## 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.