The deviation between actual value and the expected, ideal value. Absolute accuracy specifies the degree of accuracy that exists in comparison to primary or secondary standards under all specified operating conditions. Typical accuracy is sometimes called relative or nominal accuracy. It assumes that a fixed set of operating conditions exist, and that the instrument parameters statistically average to provide a typical operating accuracy throughout its measuring range.
ACE (Asynchronous Communication Element)::
Another name for UART q.v.
For DC voltage measurements, an active electronic filter may be used to reject input noise in some instruments. An active filter is much more effective than passive filtering and assures high normal-mode rejection of 60db minimum.
ADC (A/D) (Analog to Digital Converter)::
An ADC is a device which accepts an analog signal such as temperature and converts it to an equivalent digital signal. The analog input has to be sampled at fixed intervals in order to provide an accurate digital output. The digital output code represents the magnitude of the input signal. The analog-to-digital converter is the heart of the digital voltmeter. It comprises of the circuitry which compares the input voltage amplitude to a precision reference voltage and determines the input voltage amplitude, which is then convened to coded digital logic-level outputs suitable for operating a digital readout and sometimes for operating external digital-data-utilising equipments.
A false lower frequency component that appears in analog signal reconstructed from original data acquired at an insufficient sampling rate.
A computer program that is written to accomplish a specific task
Data arranged in single or multidimensional rows and columns.
ASCII (American Standard Code for Information Interchange): :
A 7 or 8 bit code established by the American National Standards Institute (ANSI) to achieve compatibility between data services. Compatible with the International Standards Organisation (ISO) 7/8 bit code. Details of the code will normally be found in the computer technical reference manual.
Asynchronous Communication: :
Transmission in which each data character is individually synchronised, usually by the use of start and stop bits.
Automatic Polarity: :
A Digital Panel Meter with automatic polarity senses the polarity of the DC voltage connected to its input and makes the proper connections to a unipolar A-to-D converter which digitizes the voltage. In the readout, a minus symbol displays which polarity was sensed in reference to the common input.
In the traditional DPM a zero setting control is needed because ordinary DC amplifiers are subject to zero drift. Automatic zero overcomes the problem by utilizing a circuit which automatically biases the amplifier to a perfect zero just prior to each measurement.
Base Address: :
A unique address set up on an I/O card to allow reference by the host computer. All registers are located by an offset in relation to the base address.
BASIC (Beginners All-purpose Symbolic Instruction Code): :
The most common computer language. BASIC is not rigorously structured and relies on English-like instructions which account for its popularity.
A unit of signalling speed equal to the number of signal events per second. Not necessarily the same as bits per second.
Bias Current: :
The DC current drawn by the input circuit of a DPM is called bias current.
BCD (Binary Coded Decimal)::
A system of binary numbering where each decimal digit 0 through 9 is represented by a combination of four bits. BCD (Multiplexed): Data outputs from digital panel meters, formatted to be character-serial, bit-parallel, binary-coded decimal. Four lines are provided for the 8,4,2,1 BCD character in addition to a strobe line for each decade to identify each BCD character. BCD (Parallel): Character parallel binary-coded decimal is a widely used data format used to operate into data recorders, printers, computers, and programmable test instruments. It is generated by storing the multiplexed BCD in latch circuits so that the BCD characters for all of the decades are available in parallel.
Numbering system in which the only two allowable digits are 0 and 1.
BIOS (Basic Input/Output System): :
The commands used to instruct a CPU how to communicate with the rest of the computer.
A signal being measured is said to be bipolar when the voltage on its 'high' terminal can be either of positive or negative polarity in relation to its 'low' terminal.
Abbreviation of "binary digit". The smallest unit of information. A bit represents the choice between a one or zero value (mark or space in communications technology).
Bit Rate: :
The speed at which bits are transmitted, usually expressed in bits per second.
Broadcast: A broadcast communication involves a packet of data being transferred to every other device on the network simultaneously.
Broadcast storm: A state in which a message that has been broadcast across a network results in more broadcast messages being sent then still more messages in a snowball effect. A severe broadcast storm can block all other network traffic resulting in a network meltdown.
A storage device used to compensate for a difference in rate of data flow, or time of occurrence of events, when transferring data from one device to another. Also a device without storage that isolates two circuits.
