damping coefficient is less than 1, causing the response to oscillate around the set point before settling to it. User program memory. The memory section where the application control program is stored.
Variable. A factor that can be altered, measured, and controlled. Venturi tube. A transducer that measures fluid flow by measuring the pressure differential between two points. Vertical redundancy check (VRC). An error-detecting method in which a parity bit is added to each character in a message so that the number of bits in each character, including the parity bit, is either odd or even. Vibration transducer. A device that measures the vibration of a body by measuring its displacement, velocity, or acceleration. Volatile memory. A type of memory whose contents are irretrievable after operating power is lost. VRC. See vertical redundancy check. w: Watchdog timer. A timer that monitors the logic circuits controlling a PLC. If a watchdog timer ever times out, it will disconnect the processor from the process because it will assume that the processor is faulty. Weighted value. The numerical value assigned to any single bit as a function of its position in a word. Weight input module. A special analog interface designed to read data from load cells, which convert force and weight values into electrical signals. Wire bundling. The technique of grouping an I/O module’s wires according to their characteristics (e.g., input, output, power). Wire input module. A special input interface designed to detect short-circuit or open-circuit connections between a module and its input devices. Word. The number of bits that the central processing unit operates on at one time when it is performing an instruction or operating on data. A word is usually composed of a fixed number of bits. Write. The process of putting information into a storage location. x: XOR. See exclusive-OR.
Ziegler-Nichols closed-loop tuning method. A method for determining a controller’s tuning constants by finding the value of the proportional gain that will cause the control loop to oscillate indefinitely at a constant amplitude when it is in a closed-loop system. Ziegler-Nichols open-loop tuning method. A method for determining the tuning constants for a controller by testing the process variable’s response to a change in the control variable output in an open-loop system. |
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