- Electromotive Force (emf)
- Difference of potential produced by sources of electrical energy which can be used to drive currents through external circuits. Unit is the volt.
- Endurance limit
- In fatigue testing, the number of cycles which may be withstood
without failure at a particular level of stress.
- Electronic Industries Association.
- A local area network to which you can connect data acquisition
- E-Type Thermocouple
- Chromel-constantan thermocouple with a temperature range of 0 to 800 oC.
- The voltage or current applied to a transducer.
- External Trigger
- A trigger is something that causes data acquisition to start. External triggers let you synchronise data acquisition
with external events, for example when you switch on a machine. For more information and examples see Issue 45 of the Monitor newsletter.
- Fall Time
The time a signal takes to change from a specified high value to a specified low value. Usually measured as the time to fall from 90% to 10% of the step height or maximum amplitude.
- Unit of capacitance.
- A temperature scale where the freezing point of water is 32 degrees and the boiling point 212 degrees. Superceded for scientific purposes by Celsius. Symbol is F.
- Fast Fourier Transfer (FFT)
- An analysis algorithm - given a finite set of data points, the FFT expresses the data in terms of its component frequencies.
- FIFO buffer
- A first in, first out, store. The first value placed in the buffer
(queue) is the first value subsequently read.
- Attenuates components of a signal that are undesired: reduces
noise errors in a signal. More details on filters are in Issue 8 of Monitor.
- Flow Control
- See Handshaking.
- Measured in hertz (cycles per second), rate of repetition of changes.
- Frequency Counter
- Counts digital pulses over a defined gate time. A typical gate
time is between 0.1 and 10 seconds.
- Front panel
- The front surface of a unit, generally containing switches and
- Full Scale Output
- The difference between the minimum output (normally zero) of a data acquisition device and the rated capacity.
- Amplification of a circuit.
- Gain Range
- The maximum and minimum voltage that will be digitised by the A-D converter is sometimes called the gain range.
- When your computer wishes to send a message to a device on another subnet it sends the message via a Gateway. This is another computer which relays the message to the destination address. Your computer needs to know the IP Address of the Gateway. You can view this in the TCP/IP properties of your computer.
- Geographic information system. Where data is assembled, stored, displayed and identified according to its location.
- General Purpose Interface Bus. Also known as IEEE-488 bus. The GPIB standard was designed to connect several instruments to computers for data acquisition and control. Data can be transferred over GPIB at 200 000 bytes per second, over distances of 2 metres.
- General Packet Radio Service.
- See earth.
- When data is collected by remote sensing techniques, ground-truthing confirms that the information is accurate. Ground-truthing is collecting data by non-remote sensing means.
- The RS232 protocol includes handshaking (also known as flow control). Although this is often not necessary, it has two functions: tt allows the computer to stop your instrument from sending data when the PC is not ready for it; it allows your instrument to prevent the PC from sending data when the instrument not ready for it. More on handshaking.
- Hardware Trigger
- See External Trigger.
- Highway Addressable Remote Terminal. Provides digital communication to microprocessor-based (smart) analogue process control instruments.
- Hertz (Hz)
- Cycles per second unit of frequency.
- Counting system based on 16.
- High Pass Filter
- When a low-level transducer signal is superimposed on a large dc output voltage, a high-pass filter might be useful. This attenuates (removes) low frequencies. Using a cut-off frequency of, say, 4 Hz, will eliminate the dc voltage which has a frequency of zero. A high-pass filter will remove "drift". This can be a particular problem with biological and chemical signals, but not usually with modern electronic signals. See Issue 8 of our newsletter for more information.
- Human machine interface (hmi)
- Also known as man machine interface. The communication between the computer system and the people who use it.
Symbol for electric current.
A 2-wire serial bus developed by Philips.
Input/Output. A data acquisition system monitors signals through its inputs, and sends control signals through its outputs.
Integrated Circuit (electronic components fabricated on a semiconductor substrate which cannot be divided without losing its function).
Institute of Electrical and Electronics Engineers. An American Society that, amongst other things, establishes international standards in the computing, electronic and telecommunications
- IEEE-488 Bus
- See GPIB.
Interface Management Language. A programming language used to communicate with measurement instruments.
The magnitude of a magnetic field created by a circuit carrying a current. This can cause higher voltages in the circuit.
Data entering a device from the environment. A signal being monitored by a data acquisition system.
Any item of electrical or electronic equipment which is designed to carry out a specific function or set of functions. For example an electronic balance, a gas analyser or a chromatograph.
- Integrated Circuit
Electronic components fabricated on a semiconductor substrate. An integrated circuit cannot be divided without losing its function.