Conductors used to interconnect individual circuitry in a computer. The set of conductors as a whole is called a bus. Byte: A binary element string operated on as a unit and usually shorter than a computer word. Normally eight bits.
C: A high level programming language. Developed around the concept of structured programming and designed for high operating speeds. Microsoft C and Borland C are dialects of C.
Calibration Period: Instruments should be periodically checked for calibration accuracy. How often will depend on how much usage and how the instrument is treated. Instruments should be checked each year and if the utilisation is severe a calibration period of 6 months or 3 months should be observed.
Category 5/5e/6: A cable that comprises 4 twisted-pair wires that is commonly used for Ethernet network cabling. Category 5e and 6 are most commonplace and have superseded Category 5.
Channel: One of several signal/data paths that may be selected.
Character: A letter, figure, number, punctuation or other symbol contained in a message or used in a control function.
Character Set: The set of characters that can be coded and/or printed by a particular machine.
Clear: Restore a device to a prescribed initial state, usually the zero state.
Client: In a Client-Server relationship, the client is the device or software that initiates a connection to a server. The client initiates communications and stays connected to the server all the time there is a requirement for data to be exchanged. TCP operates on a client-server basis.
CTS (Clear To Send): A control signal, defined in the RS-232 standard, to indicate that Data Communication Equipment (DCE) is ready to transmit.
Clock: A device that generates accurate, periodic signals for synchronisation purposes.
CMOS (Complementary Metal Oxide Semiconductor): This is a leading design technique used to produce large scale integrated (LSI) circuits employed in most modern microelectronic equipments.
Code: A set of unambiguous rules specifying the way in which characters may be represented. It is also another term for the text of computer software.
Cold Junction: The junction of a thermocouple (see thermocouple) to a measuring instrument, as opposed to the Hot Junction which is used to measure the temperature.
Cold Junction Compensation (CJC): A technique to compensate for thermocouple errors made when the reference or cold junction is at a temperature other than 0ï¿½ C. Generally the instrument cold junction will be at room temperature or higher depending on internal heating. An internal sensor is used to measure this temperature to compensate for the thermocouple junction offset.
CMR (Common Mode Rejection Ratio): Common Mode Rejection states the ability of the equipment to reject noise which appears between the input terminals (high and low) and ground CMR is needed only when the equipment ground is different than the ground of the source being measured. When the equipment is operated from a line source of power or when both high and low inputs are raised above ground, coupling (impedance) paths exist which introduce noise. Highest CMR exists in a battery operated DMM. Particular care should be taken when data outputs are used for above ground measurement data outputs and inputs must be isolated through the use of optoisolation. A measure of the equipment's ability to reject common mode interference. Usually expressed in decibels as the ratio between the common mode voltage and the error in the reading due to this common mode voltage.
CMV (Common Mode Voltage): This specifies the DC voltage which is tolerable between input low and power ground. When the equipment is operated from logic level power the CMV is apt to be in the order of 0.5 VDC or less. Using batteries or a transformer-isolated power supply permits an instrument to be operated at a higher CMV, usually in the order of 100 VDC when related to panel instrumentation. In a differential measurement system, the common mode voltage usually represents an interfering signal. The common mode voltage is the average of the voltages on the two input signal lines with respect to ground level of the measuring system.
Communication Turnaround: Changeover from transmit to receive or vice versa in a half duplex system.
Conversion Rate: Conversion rate specifies the number of readings per second the A-to-D converter can produce. In many cases the conversion rate may be faster than the settling time and therefore the digital meter may be able to produce several readings before settling to full accuracy. Usually for a few digits change in reading, the settling and conversion times are the same.
Conversion Time: The time required, in an analog/digital input/output system, from the instant that a channel is interrogated (such as with a read instruction) to the moment that an accurate representation of the data is available. This could include switching time, settling time, acquisition time, converter processing time etc.
Crest Factor: When making true RMS AC voltage measurements there are limitations in accuracy imposed by the crest factor of the waveform being measured. Crest factor is defined as the peak value divided by the RMS value.
CREST FACTOR = V Peak/Vrms
DAC (D/A) (Digital to Analog Converter): A DAC converter receives a digital input signal and converts it to an equivalent analogue value. The magnitude of the output signal represents the value of the digital input.
Data Acquisition or Data Collection: Gathering information from sources such as sensors and transducers in an accurate, timely and organised manner.
