Glossary

NI Switches

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Glossary

Prefixes

Symbol	Prefix	Value
p	pico	10 ^-12
n	nano	10 ^-9
µ	micro	10 ^-6
m	milli	10 ^-3
k	kilo	10 ³
M	mega	10 ⁶
G	giga	10 ⁹
T	tera	10 ¹²

Numbers/Symbols

nV	nanovolts	10^-9 volts
µV	microvolts	10^-6 volts
µΩ	microohms	10^-6 ohms
mΩ	milliohms	10^-3 ohms
MΩ	megaohms	10⁶ ohms
pA	picoamps	10^-12 amperes
nA	nanoamps	10^-9 amperes
µA	microamps	10^-6 amperes
mA	milliamps	10^-3 amperes

A
A	amps
AC	alternating current
AC current	The measurement of the electrical current (in amperes) of AC signals. The measurement is typically made using rms averaging.
AC Voltage	A voltage that changes as a function of time.
ADE	application development environment—A software environment incorporating the development, debug, and analysis tools for software development. LabVIEW, Measurement Studio, and Visual Studio are examples.
American Wire Gauge	AWG—A U.S. standard set of non-ferrous wire conductor sizes. Gauge means the diameter. Non-ferrous includes copper and also aluminum and other materials, but is most frequently applied to copper household electrical wiring and telephone wiring. Typical household wiring is AWG number 12 or 14. Telephone wire is usually 22, 24, or 26. The higher the gauge number, the smaller the diameter and the thinner the wire. Since thicker wire carries more current because it has less electrical resistance over a given length, thicker wire is better for longer distances. For this reason, where extended distance is critical, a company installing a network might prefer telephone wire with the lower-gauge, thicker wire of AWG 24 to AWG 26. AWG is sometimes known as Brown and Sharpe (B&S) Wire Gauge.
analog	A signal whose amplitude can have a continuous range of values.
API, application programming interface	A standardized set of subroutines or functions along with the parameters that a program can call. A set of functions exported by a library.
B
bandwidth	The range of frequencies present in a signal, or the range of frequencies to which a measuring device can respond.
Break-Before-Make	A type of switching contact that is completely disengaged from one terminal before it connects with another terminal.
bus, buses	The group of electrical conductors that interconnect individual circuitry in a computer. Typically, a bus is the expansion vehicle to which I/O or other devices are connected. Examples of PC buses are the PCI, AT(ISA), and EISA bus.
C
capacitance	The ability to hold an electrical charge.
CH	channel
channel	Pathway from a CPU or, on a network, between computers. A channel can also be an input connection to a data acquisition system or to an instrument, such as an oscilloscope or logic analyzer. Pin or wire lead to which you apply or from which you read an analog or digital signal. Analog signals can be single-ended or differential. For digital signals, channels group to form ports. Ports usually consist of either four or eight digital channels.
characteristic impedance	A transmission line parameter that determines how propagating signals are transmitted or reflected in the line.
CMOS	Complementary-Metal-Oxide Semiconductor
cold junction, cold-junction, cold-junction compensation	A method of compensating for inaccuracies in thermocouple circuits. An artificial reference level that compensates for ambient temperature variations in thermocouple measurement circuits. IC temperature sensors are linear and their output is expressed as mV/°C. A 10 mV/°C sensor, for example, outputs 250 mV at 25 °C. Thermistor outputs, however, are nonlinear. Therefore, thermistor output is specified as the voltage range over a defined temperature range (x volts at 50 °C to y volts at 0 °C).
cold switching	The process of closing the relay contacts before applying voltage and current, as well as removing voltage and current before opening the contacts.
COM	The common terminal of a multiplexer.
contact bounce	The intermittent and usually undesired opening of mechanical relay contacts during closure, or closing of contacts during opening. The contact bounce period depends upon the type of relay and varies from .5 ms for small reed relays to 10-20 ms for larger relays.
contact life	The maximum number of expected switch or relay closures with a given voltage/current load before failure.
contact material	The material of which the contacts of a relay are made.
contact potential	A voltage produced between contact terminals due to the temperature gradient across the relay contacts.
contact rating	The maximum voltage, current, and power capacities of relay contacts under specified environmental conditions.
contact resistance	The electrical resistance across closed contacts.
contactor	An electric switch for controlling a motor or other electric device.
Controller	An intelligent device (usually involving a CPU) that is capable of controlling other devices.
crosspoint switch	An integrated circuit term; a switch that connects the signal on an input bus to one or more output buses. Also referred to as a switch matrix.
current	The rate of flow of electric charge measured in amperes.
current drive	The ability to supply a given output current. Refer to current sinking.
current drive capability	The amount of current a digital or analog output channel is capable of sourcing or sinking while still operating within voltage range specifications.
current excitation	The channel of a DMM that emits a current across a resistor in a 4-wire measurement.
current loop	A communications method that transmits data as current flow over relatively long distances and through environments with relatively high noise.
current sinking	The ability of a signal generator or output of a DAQ device to dissipate current for analog or digital output signals. Refer to current drive.
