O

OBJECT LINKING AND EMBEDDING (OLE). -- A Microsoft Windows standard mechanism for embedding one program within another. For example, an Excel spreadsheet can be pasted into a Visual Basic program. If a file is linked to an OLE control, the data stored in that file is displayed in the OLE control.

OD -- Outside diameter.

Ohm -- The unit of electric resistance. The resistance value through which one volt will maintain a current of one ampere.See Ohm's Law. Ohm's Law -- Current in a circuit is directly proportional to the voltage, and inversely proportional to resistance; stated as: E = IR Where: I = Amps, I = E/R, E = Volts, R = E/I, R= Ohms The complete Ohm's Law also includes the relationships of watts to amps, volts and ohms.

ON/OFF -- A method of control that turns the output full on until set point is reached, and then off until the process error exceeds the hysteresis.

OFFSET CURRENT. -- A current that comes from a switching card even though no user signals are applied. It comes mostly from the finite coil to contact impedance. It is also generated by triboelectric, piezoelectric, and electrochemical effects present on the card.

OHMIC CONTACT. -- A resistive contact between a semiconductor material and metal. This type of contact exhibits a straight line I-V characteristic with a small value of resistance and does not significantly rectify.

OPERATING SYSTEM. -- Base-level software that organizes the computer's resources and capabilities, runs application programs, interacts with users, and communicates with installed and peripheral devices. Popular operating systems include DOS, Windows, OS/2, and UNIX.

OVERLOAD PROTECTION. -- A circuit that protects the instrument against excessive current at the input terminals.

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P

P-TYPE. -- The conductivity type of a semiconductor material when the majority of carriers are holes, hence positive. P-type silicon is doped with dopant atoms from column III of the periodic table, such as boron.

PANEL LOCK -- A feature that prevents operation of the front panel.

PARALLEL CIRCUIT -- A circuit configuration in which the same voltage is applied to all components, with current divided among the components according to their respective resistances or impedance's.

PARAMETER-- A value that determines the response of an electronic controller to given inputs.

PARTS PER MILLION (PPM). -- Represents the concentration of gases or vapor in air. For example, 1 ppm means that 1 unit of the gas is present for every 1 million units of air..

PC. -- Abbreviation for Personal Computer.

PCI. -- Abbreviation for Peripheral Component Interconnect. It is a standard for a local bus.

PCMCIA. -- Abbreviation for Personal Computer Memory Card International Association. This organization establishes standards for portable computers.

PEAK RESPONDING. -- A measurement where the displayed value is equal to the peak value of the input signal.

PER CHANNEL RATE. -- The sample rate for each channel of a scanning A/D system.

PN JUNCTION. -- The interface between n-type and p-type semiconductor material. This structure forms a pn junction diode.

POLARITY-- The electrical quality of having two opposite poles, one positive and one negative. Polarity determines the direction in which a current tends to flow.

POLE. -- A combination of mating relay contacts: normally open, normally closed, or both.

PROGRAMMED I/O. -- A standard method of accessing an I/O device - the CPU reads each byte of data from or writes each byte of data to the device.

PYROPHORIC. -- A chemical that will ignite spontaneously in air at a temperature less than or equal to 54.4¡C (130¡F).

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Q

QUANTIZATION. -- A process where the continuous range of values of an input signal is divided into non-overlapping sub-ranges and, to each sub-range, a discrete value of the output is uniquely assigned.

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R

RADIATION -- Radiant energy emitted in the form of waves or particles. See emissivity and infrared.

Radio Frequency Interference (RFI) Electromagnetic waves.between the frequencies of 10 KHz and 300 GHz that can affect susceptible systems by conduction through sensor or power input lines, and by radiation through space.

RAMP -- A programmed increase in the temperature of a set point system.

RANGE -- The area between two limits in which a quantity or value is measured. It is usually described in terms of lower and upper limits.

RATED ACCURACY. -- The limit that errors will not exceed when the instrument is used under specified operating conditions. It is expressed as a percentage (of input or output) plus a number of counts.