A positive or negative whole number, or 0.
- A shared boundary. It might be a piece of hardware used between two pieces of equipment, or a software display communicating between the computer system and the people who use it.
Software enabling a computer to run programs statement by statement.
An external signal causing the execution of a program to be suspended.
- Integrating A-D Converter
An integrating A-D converter averages the input signal over a length of time. This is useful when the signal to be measured fluctuates slowly. By averaging the signal the converter helps reduce unwanted signal contamination (noise).
- Integration Time
The time over which an integrating A-D converter averages the input signal. If chosen appropriately will average over a complete mains cycle thereby helping to reduce mains frequency interference.
A dc-ac converter.
- Industry Standard Architecture. An ISA expansion slot lets you plug data acquisition boards into PCs.
- Infrared Data Association. A Nonprofit organisation whose goal is to develop globally adopted specifications for infrared wireless communication.
International Organization for Standardization, which is made up of national members. A member is the "most representative of standardisation in its country". For example BSI (British
Standards Institute), DIN (Deutsches Institut für Normung) and ANSI (American National Standards Institute).
- IP Address
Each computer on the network has an IP Address. This is in reality a 32 bit binary number. Since such numbers are not user friendly they are usually presented in Dotted Decimal Notation. This splits the 32 bits into 4 eight bit chunks. Each chunk is then converted to a decimal number in the range 0 to 255. For example -
01011001 00011101 11001100 00011000 becomes 220.127.116.11
You can think of this address as being roughly like a postal address arranged as Country / City / Street / House Number. See also Static and Dynamic IP Address.
Two circuits are isolated when there is no direct electrical connection between them.
- Isolation to Earth or System
A high transient voltage at one input may damage not only the input circuit, but the rest of the data acquisition hardware, and, by propagating through the signal conditioning and A-D circuits,
eventually damage the computer system as well. You can prevent this type of damage by isolating the input from the earth of the data acquisition and computer hardware.
- Isolation Between Inputs
A transient at an input can also propagate to other equipment connected to that input. This is prevented by providing isolation between inputs.
- J-Type Thermocouple
Iron-constantan thermocouple with a temperature range of 0 to 750 oC.
A symbol for a thousand, from kilo.
A unit of stored data. 1K = 210 = 1024. Also stands for a degree on the Kelvin temperature scale.
A temperature scale which is one of the seven base units in the International System of Units (SI). Symbol is K.
- K-Type Thermocouple
Chromel-Alumel thermocouple with a temperature range of -200 to 1200 oC.
- A Line Feed. A "non-printing" character which often terminates a message from an instrument plugged into the computer's COM port.
Local area network. A data communication system connecting devices in the same vicinity. Data is transferred without the use of public communications. Examples of LANs are Ethernet,
token ring and Modbus.
- Least Significant Bit, LSB
In a binary number, the 1 or 0 furthest to the right.
Last in first out. Describes a stack method of data storage.
Laboratory information management system.
- Ideally an A-D or D-A converter converts the input or output range into equal steps. In practice the steps are not exactly equal. Linearity, or non-linearity, is a measure of how close the steps
- Load Cell
A transducer which converts a force into an electrical signal. It normally comprises four strain gauges in a wheatstone bridge arrangement.
- Low Pass Filter
- This lets through the lower frequencies and attenuates the higher frequencies. Choose the cut-off frequency to be compatible with the unwanted frequencies, the frequencies present in the signal you are measuring, and the sampling rate of the analogue-to-digital converter. See Issue 8 of our newsletter for more information.
- Linear Variable Differential Transformer. Used in measuring devices that convert changes in physical position to an electrical output.
- Symbol for metre and milli- (thousandth).
Symbol for mega (million).
Source of electrical power, normally the electricity supply system.
- Mains Frequency
Electricity ac supply frequency; 50 Hz in UK, 60 Hz in US.
Manufacturing Execution System.
The SI fundamental unit of length, equal to 1.093 yards. (Meter in US.)
Manufacturing Information System.
Man Machine Interface. Also known as human machine interface. The communication between the computer system and the people who use it.
Form of construction in which hardware or software units, often with differing functions, are quickly interchangeable.
Where each signal is switched in turn to a single analogue-to-digital converter. As opposed to where one A-D converter is used for each signal in simultaneous sampling.
An industrial networking system that uses peer-to-peer communications. More details on Modbus are in Issue 32 of Monitor.
- Most Significant Bit, MSB
In a binary number, the 1 or 0 furthest to the left.