DCE (Data Communication Equipment): The equipment that provides the functions required to establish, maintain and terminate a connection, and provides the signal conversion required for communication between data terminal equipment and the telephone line or data circuit. See Modem
DTE (Data Terminal Equipment): A computer or other terminal that provides data in the form of digital signals at its output.
DCD (Data Carrier Detect): A control signal, defined in the RS-232 standard, generated by DCE to indicate that it is receiving a valid signal.
DSR (Data Set Ready): A control signal, defined in the RS-232 standard, to indicate the status of DCE
DTR (Data Terminal Ready): A control signal defined, in the RS-232 standard, to indicate the status of DTE
dB (Decibel): A logarithmic representation of the ratio between two signal levels.
Default: The values or options that are assumed when not specified.
Digit: Digit is a word with more than one meaning in discussing digital voltmeters. A four-digit panel meter is one having four decimal decades eg 9999. Accuracy of one digit implies an accuracy of one count in the least significant decade.
Digital Signal: A discrete or discontinuous signal; one whose various states are identified with discrete levels or values.
DIP Switch: A set of switches contained in a "Dual In-line Package" for mounting on a printed circuit board.
Display Inhibit (Blanking and Dimming): In some DPM applications it is advantageous to inhibit or blank the LED readout. It saves power and reduces readout clutter when the instrument is not in use. Some DPMs have the power line for the LED readout available separately at the input connector. Power to the readout is switched to provide a display at the operator's discretion. If a potentiometer is connected in series with the readout then the intensity of the readout may be adjusted to the brilliance most comfortable for each individual operator.
DMA (Direct Memory Access): This is a process whereby the I/O controller gains temporary control over the CPU's memory, while the program is running, to allow a single word or a group of words to be read or written. The I/O process obtains direct access to the memory.
DMM (Digital Multimeter): A multi range analog input, analog to digital converter and digital display.
DPM: (Digital Panel Meter): A single range analog input, analog to digital converter and digital display.
Drift: Small variations in a measured parameter over a period of time.
Drivers: Part of the software that is used to control a specific hardware device.
Dual-Slope Conversion: The dual-slope A/D conversion technique or variations thereof is the most common used in digital meters. The technique uses an operational amplifier connected as an integrator, and a digital counter-timer. There are two steps to the conversion. The input is connected to the integrator and the feedback capacitor is charged for a fixed period of time, generally related to the line frequency. The integrator averages transient noise on the input and noise related to line frequency is cancelled. Upon completing the integration of the input signal the counter has reached a zero reading At this point the input is disconnected and a precise negative reference voltage is connected to the integrator which discharges the feedback capacitor while the counter counts. When the integrator output reaches zero the counter is stopped. The counter reading represents the voltage reading and is displayed by a numerical digital readout. The conversion is completed in less than a second. In addition to excellent noise rejection this conversion technique eliminates errors from the drift in component values.
DVD-R: DVD-ROM that can be written to once, much like CD-R.
DVD-RAM: Re-writable version of DVD, Drives can also read DVD-ROM and CDs.
DVD-ROM: Read only DVD media, Drives can also read CDs.
DVD-RW: Re-writable version of DVD.
Dynamic Link Library (DLL): A library of functions used by Windowsï¿½ programmers
GPIB (General Purpose Interface Bus): This is also referred to as the IEEE-488 bus, the HP-IB or the IEC 625 BUS. It is a widely used bus for the control of instrumentation.
Ground: An electrically neutral wire having the same potential as the surrounding earth. Provides a reference point for an electrical system.
Half Duplex: Refers to a communications system or equipment capable of communications in both directions, but only one at a time.
Handshaking: Exchange of predetermined codes and signals between two data devices to establish and control a connection.
Hardware: The visible parts of a computer system such as the circuit boards, chassis, peripherals, cables etc. It does not include data or computer programs.
Half duplex: Data transmission that can occur in two directions over a single line, but only one direction at a time.
Hertz: A unit of frequency equating to one cycle per second.
Hex (Hexadecimal): This is a numbering system which uses a base of 16. The symbols used to represent the digits are 0,1 ,2,3,4,5,6,7,8,9,A,B,C,D,E,F (F = 15 in decimal). For example the value FF hex = 255 decimal = 11111111 binary. The numbering system to base sixteen.
Input Impedance: Instruments often require a high input impedance to prevent their high sensitivity and accuracy from being affected by loading errors. In DPMs 1Megohms input impedance is not unusual.