READING.-- The displayed number that is proportional to the measured magnitude of the input signal.

READING RATE. -- The rate at which the displayed number is updated.

RELIABILITY. -- The ability of a device to perform within the desired range over a measured period of time.

REPEATABILITY.-- The ability of an instrument to measure the same input to the same value over a short period of time and over a narrow temperature range.

RESISTANCE -- Opposition to the flow of electric current,measured in ohms. See ohms.

RESISTANCE TEMPERATURE -- Characteristic The characteristic change in a sensor's resistance when exposed to a change in temperature. See positive temperature coefficient and negative temperature coefficient.

Resistance Temperature Detector (RTD) -- A sensor that uses the resistance temperature characteristic to measure temperature. There are two basic types of RTDs: the wire RTD, which is usually made of platinum, and the thermistor, which is made of a semiconductor material. The wire RTD is a positive temperature coefficient sensor only, while the thermistor can have either a negative or positive temperature coefficient.

RESISTANCE INSERTION. -- A current measuring technique where a known resistor is connected in series with the circuit to be measured. The voltage drop across the resistor is proportional to the unknown current.

RESISTIVITY. -- The geometry independent parameter of a material that determines the relationship between the current through it and the current across it. Resistance of a cylinder of material is: resistance = resistivity * (length / area)

RESOLUTION. -- The smallest value of input (or output) signal,other than zero, that can be measured (or sourced) and displayed. Also called sensitivity or minimum resolvable quantity.

RESOLUTION (DATA ACQUISITION). -- The smallest signal increment that can be detected by a measurement system. It is usually specified in "bits."

RESPONSE TIME. -- For a measuring instrument, the time between application of a step input signal and the indication of its magnitude within a rated accuracy. For a sourcing instrument, the time between a programmed change and the availability of the value at its output terminals. Also known as Settling Time.

RISE TIME. -- The time required for a signal to change from a small percentage (usually 10%) to a large percentage (usually 90%) of its peak-to-peak amplitude. See also FALL TIME.

RMS RESPONDING. -- A measurement where the displayed value is equal to the root-mean-square (rms) of the input signal, for all input waveforms having components within the specified frequency range and crest factor limit.

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S

SAE -- See Society of Automotive Engineers.

SAMPLE. -- A value that is read from or written to one channel.

SAMPLE RATE. -- The rate at which a continuous-time signal is sampled. It is frequently expressed as samples/sec (S/s), kilosamples/sec (kS/s), or Megasamples/sec (MS/s).

SCHOTTKY DIODE. -- A junction or barrier formed by the direct contact of semiconductor materials with a metal. This type of contact rectifies signals and may also exhibit some resistance.

SEEBECK COEFFICIENT -- The rate of change (derivative) of thermal EMF (voltage) with respect to temperature. Expressed as millivolts per degree.

SEEBECK EFFECT -- When a circuit is formed with a junction of two dissimilar metals and the junctions at each end are held at different temperatures, a current will flow in the circuit.

SEEBECK EMF -- The net thermal electromotive force (EMF) in a thermocouple under conditions of zero current.

SEMICONDUCTOR -- Any material that exhibits a degree of electrical conductivity that falls between that of conductors and dielectrics.

SERIAL COMMUNICATION -- A method of transmitting information between devices by sending all bits serially over a single communication channel.

• EIA/TIA-232 (formerly RS-232) -- An Electronics Industries of America (EIA)/Telecommunication Industry Association (TIA) standard for interface between data terminal equipment and data communications equipment for serial binary data interchange. This is usually for communications over a short distance (50 feet or less) and to a single device.
• EIA/TIA-485 (formerly RS-485) -- An Electronics Industries of America (EIA)/Telecommunication Industry Association (TIA) standard for electrical characteristics of generators and receivers for use in balanced digital multipoint systems. This is usually used to communicate with multiple devices over a common cable or where distances over 50 feet are required.

SERIES CIRCUIT -- A circuit configuration in which a single current path is arranged among all components.

