Precautions for Proper Level Gauge Selection
Correct selection of a level gauge is critical to ensuring reliable performance and long service life.
Selection Based on Fluid Physical and Chemical Properties
When choosing a liquid level meter, selection should be based on the physical and chemical characteristics of the measured fluid. Key factors to consider include:
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Viscosity: High-viscosity fluids may require specialized sensing elements.
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Temperature: Ensure the level meter can operate within the fluid’s temperature range.
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Pressure: Confirm that the instrument is rated for the operating pressure.
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Corrosiveness: Select materials that can withstand chemical attack from the medium.
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Conductivity: Some level meters require conductive fluids to function properly.
Matching these properties to the appropriate meter type is essential for accurate and stable measurement.
Adaptability of Liquid Level Meters
The liquid level meter should be capable of adapting to the characteristics and flow requirements of the measured medium. This includes considerations such as pipe diameter variation, flow range, lining material, electrode material, and output current.
Reflex Gauge Glass
Precision and Accuracy Selection
Choose a level gauge with accuracy appropriate to the application. Proper accuracy selection ensures both technical suitability and cost-effectiveness.
For applications such as trade settlement, product transfer, and energy measurement, higher accuracy grades (e.g., 1.0 or 0.5) are recommended. For process control applications, accuracy should be selected according to actual control requirements.
In situations where only process flow monitoring is needed without precise control, lower accuracy grades such as 1.5, 2.5, or even 4.0 may be sufficient. In such cases, a low-cost plug-in level gauge can be selected.
Measurable Medium and Flow Rate Considerations
Instrument Range and Caliber Selection
For most general media, a full-scale flow velocity between 0.5 and 12 m/s is recommended, offering a wide measurement range and good flexibility.
The nominal diameter (caliber) of the selected instrument may differ from that of the process pipeline. It is important to verify that the actual flow velocity meets the meter’s operational requirements.
If the pipeline flow velocity is too low, reducing the instrument diameter can increase flow velocity within the measuring tube and improve measurement accuracy.
Troubleshooting and Routine Inspection
Regular inspection of the liquid level gauge is recommended. The following troubleshooting procedures apply to:
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Magnetic flap liquid level gauges
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Two-color quartz tube liquid level gauges
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Glass tube liquid level gauges
Routine checks help ensure proper operation and measurement accuracy.
Electrical Inspection and Signal Verification
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Check whether the power supply is correctly connected. If incorrect, reconnect according to the operation manual.
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Use a voltmeter to measure the voltage between +24V and O/P. The normal range should be 13V to 36V. If the voltage is abnormal, inspect the circuit or related equipment.
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After confirming normal voltage, connect a milliammeter to the 4–20 mA loop to verify output current. If the current is abnormal, replace the unit or contact customer service.
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Measure the voltage between IN and COM. The normal value should be approximately 2.5V.
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If the voltage is too low, disconnect the EXC wire.
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If the voltage returns to normal, the magnetic yellow module is faulty.
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If the voltage remains low, the signal converter may be damaged and should be replaced or inspected by customer service.
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Mechanical Issues and Corrective Measures
If the float drops to the bottom and the flag board does not return to zero, the flag board may not be able to keep up with the falling speed of the float. In such cases, a throttle device should be installed to slow down the liquid level change and ensure proper indication.
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