I/O (Input/Output): The process of transferring data from or to a computer system including communication channels, operator interface devices or data acquisition and control channels.
Interface: A shared boundary defined by common physical interconnection characteristics, signal characteristics and meanings of interchanged signals.
Interrupt: An interrupt breaks into the computers program of instructions to carry out a particular routine. It is a way of controlling input/output activity in which a peripheral device sends a signal to interrupt the programme in order to send or receive data. To signal a process to take a specific action.
IP: Internet Protocol is a standardized method of transporting information across the Internet or in Ethernet based LANs. It is typically used in conjunction with TCP, which assembles the packets once they have been delivered to the intended location. Internet Protocol version 6 (IPv6) is the designated successor of IPv4 which is the current version of IP used on the internet.
IP Address: An IP(v4) address is a 32-bit number, which identifies a specific computer in an IP network.
An IP(v6) address is a 128-bit number, which identifies a specific computer in an IP network
IP camera: An IP camera is an image recording device comprising lens, image sensor and image processor capable of transmitting
video across an IP-based network, typically Ethernet in a LAN environment.
Isolation Voltage: The voltage which an isolated circuit can withstand. Isolation voltage is specified between two or more points
LACP: The Link Aggregation Control Protocol is typically implemented between switches to allow multiple physical connections to form one logical connection. This has the benefits of higher bandwidth and redundancy across the link.
Latch: A term that indicates that the state of a digital signal will remain stored until change by another command.
LCD (Liquid Crystal Display): Digital instruments employ LCD readouts because they utilize miniscule amounts of power making them excellent for battery operated instruments. LCDs are best in high ambient light levels as they do not wash out but instead gain greater contrast in bright light.
Leading Zero Suppression (Blanking): Some digital panel meters have a control output line which permits leading zero suppression. This is accomplished by connecting a decimal point select line to the suppression control. Zeros to the left of the decimal point selected will be blanked. Digits other than zero will not be suppressed.
LSB (Least Significant Bit): In a system in which a numerical magnitude is represented by a series of digits, the least significant bit (binary digit) is the digit that carries the smallest value or weight.
LED (Light Emitting Diode): LED displays provide a bright clear numeric presentation of readings in digital instruments. They are generally best for indoors environments and can be viewed from a greater distance in normal lighting conditions. Most LED displays are red but are also available in yellow and green.
Linearity: The linearity of a digital voltmeter is the inaccuracy in reading which results when reading of the instrument is plotted against the actual absolute voltage input, from zero to full scale. For a perfect DPM the function is a straight line. Linearity is the greatest deviation from a straight line expressed as a percentage of full scale.
Logic Gate: An electronic device which implements an elementary logic function. The functions are OR, AND, NOR, NAND, XOR and NOT. A high voltage level output from the gate normally indicates a TRUE state (1) and a low voltage level output indicates a FALSE state (0).
Loop-back Test: A test of a communications link performed by connecting the equipment output of one direction to the equipment input of the other direction and testing the quality of the received signal.
Modem (MOdulator-DEModulator): A type of DCE that converts digital data to an analog signal for transmission on telephone circuits. A modem at the receiving end converts the analog signal to digital form.
Monotonic: A DAC is said to be monotonic if the output increases as the digital input increases, with the result that the output is always a single valued function of the input.
MOSFET (Metal Oxide Semiconductor Field Effect Transistor): A type of transistor which uses an electric field to control the operation of the transistor. They operate at higher switching speeds and lower currents than bipolar transistors.
MPEG4: Moving Picture Experts Group Compression Standard Version 4. MPEG4 is a technology for compressing voice, video and related control data and is one of the MPEG international standards
MSB (Most Significant Bit): In a system in which a numerical magnitude is represented by a series of digits, the most significant bit (binary digit) is the digit that carries the greatest value or weight.
Multi-drop: A system of serial communication that allows multiple transmitter/receiver combinations to be connected to a single transmission line.
Multicast: Bandwidth-conserving technology that reduces bandwidth usage by simultaneously delivering a single stream of information to multiple network recipients. It is neither a broadcast or a unicast.
Multiplexer: A multiple way analog switch q.v., where a single path through the switch is selected by the value of a digital control word.