- N-Type Thermocouple
- Nicrosil-Nisil thermocouple with a temperature range of -200 to 1200 oC.
- Name Server
When comunicating with instruments over a TCP-IP network, and your computer wishes to send a message to a named destination, it asks a Name Server to resolve the name to an IP Address. Your computer needs to know the IP Address of the Name Server. You can view this in the TCP/IP properties of the computer.
- Negative Edge Trigger
Data acquisition starts when an input signal changes from a high to a low state.
The physical interconnection of devices sharing a communications protocol.
A device with a direct point of access to a network.
Any unwanted electrical signals contaminating the signal to be measured. This noise may be electronic noise which is an artefact of semiconductor construction techniques and is not reducible.
Alternatively the noise may be caused by environmental factors. This type of noise can be the result of poor positioning or screening of signal wiring. This may result in mains frequency or RF pickup contaminating the required signal.
A product outside manufacturing limits but not necessarily defective.
- Non-Destructive Testing
Method of inspecting materials and products without affecting their subsequent properties and performance. Abbreviation NDT.
The US National Television System Committee and their standard colour television system. Modified or 4.43 NTSC has the colour subscarrier at the European frequency of 4.43 MHz instead of 3.58 MHz.
- Nyquist Theorem
The Nyquist theorem demands that a signal be sampled at at least twice its maximum frequency. To get an accurate picture of a waveform however, a sampling rate of 10 - 20 times the highest frequency is better.
Original Equipment Manufacturer. A company which makes basic computer hardware for other manufacturers to build into their products.
- Offset Error
If you get a reading other than zero for a zero condition then you have an offset error: every reading will be inaccurate by this amount.
SI unit of resistance, such that one ampere through it produces a potential difference of one voltage.
- On-Off Control
A simple control system which is either on or off.
Information leaving a device.
- Output Source Current
See Current Source.
- Output Sink Current
See Current Sink.
- Phase Alternation Line
The colour television coding system generally used for European broadcasting.
- Phase Alternation Line
The colour television coding system generally used for European broadcasting.
- Personal computer. Generally applied to computers conforming to the IBM designed architecture.
- Peripheral Component Interconnect
A local bus standard developed by in 1992. PCI cards plug into your computer and are configured through software. They do not have jumpers or switches.
- Personal Computer Memory Card International Association
Industry group that developed the specification for credit card-sized plug-in cards for laptop computers.
- Peer-to-Peer Communication
- A communication between networked devices in which any device
can initiate data transfer.
Proportional gain, integral action time and derivative action
time. PID software, for example, compares an analogue input
value with a set point and if there's a discrepancy outputs an
appropriate analogue or digital control value, according the PID
Piping and instrumentation diagram.
- Ping Utility
This is a test utility which sends a message to a defined port within your instrument. The instrument replies with a short data message. Virtually every unit on TCP/IP will support this action. If you cannot Ping your instrument, and it is on a TCP/IP network, you will not be able to talk to it.
Programmable Logic Controller.
A relay contact.
- The external connector on a device.
- Postive Edge Trigger
Data acquisition starts when an input signal changes from a low to a high state.
- Positive Temperature Coefficient
An increase in resistance due to an increase in temperature.
A set of rules used in data communications.
A temporary change in voltage of any length.
- Quality assurance.
- Ramp Voltage
A steadily rising voltage.
The maximum and minimum allowable full-scale signal (input or
- Reed Relay
Consists of two thin magnetic strips (reeds). When a coil close
to the reeds is energised, they are magnetised and drawn
together making a connection between leads attached to the reeds.
- Electromechanical device that opens or closes contacts when a
current is passed through a coil.
- Relative Accuracy
- How accurately a change in signal is measured. See also Absolute Accuracy.
- The ability of an instrument to give the same reading under
repeated identical conditions.
- The precision with which a measured value can be repeated.
- Resistance Temperature Device (RTD)
- Resistance temperature devices (or detectors) rely on the
principle that the resistance of a metal increases with
temperature. When made of platinum, they may be known as
platinum resistance thermometers (PRTs). See Issue 5 of our newsletter for more information on RTDs.
A measure of the smallest change that can be detected.
- Response Time
The time a system takes to respond to a given input. For example: the time between software sending a message to an instrument and the instrument sending a reply, or the time a sensor takes to indicate a change in conditions.
- Rise Time
The time a signal takes to change from a specified low value to a specified high value. Usually measured as the time to rise from 10% to 90% of the step height or maximum amplitude, but sometimes over 5 to 95%.
Root mean square. The square root of the sum of the squares of a
set of quantities divided by the total number of quantities.
