# GLOSSARY OF TERMS: Level Measurement

Aug. 1, 2008

ACCURACY: The degree of conformity of a measure to a standard or a true valueCAPACITANCE: The property of a system of conductors and dielectrics that permits the storage of electricity

Accuracy: The nearness of a measured value compared to the actual value. Usually expressed as a maximum deviation from the correct value; e.g., ±1% indicates the measured value will be between 99 and 101% of the actual value.

Analog Output: A continuous electrical signal used to provide a linear representation of the level of material.

Blanking Distance: The minimum operating distance of a sensor that operates by measuring time-of-flight (e.g., ultrasonic, radar) to allow the transducer to receive an echo from the target; blanking is used to ignore strong, close reflections that are usually not the intended target.

Deadband: A region with a measurable distance but with no change in output (see hysteresis).

Differential Pressure: The variation in pressure between two separate points.

Float: Any device with a less specific gravity than the surrounding fluid thereby allowing the device to maintain buoyancy.

Hydrostatic Pressure: The pressure exerted at a known depth by a column of liquid with a consistent density.

Hysteresis: The property of an output that differs between increasing and decreasing values based on the same deadband.

Zero Offset: The divergence of a sensor’s output from the recognized zero reference point.

PSIA: Unit of pressure as pounds per square inch absolute, which places the zero reference at full vacuum; measured by the sum of gauge (see PSIG) and atmospheric pressures.

PSIG: Unit of pressure as pounds per square inch gauge, which places the zero reference at ambient atmospheric pressure.

Repeatability: The ability of a sensor to reproduce a consistent output. Usually expressed as a maximum deviation from the actual value; e.g., ±1% indicates repeatable value of between 99 and 101% of the actual value.

Resolution: The minimum change in level that a sensor is able to detect.

Response Time: The time required for an output to react to a given input.

Signal: A variation in electron flow that conveys information from one location to another.

Span: The distance or correlating output between two measureable points.

Specific Gravity (SG): A dimensionless ratio of the density of a particular material to the density of water at 4°C (39.2°F).

Submersible: Any object with the ability to operate under water.

Switch Point Output: A discrete mechanical or electronic signal that indicates a state of being opened or closed. Typically used as high or low alarm conditions.

Transducer: A device used to convert energy from one form into a different form.

This glossary of terms was contributed to Flow Control magazine by Jacob Bingham, applications engineer for Automation Products Group (www.apgsensors.com).

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