current sourcing	The ability of a DAQ device or instrument device to supply current for external devices, such as sensors or conditioning units. ICP is one technique for supplying DC current to transducers with built-in amplifiers.
D
DAQ	Data acquisition—The process of collecting and measuring electrical signals from sensors, transducers, and test probes or fixtures and inputting them to a computer for processing. Data acquisition—The process of collecting and measuring the same kinds of electrical signals with A/D and/or DIO devices plugged into a computer, and possibly generating control signals with D/A and/or DIO devices in the same computer.
dB	decibel
DC	direct current—Although the term speaks of current, many different types of DC measurements are made, including DC voltage, DC current, and DC power.
DC coupled	Allowing the transmission of both AC and DC signals.
DC current	The electric current of a DC signal.
DC gain error	The gain error on the DC component of a signal. This specification is not applicable when the device has AC input coupling.
DC offset	The DC voltage or current present on a signal. A typical technique in many instruments is to put the instrument in DC offset calibration mode, where the external signal is removed. Then, the internally generated DC offset signal is measured, and in some cases, stored, and compensated for.
DC voltage	The direct current (non-changing) component of a voltage. In practice, the DC voltage should not change over the period of observation, that is, the measurement time.
dielectric constant	The ratio of a capacitance using a given dielectric to the capacitance using a vacuum as a dielectric.
differential thermal EMF	the voltage difference between two junctions
DMM	digital multimeter—A digital instrument capable of measuring several different fundamental electrical characteristics, most often voltage, resistance, and current.
DPDT	double-pole double-throw
drive current	the current that flows through the coil of an electromechanical relay to move the armature
dry circuit switching	Switching below specified levels of voltage and current to minimize any physical and electrical changes in the contact junction.
dry reed relay	A glass enclosed, hermetically sealed, magnetically actuated contact. Typical atmosphere inside the glass enclosure is nitrogen.
E
E Series	A standard architecture for instrumentation-class, multichannel data acquisition devices.
electrical life	The number of switch cycles, under load, before the contact resistance of a relay rises above 1 Ω.
electromechanical relay	A type of relay composed of a coil, an armature mechanism, and contacts.
EMF	electromotive force—The electrical force present without a load on the circuit.
F
FET switch	Field-Effect Transistor—A type of relay composed of several CMOS transistors. A voltage applied to the control circuitry connects the source and drain of a transistor network.
form	A classification of relays categorized by the number of poles, throws, and default position of the relay.
frequency	The basic unit of rate, measured in events or oscillations per second using a frequency counter or spectrum analyzer. Frequency is the reciprocal of the period of a signal.
front panel	The interactive user interface of a VI. Modeled after the front panel of physical instruments, it is composed of switches, slides, meters, graphs, charts, gauges, LEDs, and other controls and indicators. The physical front panel of an instrument or other hardware
Functions palette	The LabVIEW palette containing block diagram structures, constants, communication features, and VIs.
fundamental	The component of a periodic wave whose frequency, f0, is the greatest common divisor of the harmonic frequencies, and the inverse of the wave period T.
G
general-purpose topology	A topology composed of multiple isolated relays used to connect one input to one output.
ground	A pin. An electrically neutral wire that has the same potential as the surrounding earth. Normally, a noncurrent-carrying circuit intended for safety. A common reference point for an electrical system.
H
handshaking	A type of scanning similar to synchronous scanning except that the switch sends a digital pulse back to the other device after each scan list entry has been executed.
harmonic	Pertaining to whole-number multiples of the fundamental frequency of a sound or signal.
HVAB	high-voltage analog bus
I
impedance	The electrical characteristic of a circuit expressed in ohms and/or capacitance/inductance. resistance
inductance	The characteristic of a coil that generates a voltage due to changes in the current. An inductor creates a voltage that is the derivate of the current, while a capacitor creates a voltage that is the integral of the current.
insertion loss	The attenuation of signals due to the impedance when passing the signals through a switching module or system. Specified as a decibel value (dB) over a frequency range.
isolation voltage	The voltage that an isolated circuit can normally withstand, usually specified from input to input and/or from any input to the amplifier output, or to the computer bus.
L
LabVIEW	Laboratory Virtual Instrument Engineering Workbench—A program development application based on the programming language G and used commonly for test and measurement purposes.
latching	The ability to keep a relay contact in its current state if power is removed.
latching relay	A type of electromechanical relay without a default position that remains in its last position when the drive current stops flowing.
LED	light-emitting diode
load impedance	Resistance, capacitance, and (often) inductance presented by a load to an output amplifier. The recommended load impedance is the minimum resistance and maximum capacitance that the circuitry connected to the analog output should have.
load regulation	The ability of a power supply to keep its output voltage or current at a constant value with a changing output load.
M
make-before-break	Breaking and completing two paths simultaneously.