SEMICONDUCTOR. -- An element such as silicon or germanium or a compound like GaAs that has an intermediate band gap. Unlike metals that freely conduct and insulators that do not conduct charge, semiconductors selectively conduct charge through the movement of holes and electrons.

SETTLING TIME. -- For a measuring instrument, the time between application of a step input signal and the indication of its magnitude within a rated accuracy. For a sourcing instrument, the time between a programmed change and the availability of the value at its output terminals. For a switching card, the time required for establishing relay connections and stabilizing user circuits. Also known as Response Time.

SETTLING TIME (DATA ACQUISITION) -- Time it takes for a voltage to settle and remain within a specified error band around the final value.

SHIELDING. -- A metal enclosure for the circuit being measured or a metal sleeve surrounding wire conductors (coax or triax cable) to lessen interference, interaction, or current leakage. The shield is usually grounded.

SHUNT-- In an electrical circuit, a low resistance connection between two points that forms an alternate path for some of the current. Dielectric materials lose resistance at temperatures above their operating range. This condition can cause shunting of the sensor's signal, causing an error in the reading.

SIGNAL -- Any electrical transmittance that conveys information.

SILICON -- A tetravalend nonmetallic element.

Silicon Controlled Rectifier (SCR) -- A solid state device, or thyristor, with no moving parts, that is used in pairs to control AC voltages within one cycle. SCRs control voltage from a power source to the load by burst firing (also called zero-cross firing) or phase-angle firing. See burst fire.

SIGNAL/NOISE RATIO. -- The ratio of the maximum signal that can be measured to the level detected with no signal present (noise level). It is expressed in decibels.

SILICON.-- The most common elemental semiconductor. From silicon crystals that are grown and sliced into wafers.

SIMULTANEOUS SAMPLE-AND-HOLD.-- Operation in which the analog input channels are sampled at the same time and the values held until sequentially read by a scanning A/D system.

SINGLE-ENDED. -- The condition where the low terminal of a two-terminal instrument is connected to a specific reference point, such as power line common, earth ground, or circuit common.

SINGLE-ENDED INPUT (DATA ACQUISITION). -- An analog input with one input terminal whose value is measured with respect to a common ground. See also DIFFERENTIAL INPUTS.

SLAVE. A mainframe that is externally connected to a controlling mainframe (master). A slave unit adds capacity or functions to the master. See also MASTER and MAINFRAME.

SLEW RATE.-- The maximum charge rate of the signal sampling capacitor in the sample and hold circuit of an A/D converter. It is expressed in volts/microsecond.

SOFTWARE TRIGGER. -- A programmed event that starts an operation such as data acquisition.

SOLID STATE -- A device that can control current without.moving parts, heated filaments, or vacuum gaps; transistors, germanium diodes, and thermistors are all solid state devices.

Solid State Relay (SSR) -- See relay, solid state. Span The difference between the lower and upper limits of arange expressed in the same units as the range. See range.

SOURCE IMPEDANCE. -- The combination of resistance and reactance that a source presents to the input terminals of a measuring instrument.

STAIRCASE WAVEFORM. -- A waveform in which the voltage is incremented in uniform steps from the start voltage to the stop voltage.

STANDARD -- A set value or reference point from which measurements or calibrations are made.

SUBLIMATION -- The change of state in matter from solid to gas.

SURGE CURRENT -- A short duration rush of current that occurs when power is first applied to capacitive, inductive, or temperature dependent resistive loads, such as tungsten or silicon carbide heating elements. It also occurs when inductive loads are de-energized. Surge currents usually last no more than several cycles.

SUBROUTINE. -- A set of software instructions executed by a single line of code.

SUBSTRATE. -- The underlying material upon which a device circuit or epitaxial layer is fabricated. This term also applies to the MIS capacitor, which has only two terminals: the gate and substrate.

Systeme Internationale (SI) -- The system of standard metric units.

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T

TCR -- Temperature Coefficient of Resistance is the average resistance change/degree over the range of 0 to 100¼C. By knowing the TCR a customer can convert a resistance (ohm) value to temperature.

