Glossary L

Following is a definition of terms frequently used in the instrumentation, industrial automation and test & measurement communities.

Lag: (1) A time delay between the output of a signal and the response of the instrument to which the signal is sent. (2) A time relationship between two waveforms where a fixed reference point on one wave occurs after the same point of the reference wave.

Laminar Flow: Streamlined flow of a fluid where viscous forces are more significant than inertial forces, generally below a Reynolds number of 2000.

Large Scale Integration (LSI): The combining of about 1,000 to 10,000 circuits on a single chip. Typical examples of LSI circuits are memory chips and microprocessor.

Latent Heat: Expressed in BTU per pound. The amount of heat needed (absorbed) to convert a pound of boiling water to a pound of steam.

Leakage Rate: The maximum rate at which a fluid is permitted or determined to leak through a seal. The type of fluid, the differential Limits of Error: A tolerance band for the thermal electric response of thermocouple wire expressed in degrees or percentage defined by ANSI specification MC-96.1 (1975).

Least-squares Line: The straight line for which the sum of the squares of the residuals (deviations) is minimized.

Life Cycle: The minimum number of pressure cycles the transducer can endure and still remain within a specified tolerance.

Limits of Error: A tolerance band for the thermal electric response of thermocouple wire expressed in degrees or percentage defined by ANSI specification MC-96.1 (1975).

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.

Liquid Junction Potential: The potential difference existing between a liquid-liquid boundary. The sign and size of this potential depends on the composition of the liquids and the type of junction used.

Load Impedance: The impedance presented to the output terminals of a transducer by the associated external circuitry.

Load: The electrical demand of a process expressed as power (watts), current (amps) or resistance (ohms).

Logarithmic Scale: A method of displaying data (in powers of ten) to yield maximum range while keeping resolution at the low end of the scale.

Loop Resistance: The total resistance of a thermocouple circuit caused by the resistance of the thermocouple wire. Usually used in reference to analog pyrometers which have typical loop resistance requirements of 10 ohms.

LS-TTL Compatible: For digital input circuits, a logic 1 is obtained for inputs of 2.0 to 5.5 V which can source 20 µA, and a logic 0 is obtained for inputs of 0 to 0.8 V which can sink 400 µA. For digital output signals, a logic 1 is represented by 2.4 to 5.5 V with a current source capability of at least 400 µA; and a logic 0 is represented by 0 to 0.6 V with a current sink capability of at least 16 MA. “LS” stands for low-power Schottky.

LS-TTL Unit Load: A load with LS-TTL voltage levels, which will draw 20 µA for a logic 1 and -400 µA for a logic 0.

LSD (Least-Significant Digit): The rightmost active (non-dummy) digit of the display.