Used when monitoring ac (alternating current) signals. Many
power supplies, for example, issue an ac signal. This needs to
be converted to a dc (direct current) signal for the PC
interface. The solution is a signal conditioning input that
produces a dc signal proportional to the rms of the amplitude of
the input signal. The rms operation means the reading will
always be positive.
An EIA (Electronic Industries Association) standard that defines
a protocol for serial data communications. An RS232 link will
run at up 38400 baud (bits per second) over short distances, and
at lower speeds as the distance increases. You can plug the
RS232 lead directly into the computer's serial (COM) port.
Again, an EIA protocol for serial communications. Each signal line comprises two twisted wires. The voltage-difference between the two lines shows the signal value, rather than the voltage-level. You can connect 10 devices to a single cable
Another EIA protocol for serial communications. Allows 32
devices to be connected to a single cable, distributed over a
Remote Terminal Unit. A data acquisition device at a remote location which transmits data back to, and accepts commands from, a central PC (or other controller).
- Sample and Hold
- A component of a type of analogue-to-digital converter. The
analogue signal is frozen in a sample and hold circuit to
prevent it changing during digitisation. For more information on
A-D converters see 3 of Monitor.
- Sample and Hold Aquisition Time
- See Aquisition Time.
- Sampling Rate
- The number of samples, or readings, per second of an analogue signal.
- Normal channel scanning in a data acquisition system involves stepping round and reading each input channel in turn. The scan will return to the first channel once all the channels have been sampled.
- Supervisory control and data acquisition - a large scale software package usually used to monitor and control a manufacturing process.
- Seebeck Effect
- The principle that describes how a thermocouple works. In a circuit in which there are junctions between dissimilar metals, an electromotive force (voltage) is set up when the junctions are at different temperatures.
- A data acquisition module with a stable on-board reference voltage that software can use for automatic recalibration.
- A measure of the minimum change in an input signal that an instrument can detect.
- A device that can detect a change in a physical quantity (light or pressure for example) and produce a corresponding electrical signal.
- Serial Communication
- Where data is transferred one bit at a time.
- Settling Time
- When a change in signal occurs, the time taken for the input or output channel to settle to its new value.
- Set Point
- Value of a controlled variable, departure from which causes a controller to operate to reduce the error and restore the intended steady state.
- International system of units. Abbreviation for Systeme International (d'Unites).
- Signal Conditioning
- Makes a signal suitable for input to an analogue-to-digital converter. For example, a signal may be filtered to remove noise, or amplified to meet the range of the A-D converter.
- General term referring to a conveyor of information.
- Signal to Noise Ratio
- Compares the signal strength to background noise. Abbreviated to SNR or S/N. The ratio is usually measured in decibels (dB). More details on reducing Noise.
- Single-Ended Input
- An analogue input that is measured with respect to a common earth. Single ended inputs are only suitable for signals that are of good size - 100 mV full scale or above.
- Simultaneous Sampling
- When all analogue signals are read simultaneously. This is achieved by providing each input with its own A-D converter, and initiating sampling from a single clock. It ensures that there is no reduction in sampling rate when more signals are connected.
- Sine Wave
- Waveform of a single frequency, indefinitely repeated in time. In practice there must be a transient at the start and finish of such a wave.
- Sink Current
See Current Sink.
- Slew Rate
- The maximum rate of change of an output signal.
- A networked device that is controlled by another, master, device.
- See Signal to Noise Ratio.
- Software Trigger
- A programmed event, such as a specific key press or mouse click, that triggers data capture.
- A coil of wire, usually wrapped around an iron core, that acts as a magnet when carrying a current. Used as an electromagnetic switch or relay.
- Source Current
See Current Source.
- Short pulse of voltage or current - usually undesirable.
- Square Wave
- Wave that alternates between two fixed values. Has very rapid (theoretically zero) rise and fall times.
| | | |
___| |_______| |_____
- The ability of an instrument or sensor to maintain a constant output when a constant input is applied.
- Static IP Address
- An Instrument can have a fixed IP Address which must be allocated to it by a Network Administrator. The allocated address will be appropriate to and unique for the network. Your instrument must have a utility supplied by the manufacturer which will allow the address to be set.
- Steady State Error
- A measure of the accuracy of performance of a control system. In a stable system, the steady state error is the difference between the desired input and the actual input. When the error is large, the resultant output will not match the desired output.
- When a material is distorted by forces acting on it, it is said to be strained. Strain is the ratio of change in dimension to original dimension.
- Strain Gauge
- A sensor that experiences a change in resistance when it is stretched or strained. It is attached to the body subjected to the strain.