TEMPERATURE, AMBIENT -- The temperature of the air or other medium that surrounds the components of a thermal system.

TEMPERATURE CALIBRATION POINT -- A temperature at which the output of a sensor is compared against a standard.

TEMPERATURE COEFFICIENT.-- A change in reading (or sourced value) with a change in temperature. It is expressed as a percentage of reading (or sourced value), plus a number of counts per degree change in temperature.

TEMPERATURE COEFFICIENT OF RESISTANCE. -- The amount of resistance change of a material per degree of temperature change.

THERMOCOUPLE (T/C) A temperature sensing device made by joining two dissimilar metals. This junction produces an electrical voltage in proportion to the difference in temperature between the hot junction (sensing junction) and the leadwire connection to the instrument (cold junction).

THERMOCOUPLE TYPE -- A particular combination of metallic elements and/or alloys that make up the conductors of a thermocouple, and defines their EMF output relative to absolute temperature. ANSI designated types include: B, E, J, K, N, R, S and T.

Non-ANSI types include: C, D and G (tungsten based thermocouples) and Pt 2.

THERMOELECTRIC VOLTAGE. -- Voltages resulting from temperature differences within a measuring circuit or when conductors of dissimilar materials are joined together. Also known as thermal EMF or thermal offset. See CONTACT POTENTIAL.

THIN FILM. -- A thin layer of material grown or deposited on a substrate.Typically, layer thickness is measured in tens to thousands of angstroms for insulators and microns for metals.

THRESHOLD VOLTAGE (VT). -- The gate voltage needed to turn on a MOS enhancement-mode device.

THROUGHPUT. -- The maximum rate at which a data conversion system can perform repetitive conversions within a specified accuracy. It is determined by summing the various times required for each part of the conversion system and then taking the inverse of this time. The throughput rate takes into account the total time required to process a signal and store the value in either on-board or system memory.

TIMEBASE ACCURACY. -- A measure of how closely the internal timebase of an instrument tracks a known time standard.

TIMING JITTER.-- The short-term variation of the time period between sample points.

TOTAL HARMONIC DISTORTION.-- The percentage of harmonic distortion present in an output signal over a specified frequency range.

TRANSCONDUCTANCE. -- The ratio of the incremental change in the output current of any amplifying circuit or device to the incremental change of input voltage causing it, when the output voltage is held constant.

TRANSFER RATE. -- The rate at which data is transferred to or from memory.

TRANSISTOR. -- A semiconductor device in which a small control signal is used to control a larger current flow.

TRIGGER (INSTRUMENTATION). -- An external stimulus that initiates one or more instrument functions. Trigger stimuli include: an input signal, the front panel, an external trigger pulse, and IEEE-488 bus X, Talk, and GET triggers.

TRIGGER (DATA ACQUISITION). -- An event that starts or stops an operation. A trigger can be a specific analog, digital, or software condition. See also ANALOG TRIGGER and DIGITAL TRIGGER.

TRIGGER CONDITIONS. -- Refers to trigger sensitivity, polarity, etc.

TRIGGER HYSTERESIS. -- Applies only to analog triggers. It helps prevent noise from triggering an operation or event. For a positive-edge trigger, the analog signal must be above the specified voltage level by at least the amount of the hysteresis value before the trigger occurs. For a negative-edge trigger, the analog signal must be below the specified voltage level by at least the amount of the hysteresis value before the trigger can occur.

TRIGGER LATENCY. -- The fixed time offset between the trigger event and the first sample point.

TRIGGER MODE.-- Refers to when data acquisition begins and ends in relationship to the trigger. Trigger modes include normal-trigger, pre-trigger, about-trigger, post-trigger, trigger-to-trigger, and trigger-to-about-trigger.

TRIGGER POLARITY. -- For edge-sensitive triggers: trigger polarity defines whether the trigger occurs when the signal is rising (positive direction) or falling (negative direction). For level-sensitive triggers: trigger polarity defines whether the trigger occurs when the signal is above a level (positive) or below a level (negative).