matrix	A topology in which you can connect multiple inputs to multiple outputs organized as columns and rows.
MAX	Measurement & Automation Explorer—A controlled, centralized configuration environment that allows you to configure all of your NI devices.
Measurement Category	The following is a description of measurement categories: Measurement Category I is for measurements performed on circuits not directly connected to MAINS 1 . This category includes signals such as voltages on a printed wire board (PWB) on the secondary of an isolation transformer. Measurement Category II is for measurements performed on circuits directly connected to the low-voltage installation. This category refers to local-level distribution such as that provided by a standard wall outlet. Measurement Category III is for measurements performed in the building installation. This category is a distribution level referring to hardwired equipment that does not rely on standard building insulation. Measurement Category IV is for measurements performed at the source of the low-voltage (<1,000 V) installation.
mechanical life	The number of switch cycles before the contact resistance of a relay rises above 1 Ω.
MOSFET	Metal-Oxide-Semiconductor Field-Effect Transistor
mux	synonym for multiplexer
multiplex	To assign more than one signal to a channel.
multiplexer	A topology in which you can connect one input to multiple outputs or one output to multiple inputs.
N
NC	normally closed
NO	normally open
nonlatching relay	A type of electromechanical relay with an initial position of normally closed maintained by the force of a spring or permanent magnet while no drive current flows.
P
path	The route a signal follows through the switch from input terminal to output terminal.
path resistance	The resistance of a complete signal path from source to destination. This includes resistance of wiring, switching, and input and output connectors.
PCB	printed circuit board
PXI	PCI eXtensions for Instrumentation—A modular, computer-based instrumentation platform.
PXI Express	PCI Express eXtensions for Instrumentation—The PXI implementation of PCI Express, a scalable full-simplex serial bus standard that operates at 2.5 Gbps and offers both asynchronous and isochronous data transfers.
PXI Express-compatible module	A modified PXI module that is compatible with existing PXI chassis slots and PXI hybrid chassis slots. PXI Express-compatible modules preserve hardware and software compatibility, with the exception of local bus features.
R
R-C time constant	Time required to charge a capacitor to 63.2 percent of its maximum voltage.
reed relay	A type of relay composed of two overlapping ferromagnetic blades hermetically sealed within a gas capsule that is filled with an inert gas.
relay	An electrically activated mechanical device that opens and closes electrical contacts.
resistance	The resistance to the flow of electric current. One ohm (Ω) is the resistance through which one volt of electric force causes one ampere to flow.
RF	radio frequency—Refers to frequencies below the infrared range.
RF multiplexer	A switch capable of selecting one of many RF channels.
rise time	The time for a signal to transition from 10% to 90% of the maximum signal amplitude.
S
scan	The process of cycling through a predefined scan list to when and how to make or break connections.
scan list	A string composed of channel names and characters that define connections, disconnections, triggering, and timing of the scan.
SCXI	Signal Conditioning eXtensions for Instrumentation. The National Instruments product line for conditioning low-level signals within an external chassis near sensors so that only high-level signals are sent to DAQ boards in the noisy PC environment. SCXI is an open standard available for all vendors.
Seebeck coefficients	Temperature coefficients of specific metal-to-metal junctions.
sense	The channel of a DMM used to measure the voltage drop across a resistance in a 4-wire measurement.
settling time	The time required for a signal to reach a steady state after sending an actuation command to the relay.
software trigger scanning	A type of scanning where the scan list advances at every call of niSwitch Send Software Trigger.
solid-state relay	A type of relay incorporating an LED to control the gate of a photo-sensitive MOSFET.
SPDT	single-pole double-throw
SPST	single-pole single-throw
SSR	solid-state relay
switch	A device for routing signals between two points.
switching capacity	The maximum current and voltage that a relay is specified to handle.
switching current	The maximum rated current that can flow through the switch as it makes or breaks a contact.
switching voltage	The maximum signal voltage that the switch module can safely maintain.
synchronous scanning	A type of scanning where the scan list advances after the switch receives a digital pulse from another device.
T
terminal	Named location where a signal is either produced (generated) or consumed (acquired).
terminal block	A group of several terminals, intended for interconnection of circuits, mounted on a solid insulating block.
thermal EMF	The voltage created by the junction of dissimilar metals that increases and decreases with the rise and fall of the ambient temperature.
topology	Organizational representation of the channels and relays in a switch module.
transistor	A device used to amplify a signal or open and close a circuit.
V
VA	volt-ampere—A measurement of power. The volt-ampere rating is sometimes used if the rated equipment has significant phase shift between the current and voltage. Hence, the volt-ampere rating gives a power rating that ignores this phase shift.
VI	virtual instrument
voltage	the electromotive force
voltage standing wave ratio	The measure of signal reflection in a propagating signal.
VSWR	voltage standing wave ratio

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