- Successive Approximation
- A technique used in A-D converters to measure an analogue signal. It compares the signal with progressively smaller values, each step getting nearer the actual voltage. More details are in Monitor Issue 4.
- Large TCP-IP networks are physically divided into subnets. Two devices which are on the same subnet can send messages directly to each other without the messages being seen by the rest of the network. This reduces traffic in the wider network. The subnet is defined by the Subnet Mask. You can view this via Control Panel and the TCP/IP properties of your computer. This is a dotted decimal arrangement. For two units to be on the same subnet the parts of their IP Addresses which are covered by a 1 in the Mask must be the same. So if the Mask is 255.255.255.0 then the first 3 elements of both IP Addresses must be the same to be on the same subnet.
If a unit whose IP Address puts it onto one subnet is physically plugged into another subnet then you will not be able to talk to it since your messages will be sent to the wrong subnet.
- A large, momentary, increase in the voltage on a power line.
- Combination of several pieces of equipment to perform in a particular manner.
- A device on the GPIB (general purpose interface bus) that sends information to a Listener on the bus.
- Transmission Control Protocol/Internet Protocol. Communications protocols used to connect hosts on the internet.
- Text Format
- Text format refers to information in the ASCII character set. It is unformatted. Each byte in the file contains one character that conforms to the standard ASCII code.
- Coefficient of Resistance The change in resistance of a semiconductor per unit change in temperature, over a specific range of temperature.
- Thermal Conductivity
- A measure of the rate of flow of thermal energy through a material in the presence of a temperature gradient. Materials with high electrical conductivities tend to have high thermal conductivities.
- Popular temperature sensor because of its low cost, wide operating range and ruggedness. Consists of two dissimilar metals joined together, making a continuous loop. When one junction has a different temperature from the other an electromotive force (voltage) occurs. There are several types of thermocouples, constructed from different metals and with differing temperature ranges and accuracies. More details of thermocouples are in Issue 5 of our newsletter, Monitor.
- A temperature sensor. The name comes from thermal resistor. It is a semiconductor that exhibits a large change in resistance as a function of temperature. Most thermistors exhibit a negative temperature coefficient, where resistance decreases as temperature rises. These are referred to as NTC thermistors.
- Number of results produced per unit time.
- The time software should wait for a reply from the instrument before giving up. If no reply is received in this time, an error may be declared. To avoid spurious timeouts set to between five and ten times the normal response time. If you donít know the response time, 5000 milliseconds should be adequate.
- Time stamp
- Information added to data to indicate the time at which it was collected.
- A device which converts a physical quantity into an electrical signal. Examples include thermocouples and photocells. Most sensors are also transducers.
- A short surge of current or voltage, often occurring before steady-state conditions have become established.
- 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.
- Rejection of the final digits in a number, thus lessening the precision but not necessarily the accuracy.
- Abbreviation for transistor-transistor logic. Referring to logic circuits consisting of two or more directly interconnected transistors, to provide conditional switching capability.
- 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.
- T-Type Thermocouple
- Copper-constantan thermocouple with a temperature range of -200 to 400 oC.
- Twisted Pair
- Cable that consists of individual wires wrapped around each other for carrying telephone or computer data. Reduces pickup noise levels in signals.
- 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.
- A signal range that is always positive or always negative, for example 0 to +10 V.
- Uninterruptible Power Supply. Used to keep critical equipment, including computers, running in the event of a mains power failure.
- Universal Serial Bus A serial bus gradually replacing RS232 on PCs because of its higher speed. Generally fitted as standard in new PCs.
- AC Voltage
- The rate of change of displacement; dx/dt.
- 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.
- 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.
- 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.
- Wibree is a new interoperable radio technology for small devices like sports sensors. It was designed by Nokia for applications where ultra low power consumption, small size and low cost were the critical requirements. Wibree has recently been brought into the Bluetooth stable and renamed Ultra Low Power (ULP) Bluetooth. More details of Wibree are in issue 110 of Monitor
- Wireless Fidelity. A wireless communications network conforming to IEEE 802.11 specifications. More details of Wi-Fi are in issue 82 of Monitor
- Worldwide Interoperability for Microwave Access. Provides wireless data over long distances. More details of Wi-Fi are in issue 110 of Monitor
- Wireless sensor network.
- Conventionally, the horizontal axis of any type of graph.
- Conventionally, the axis perpendicular to and in the horizontal plane through the x-axis of any type of graph.
Wireless communication method commonly used in home automation.
- 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.
Is there a data acquisition term we've missed that you would like explained? Let us know.