TRIGGER SENSITIVITY. -- Refers to edge and/or level of a trigger. For analog triggers, trigger sensitivity defines whether the trigger occurs on a transition across a specified value (edge) or whether the trigger occurs when it is above or below a specified value (level). For digital triggers, trigger sensitivity defines whether the trigger occurs on a transition from one state to another state (edge) or whether the trigger occurs when it is at a specified value (level).

TTL. -- Abbreviation for transistor-transistor-logic. A popular logic circuit family that uses multiple-emitter transistors. A low signal state is defined as a signal 0.8V and below. A high signal state is defined as a signal +2.0V and above.

TWISTED PAIR -- Two insulated conductors that are twisted together. An effective method of duplexing and reducing electromagnetic interference (EMI).

TWO-TERMINAL RESISTANCE MEASUREMENT. -- A measurement where the same current flows through the unknown and the test leads.

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U

UL¨ -- The registered trademark and abbreviation for the Underwriters Laboratories, Inc. An independent testing laboratory that establishes commercial and industrial standards, and tests and certifies products in the United States.

ULTRAVIOLET -- The portion of the electromagnetic spectrum that is just beyond the violet in the visible spectrum. Ultraviolet light can degrade many insulation materials.

UNDERSHOOT -- The amount by which a process variable falls below the set point before it stabilizes.

UNIPOLAR. An analog signal range that is always positive (through zero.)

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V

VAC/VDC -- Volts alternating current, volts direct current.

VDE -- Abbreviation for Verband Deutscher Elektrotechniler, an independent German testing and certification institute concerned with the safety of electrical products. Authorizes use of the VDE Mark.

VISCOSITY -- The resistance of fluid to sheering forces (flow). High viscosity indicates a tendency for a fluid to flow or move slowly. The viscosity of fluids decreases as their temperatures increase. Heating gases will increase their absolute viscosity.

Volt (V) -- The unit of measure for electrical potential, voltage or electromotive force (EMF). See voltage.

Volt Amperes (VA) -- A measurement of apparent power. The product of voltage and current in a reactive circuit.V (voltage) áI (current) = VA. The term watt is used for real power.

Voltage (V) -- The difference in electrical potential between two points in a circuit. It's the push or pressure behind current flow through a circuit. One volt (V) is the difference in potential required to move one coulomb of charge between two points in a circuit, consuming one joule of energy. In other words, one volt (V) is equal to one ampere of current (I) flowing through one ohm of resistance (R), or V = IR.

VALENCE BAND. -- The energy levels of the electrons in he outermost shell of the atoms making up a solid material.

VAPOR. -- A gaseous form of a material that is normally a solid or liquid at room temperature and pressure.

VAPOR DENSITY. -- The density of a vapor compared to the density of an equal amount of air.

VARIABLE FREQUENCY. -- Frequency settable over a range. This term is applied to a capacitance meter that offers a choice of test signal frequencies from so many that it is essentially continuously adjustable.

VOLTAGE BURDEN. -- The voltage drop across the resistor for the resistance insertion technique of current measurement.

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W

WARM-UP TIME.-- The time required after power is applied to an instrument to achieve rated accuracy at referenced conditions.

Watt (W) -- A measurement of real power. The product of voltage and current in a resistive circuit. V (voltage) áI (current) = P (power in watts).

WORD. -- The standard number of bits that a processor manipulates at one time. Microprocessors typically use 16-, or 32-bit words. (Or 2 bytes and 4 bytes respectively.)

WORK FUNCTION. -- The minimum energy required to remove an electron from the Fermi level of a material into field-free space. Work function is normally expressed in electron volts.

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Y

YIELD. -- The ratio of good units obtained divided by the total units produced. It is the percent of wafers, dice, or packaged units conforming to specifications.

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Z

ZERO OFFSET. -- The reading (desired or undesired) that occurs when the input terminals of a measuring instrument are shorted.

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