| UART: Universal Asynchronous Receiver Transmitter. |
| UDP -- (User Datagram Protocol) One of the protocols for data transfer that is part of the TCP/IP suite of protocols. UDP is a "stateless" protocol in that UDP makes no provision for acknowledgement of packets received. |
| UL: Underwriters Laboratories, Inc. An independent laboratory that establishes standards for commercial and industrial products.
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| Ultraviolet: That portion of the electromagnetic spectrum below blue light (380 nanometers).
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| Unbalance Tolerance: The unbalance tolerance with respect to a radial plane (measuring plane or correction plane) is that amount of unbalance which is specified as the maximum below which the state of unbalance is considered acceptable.
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| Unbalance: That condition which exists in a rotor when vibratory force or motion is imparted to its bearings as a result of centrifugal forces. |
| Undershoot: The difference in temperature between the temperature a process goes to, below the set point, after the cooling cycle is turned off and the set point temperature.
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| Undervoltage Protection: A circuit that inhibits the power supply when output voltage falls below a specified minimum.
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| Underwriters Laboratories Incorporated ( American association chartered to test and evaluate products, including power sources. The group has four locations so an applicant can interact with the office closest in the country to his/her own location.
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| Ungrounded Junction: A form of construction of a thermocouple probe where the hot or measuring junction is fully enclosed by and insulated from the sheath material.
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| Uninterruptible Power Supply (UPS): A type of power supply designed to support the load for specified periods when the line varies outside specified limits. UPS systems generally filter the AC line voltage and provide battery-backup power in the event that the main AC power fails. UPS systems are separated into two major categories, standby and continuous operation systems. Within each of these categories are square, quasi-square and sinewave output systems. The simplest and least expensive UPS is a standby UPS with square wave output. In a standby UPS, input power flows through the UPS (usually through a triac) to the output. If there is no filtering, the output will include noise or transients present at the input. When the input AC voltage falls below a minimum value, the input is turned off, battery power is inverted to AC and delivered to the output. The transition or switching time (from mains power to battery power) must be shorter than the power supply`s holdup time or the power supply will momentarily fail. In a continuous UPS, the DC/AC inverter is continuously supplying power to the load and the AC power serves to maintain battery charge. Of the three different types of waveforms, generating a square waveform is the easiest, least expensive and least desirable waveform. Not only does a square wave include a rich compliment of undesirable harmonics, it also charges the input energy storage capacitor of a conventional switcher (which is usually the UPS load) to a lower-than-normal peak voltage, increasing switching current, switch transistor temperature and reducing component lifetime. On the other hand, generating a sinewave output is far more difficult, expensive but more electrically desirable.
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| Union: A form of pipe fitting where two extension pipes are joined at a separable coupling.
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| Unity Coupling: The theoretical positioning of two coils so all lines of magnetic flux of one coil cut across all turns of a second coil.
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| Unix A computer operating system (the basic software running on a computer, underneath things like word processors and spreadsheets). Unix is designed to be used by many people at the same time (it is multi-user) and has TCP/IP built-in. It is the most common operating system for servers on the Internet.
Apple computers? Macintosh operating system, as of version 10, is based on Unix.
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| Unswept Volume/ Haskel gas boosters The minimum volume left in the gas section on completion of the compression stroke. This volume will normally be at system pressure when in operation. ( the min. Vol. is due to clearances, porting and check valves). |
| Unterface: The common boundary layer between two sub- stances such as water and a solid (metal); or between two fluids such as water and a gas (air); or between a liquid (water) and another liquid (oil). |
| Up Quark (u): The least massive flavour of quark, with electric charge 2/3. |
| UPS: Uninterruptible Power Supply. |
| Usable Capacity: The storage capacity in a disk array that is made available for storing user data. Usable capacity is generally the sum of the physical capacities of the array?s member disks minus the capacity required for check data and metadata. |
| UTC: Universal Time Code. |
| UUENCODE -- (Unix to Unix Encoding): A method for converting files from Binary to ASCII (text) so that they can be sent across the Internet via e-mail. |
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