Multimode: A type of fibre optic cable where the core diameter is much larger than the wavelength of light transmitted. Two common multimode fibre types are 50/125 and 62.5/125 microns.
Noise: An undesirable electrical interference to a signal.
NMR (Normal-Mode Rejection): This is the amount of noise superimposed on the input signal of a DC digital voltmeter which the instrument is capable of rejecting. It is expressed in decibels. NMR is enhanced by passive and active filters as well as integrating techniques of ND conversion. It is not a good policy to rely on a DPM to reject noise. A good clean signal should be obtained by using appropriate signal conditioning techniques external to the DPM. Also called series mode.
NMS (Normal Mode Signal): Aka Series mode signal. In a differential analog measuring system, the normal mode signal is the required signal and is the difference between the voltages on the two input signal lines with respect to ground level of the measuring system.
NVR (Networked Video Recorder): An NVR is a video recording platform designed to work exclusively with IP video feeds from IP cameras and video servers on an Ethernet backbone.
Octal: A numbering system which uses a base of 8. The symbols used to represent a numerical value are 0, 1, 2, 3, 4, 5, 6 and 7. For example the value 23 decimal is 27 octal.
Offset: (a) A fixed, known voltage added to a signal. (b) The location of a register above the base address.
Optoisolator: A type of semiconductor which achieves electrical isolation by transmitting signals by light pulses.
Optical Isolation: Two networks coupled only through an opto-electronic sender and receiver with no electrical conductivity between the two networks.
Overload Protection: Input overload protection is provided in digital instruments to protect the meter from damage whenever voltages in excess of the measuring range are applied to the input. In measuring voltage, the intrinsic high input impedance provides protection in most cases.
Over-Range: An input device with a measurement range of 0-10V may be able to read above this value by a small amount. After a nominal amount the instrument is said to be "over-range" and this may be indicated by flashing digits on a panel meter for example.
PAL (Programmable Array Logic): This is an Integrated Circuit (IC) with an array of interconnected logic gates. The interconnections between logic gates are removed by blowing fusible links in order to produce the required final logic.
Parity Bit: One of the bits that may be incorporated in a character to be used as a simple form of error detection.
Pascal: A high level programming language originally developed as a tool for teaching the concepts of structured programming. It has evolved into a powerful general-purpose language popular for writing scientific and business programs. Borland Turbo Pascal is a dialect of Pascal.
Polarity Inhibit (Blanking): In some applications of bipolar digital panel meters it is desirable not to display the polarity sign. Such is the case for AC or ohms measurements. In many digital panel meters a control line is provided for blanking the polarity sign from a remote contact-closure or logic-level change.
Port: An interface on a computer capable of communication with another device.
PROM (Programmable Read Only Memory): A non-volatile memory which is programmed by blowing fusible links using special equipment.
Protocol: The rules for communication between like processes, giving a means to control the orderly communication of information between linked stations.
Range: Refers to the maximum allowable full-scale input or output signal for a specified performance.
Resolution: A binary converter is said to have a resolution of n-bits when it is able to relate 2n distinct analog values to the set of n-bit binary words.
RI (Ring Indicator): A control signal, defined in the RS-232 standard, to indicate that DCE is receiving a ringing signal.
RS (Reference Standard) 232/422/485: Designations of various recommendations formulated to standardise the application of serial communication between connected computers, terminals, modems, instruments etc.
RTD (Resistance Temperature Detector): The RTD is a finely wound temperature sensor whose resistance varies linearly and accurately with temperature. It is supplied in ribbon form with an adhesive back ready to apply to smooth or rough surfaces for sensitive, accurate temperature monitoring.
RTS (Request To Send): A control signal, defined in the RS-232 standard, generated by DTE to instruct DCE to transmit
Routing: The function of determining the route a packet (typically IP) should take from a subnet to get to another subnet. Routing is the process of delivering a message across a network or networks by the most appropriate path.
Unicast: In computer networking a unicast is the sending of information packets to a single destination rather than sending to many recipients simultaneously.
RSTP: RSTP is an evolution of the Spanning Tree Protocol. Rapid Spanning Tree Protocol (RSTP) provides faster spanning tree convergence after a topology change hence much better network recovery times in the event of a cable or connector failure.
