Why is it critical to select a pressure-based level sensor with a range that closely matches the maximum liquid depth, especially when measuring low levels?
Selecting a sensor with a measurement range that closely matches the application’s required depth is crucial for maximizing measurement resolution and accuracy. This is especially true for low-level applications. The principle is to use as much of the sensor’s analog output signal (e.g., 4-20 mA) as possible to represent the process variable.
Consider an application to measure a maximum level of 20 cm of diesel, which exerts about 17 mbar of pressure.
- Case 1: Poorly Matched Sensor. If a sensor with a range of 0-100 mbar is used, the 17 mbar of pressure only utilizes 17% of the sensor’s full-scale capability. The corresponding change in the 4-20 mA output signal would be small, making it difficult for the control system to resolve small fluctuations in level.
- Case 2: Correctly Matched Sensor. If a sensor with a range of 0-40 mbar is used, the 17 mbar of pressure utilizes about 42% of the sensor’s range. This provides a significantly larger change in the output signal for the same change in level, resulting in higher resolution and more precise process control.
Featured low range liquid level sensor products
LMP307 Submersible Level Transmitter - Submersible level transmitter for measuring liquid level with a 4-20mA current loop or a 0-10V voltage output plus optional ATEX approval for intrinsically safe use in hazardous areas in ranges from 1mH2O up to 250mH2O. The LMP307 is suitable for use on potable water with no leaching, and can be supplied with a drinking water certificate according to DVGW and KTW.
LMK457 Marine Approved Level Transmitter - Marine approved level transmitter with 4-20mA current loop output for shipbuilding with optional all CuNiFe construction for sea-water compatibility in ranges from 0.4 mH2O to 250mH2O gauge.
Furthermore, sensor accuracy is typically specified as a percentage of full-scale output (% FSO). A higher-range sensor will have a larger potential error in absolute terms. For example, a 0.5% FSO accuracy on a 100 mbar sensor is ±0.5 mbar, which is a significant error relative to a 17 mbar measurement. In contrast, a 0.35% FSO accuracy on a 40 mbar sensor is ±0.14 mbar, providing a much more accurate reading at that specific low level.
By properly matching the sensor’s range to the application, engineers can ensure higher resolution, better accuracy, and more reliable system performance.
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Related Technical Terms
- Accuracy
- BSL – Best Straight Line
- Compensated Temperature Range
- Digital Compensation
- g Effect
- Hysteresis
- LHR – Linearity, Hysteresis and Repeatability
- Long Term Stability/Drift
- NL – Non-Linearity
- PPM – Parts Per Million
- Precision
- Pressure Hysteresis
- Repeatability
- RTE – Referred Temperature Error
- Secondary Pressure Standard
- TEB – Temperature Error Band
- TEB – Total Error Band
- Temperature Compensation
- Temperature Error
- Thermal Hysteresis
- Threshold
- TSL – Terminal Straight Line
- TSS – Thermal Span or Sensitivity Shift
- TZS – Thermal Zero Shift
Related Online Tools
- Pressure Sensor Calculator
- Temperature Sensor Calculator
- Bit to Measurement Resolution Converter
- Pressure Sensing Errors Calculator
- Pressure Measurement Accuracy and Error Calculator
Related Product Types
Shallow Depth Submersible Sensor and Instrument Probes
Low Range, Shallow Depth Liquid Level Sensors
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