eBook: Automating Manufacturing Systems; with PLCs


A.12 L

label - a name associated with some point in a program to be used by branch instructions.
ladder diagram - a form of circuit diagram normally used for electrical control systems.
ladder logic - a programming language for PLCs that has been developed to look like relay diagrams from the preceding technology of relay based controls.
laminar flow - all of the particles of a fluid or gas are travelling in parallel. The complement to this is turbulent flow.
laptop - a small computer that can be used on your lap. It contains a monitor ad keyboard.
LAN (Local Area Network) - a network that is typically less than 1km in distance. Transmission rates tend to be high, and costs tend to be low.
latch - an element that can have a certain input or output lock in. In PLCs these can hold an output on after an initial pulse, such as a stop button.
LCD (Liquid Crystal Display) - a fluid between two sheets of light can be polarized to block light. These are commonly used in low power displays, but they require backlighting.
leakage current - a small amount of current that will be present when a device is off.
LED (Light Emitting Diode) - a semiconductor light that is based on a diode.
LIFO (Last In First Out) - similar to FIFO, but the last item pushed onto the stack is the first pulled off.
limit switch - a mechanical switch actuated by motion in a process.
line printer - an old printer style that prints single lines of text. Most people will be familiar with dot matrix style of line printers.
linear - describes a mathematical characteristic of a system where the differential equations are simple linear equations with coefficients.
little-endian - transmission or storage of data when the least significant byte/bit comes first.
load - In electrical system a load is an output that draws current and consumes power. In mechanical systems it is a mass, or a device that consumes power, such as a turbine.
load cell - a device for measuring large forces.
logic - 1. the ability to make decisions based on given values. 2. digital circuitry.
loop - part of a program that is executed repeatedly, or a cable that connects back to itself.
low - a logic negative, or zero.
LRC (Linear Redundancy Check) - a block check character
LSB (Least Significant Bit) - This is the bit with the smallest value in a binary number. for example if the number 10 is converted to binary the result is 1010. The most significant bit is on the left side, with a value of 8, and the least significant bit is on the right with a value of 1 - but it is not set in this example.
LSD (Least Significant Digit) - This is the least significant digit in a number, found on the right side of a number when written out. For example, in the number $1,234,567 the digit 7 is the least significant.
LSI (Large Scale Integration) - an integrated circuit that contains thousands of elements.
LVDT (Linear Variable Differential Transformer) - a device that can detect linear displacement of a central sliding core in the transformer.

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