Prosonic 91 Low Flow Cutoff Setup Detailed Explanation
Low flow cutoff is a key function of ultrasonic flowmeters to suppress false signals under low flow rate conditions. When the fluid in the pipeline is nearly stationary, the Prosonic 91 may produce small readings due to noise or bubbles. By setting a cutoff value, these can be forced to zero. This article, based on the Prosonic 91 operation interface, explains the setup process and key points step by step.
1. Function and Principle of Low Flow Cutoff
The Prosonic 91 uses the ultrasonic transit-time method to measure flow. When the flow rate is below the cutoff threshold, the instrument automatically sets the flow output to 0. This avoids cumulative errors caused by fluid disturbance or signal noise, and is especially suitable for intermittent flow or pump start/stop scenarios.
- Eliminate false flow readings caused by微小 disturbances in the pipeline;
- Prevent cumulative volume from slowly increasing at night or during shutdown periods;
- Improve the stability of flow signals in process control.
2. Setup Steps
Enter the Prosonic 91 menu and follow these steps:
- On the main screen, press the E key to enter the main menu, then select "Setup" → "Flow" → "Cut off".
- Enter the desired cutoff value (unit consistent with the flow unit, such as m³/h or L/min).
- Press the E key to confirm and return to the main screen.
- Observe the current flow display. When the actual flow is below the cutoff value, the output should stabilize at 0.
3. Principles for Setting the Cutoff Value
The cutoff value should be determined based on the process minimum effective flow, typically recommended to be 1%~5% of full scale. Setting it too high will lose real small flows, while setting it too low will not suppress noise.
| Application Scenario | Recommended Cutoff Value (% of Full Scale) | Description |
|---|---|---|
| Clean liquid, stable flow | 1%~2% | Preserve small flow measurement |
| With bubbles or solid particles | 3%~5% | Suppress noise interference |
| Intermittent transfer, pump control | 5%~10% | Avoid false accumulation when pump stops |
4. Precautions and Verification
- After modifying the cutoff value, it is recommended to perform a zero point calibration: close the valve and confirm the flow display is 0.
- If the cutoff value is set too high, it may affect the low flow alarm function, and the alarm threshold must be adjusted accordingly.
- For bidirectional flow measurement, check the forward and reverse cutoff settings separately.
- Record parameters before and after modification for traceability and optimization.
5. Frequently Asked Questions
Q: Is it feasible to set the cutoff value to 0?
A: Yes, but the instrument may output fluctuating readings. It is recommended to set a reasonable value based on the operating conditions.
Q: After cutoff, the flowmeter still displays small flow?
A: Check for pipe vibration or sensor installation issues, and recalibrate if necessary.