Redundant ring: A redundant ring is a topology commonly employed in Industrial Ethernet networks. Layer 2 switches are connected in a ring (typically by copper or fibre optic cables) to provide media redundancy. If a cable is broken or a connector accidentally unplugged the network will continue to function with no perceivable loss in performance. Network recovery times are typically sub-second as opposed to the Spanning Tree or Rapid Spanning Tree protocols that take considerably longer.
Sample and Hold: Sample and hold signal conditioners are used in conjunction with digital panel meters to acquire fast instantaneous voltage readings which are programmed in time at any position of a waveform. A typical sample and hold measures amplitudes up to ï¿½10 volts. Upon application of a logic one to a control line, the sample and hold acquires and its output tracks the waveform until the logic level is returned to zero. At that point on the waveform the amplitude is held by the sample and hold the DPM then reads the output of the sample and hold.
Scroll: To move the display so that new information may appear.
SCSI (Small Computer Systems Interface): A fast and flexible data interface between your PC and data storage devices.
Serial Transmission: A method of information transfer in which the bits comprising a character are sent in sequence one at a time.
Settling Time: The time taken for the signal appearing at the output of a device to settle to a new value caused by a change of input signal.
Software: The non-physical parts of a computer system that includes computer programs such as the operating system, high level languages, applications program etc.
Source Code: A non-executable program written in a high level language. The source code must be translated by a compiler or assembler into object code that is understood by the computer.
Space: One of two possible states of a binary information element.
Start Bit: The first bit transmitted in the asynchronous transmission of a character to synchronise the receiver.
Stop Bit: The last bit transmitted in the asynchronous transmission of a character to return the circuit to the at-rest condition.
Symbol: The graphical representation of some idea. Letters and numerals are symbols.
Singlemode: An optical fibre that supports only one mode of light propagation above the cut-off wavelength. Singlemode fibre is typically 9/125 microns (core to cladding ratio)
Simplex: In simplex operation, a network cable can only send information in one direction.
STP: A pair of insulated wires which are twisted together. The pair is wrapped with a metallic foil or braid that has the effect of insulating the pair from electromagnetic interference. The shield should be grounded at one end during installation.
Industrial Ethernet: Industrial Ethernet is the name given to the use of the Ethernet protocol in an industrial environment. Rugged Ethernet switches and converters are used to build Industrial Ethernet networks.
STP: The Spanning Tree Protocol is a method of preventing broadcast storms when Ethernet is configured in a mesh or ring topology. It allows redundant networks to be built. STP is slow and has mostly been supersede by RSTP
Subnet: A subnet is a portion of an IP network defined that is defined by a subnet mask. Devices on the same subnet have the same subnet mask
Subnet mask: A binary construct (same number of bits as the IP address) used for dividing IP networks into a series of subgroups or subnetworks.
Server: A server is a networked device that provides services to other devices, known as clients, over a network. A computer is typically a server and a specific instance of software running on the server is the 'service'.
Is a protocol that enables two network devices to connect to one another and exchange bi-directional streams of data. The protocol ensures that the data is transferred and guarantees that the data is received in the same sequence in which it was sent. It is more reliable but slower than User Datagram Protocol (UDP).
Thermocouple: A thermocouple is made up of two dissimilar metal conductors, known as thermoelements, joined so as to produce a thermal EMF which varies with temperature.
Thermocouple Measuring Junction: The junction of a thermocouple which is subjected to the temperature being measured (aka Hot Junction).
Thermocouple Reference Junction: The junction of a thermocouple which is at a known temperature( aka Cold Junction).
Token Ring: Token ring is a LAN architecture (a legacy alternative to Ethernet) whereby all computers are connected in a ring and a token passing scheme is used to manage access to the network. The device with the token is the only one that can transmit data at any given time.
Transmission Turnaround: Switching the transceiver from transmission to reception and vice versa in a half-duplex circuit.
See Communication Turnaround.
Turnaround Time: The actual time required to reverse the direction of transmission from sender to receiver, or vice versa, when using a half duplex circuit.
UART (Universal Asynchronous Receiver/Transmitter) aka ACE: A device which performs asynchronous communication functions by converting parallel digital data into serial bit transmission and vice versa.
Unipolar: A signal being measured is said to be unipolar when the voltage on its 'high' terminal is always the same polarity (normally positive) in relation to its 'low' terminal.
UTP: Unshielded Twisted Pair cabling comprises of pairs of insulated conductors wound together for the purposes of canceling out electromagnetic interference thus increasing the integrity of the transmitted data.