag 53 Electromagnetic Flowmeter
Menu path: Main Menu → Setup → Process Parameter → Low Flow Cutoff. The cutoff value is expressed in %, based on the full scale value. A typical recommended value is 1% ~ 3%, depending on pipe diameter and medium conductivity.
Promass 83 Coriolis Mass Flowmeter
Menu path: Main Menu → Setup → Process Parameter → Low Flow Cutoff. The cutoff value is expressed in %, based on the maximum range. The recommended value is 0.5% ~ 2%; for media prone to bubbles, it can be increased appropriately.
Prosonic 93 Ultrasonic Flowmeter
Menu path: Main Menu → Setup → Process Parameter → Low Flow Cutoff. The cutoff value is expressed in %, based on full scale. The recommended value is 1% ~ 5%. Because ultrasonic measurement is sensitive to empty pipes, a higher value can be set to suppress noise.
Parameter Comparison and Setup Precautions
| Model | Menu Path | Unit | Recommended Cutoff Value |
|---|---|---|---|
| Promag 53 | Setup → Process Parameter → Low Flow Cutoff | % | 1% ~ 3% |
| Promass 83 | Setup → Process Parameter → Low Flow Cutoff | % | 0.5% ~ 2% |
| Prosonic 93 | Setup → Process Parameter → Low Flow Cutoff | % | 1% ~ 5% |
During setup, note: an excessively large cutoff value will cause loss of low-flow measurement, while an excessively small value will fail to suppress false signals. It is recommended to adjust gradually based on the process minimum flow and on-site interference conditions.
- Ensure the pipe is full to avoid cutoff triggered by an empty pipe.
- For media containing bubbles or solids, the cutoff value can be increased appropriately.
- After modification, observe for at least one complete process cycle to confirm there are no abnormalities.
Common Issues and Verification Methods
If the flow remains unstable after setup, check grounding, shielding, and medium conductivity (for electromagnetic flowmeters). For the Prosonic 93, also confirm sensor installation spacing and coupling status.
Verification method: close the valve so that flow is zero, and observe whether the output returns to zero; then slowly open the valve and confirm that flow starts to display normally above the cutoff point. If it does not meet expectations, readjust the cutoff value.