GLOSSARY OF TERMS: CALIBRATION

ACCURACY: The closeness of an indication or reading of a measurement device to the actual value of the quantity being measured. Usually expressed as ± percent of full scale output or reading.

CFM: The volumetric flow rate of a liquid or gas in cubic feet per minute.

DIFFERENTIAL PRESSURE: The difference in static pressure between two identical pressure taps at the same elevation located in two different locations in a primary device.

ELECTROLYTE: Any substance which, when in solution will conduct an electric current. Acids, bases, and salts are common electrolytes.

FLOWRATE: Actual speed or velocity of fluid movement.

GPM: Volumetric flow rate in gallons per minute.

HEAD LOSS: The loss of pressure in a flow system measured using a length parameter (i.e., inches of water, inches of mercury).

HYSTERESIS: The difference in output when the measurand value is first approached with increasing and then with decreasing values. Expressed in percent of full scale during any one calibration cycle.

KELVIN: Symbol K. The unit of absolute or thermodynamic temperature scale based upon the Celsius scale with 100 units between the ice point and boiling point of water. 0 C = 273.15 K.

LINEARITY: The closeness of a calibration curve to a specified straight line. Linearity is expressed as the maximum deviation of any calibration point on a specified straight line during any one calibration cycle.

MEASURAND: A physical quantity, property, or condition which is measured.

NPT: National Pipe Thread.

POLARITY: In electricity, the quality of having two oppositely charged poles, one positive one negative.

RANGEABILITY: The ratio of the maximum flowrate to the minimum flowrate of a meter.

SENSITIVITY SHIFT: A change in slope of the calibration curve due to a change in sensitivity (i.e., minimum change in input signal to which an instrument can respond).

TRANSITIONAL FLOW: Flow between laminar and turbulent flow, usually between a pipe Reynolds number of 2000 and 4000.

VISCOSITY: The inherent resistance of a substance to flow.

ZERO ADJUSTMENT: The ability to adjust the display of a process or strain meter so that zero on the display corresponds to a non-zero signal, such as 4 mA, 10 mA, or 1 V dc. The adjustment range is normally expressed in counts.

The terms and definitions for this issue’s Word Search come from a glossary compiled by RSHydro (www.rshydro.co.uk), a UK-based consultancy that specializes in flow and level technologies.