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Windmill - Data Acquisition and Control Glossary
Category: Technical and IT > Data Acquisition
Date & country: 18/09/2007,
Words: 222


Transient
A short surge of current or voltage, often occurring before steady-state conditions have become established.

Trigger
A trigger is something that causes a data acquisition system to start collecting data. It may be as simple as pressing a software button or a set of conditions which when met trigger data capture (internal triggers), or an externally generated, hardware signal (an external trigger). For more information see Issue 45 of the Monitor newsletter.

Truncation
Rejection of the final digits in a number, thus lessening the precision but not necessarily the accuracy.

TTL
Abbreviation for transistor-transistor logic. Referring to logic circuits consisting of two or more directly interconnected transistors, to provide conditional switching capability.

TTL-Compatible
For digital input circuits, a logic 1 is obtained for inputs of 2.0 to 5.5 V which can source 40 microA, and a logic 0 for inputs of 0 to 0.8 V which can sink 1.6 mA. 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 microA; and a logic 0 by 0 to 0.6 V with a current sink capability of at least 16 mA.

Twisted Pair
Cable that consists of individual wires wrapped around each other for carrying telephone or computer data. Reduces pickup noise levels in signals.

UART
Universal Asynchronous Receiver/Transmitter. In serial communications, the UART takes bytes of data and transmits the individual bits sequentially. Adds Start, Stop and sometimes Parity bits before and after the transmitted word.

Unipolar
A signal range that is always positive or always negative, for example 0 to +10 V.

UPS
Uninterruptible Power Supply. Used to keep critical equipment, including computers, running in the event of a mains power failure.

USB
Universal Serial Bus A serial bus gradually replacing RS232 on PCs because of its higher speed. Generally fitted as standard in new PCs.

VAC
AC Voltage

Velocity
The rate of change of displacement; dx/dt.

Volt
SI unit of potential difference such that the potential difference across a conductor is 1 volt when 1 ampere of current in it dissipates 1 watt of power. Named after Count Alessandro Volta (1745-1827). Symbol V.

Voltage
The value of an electromotive force or potential difference expressed in volts.

Voltage-to-Frequency Converter
A device that converts an analogue input voltage into a sequence of digital pulses with a frequency that is proportional to the input voltage.

WAN
Wide area network. A network of circuits spanning a large region which is used to transmit data.

Wheatstone Bridge
A network of four resistances, an emf (voltage) source, and an indicator connected such that when the four resistances are matched, the indicator will show a zero deflection or 'null' reading. Prototype of most other bridge circuits.

Wi-Fi
Wireless Fidelity. A wireless communications network conforming to IEEE 802.11 specifications. More details of Wi-Fi are in issue 82 of Monitor

x-axis
Conventionally, the horizontal axis of any type of graph.

y-axis
Conventionally, the axis perpendicular to and in the horizontal plane through the x-axis of any type of graph.

z-axis
Conventionally, the vertical axis in any three-dimensional co-ordinate system.

Zero Balance
With transducers like strain gauges, the output is large compared to the changes caused by the strain. Setting a zero balance subtracts an offset (actually a fraction of the bridge excitation voltage), so the changes caused by the strain can be accurately measured.