4-Wire resistance measurement

A way to measure the values of a resistor while avoiding errors caused by the wire runs. Two wires carry a current to the resistor, and two wires measure the voltage generated. Commonly used with resistance temperature detectors (RTDs).



Absolute pressure sensor

A sensor that measures the input pressure in relation to zero pressure (a total vacuum on one side of the diaphragm).


The rate of change of velocity. Acceleration has two characteristics: magnitude and direction.


The degree of conformity of a measured or calculated value to its definition or with respect to a standard reference (see uncertainty). (2) The maximum error of a measured value with respect to its true theoretical value.

Acquisition time

The time required for the front end of a DAQ board to capture an input signal and hold it to within a specified error band after a sample command is received.


Analog-to-digital converter–An electronic device, often an integrated circuit that converts an analog voltage to a digital number.


A well-defined procedure that transforms one or more given input variables into one or more output variables in finite numbers of steps.

Analog-to-digital (A/D) conversion

The process of converting a continuous analog signal to a digital value that represents that signal at the instant at which it was sampled.


Application-Specific Integrated Circuit–A proprietary semiconductor component designed and manufactured to perform a set of specific functions for a specific customer.


Hardware–A property of an event that occurs at an arbitrary time, without synchronization to a reference clock. (2) Software–A property of a function that begins an operation and returns prior to the completion or termination of the operation.

Asynchronous communications

Communications protocols in which data are transmitted at arbitrary points in time. Most commonly used to refer to serial data transmission protocols such as RS-232 or RS-485.

Background acquisition

Data is acquired by a DAQ system while another program or processing routine is running without apparent interruption.


A sensor that either detects a biological substance or incorporates biological materials to accomplish sensing.


A test during which known values of a measurand are applied to the device under test and corresponding output readings are recorded under specified conditions.


Controller Area Network–A serial bus that finds increasing use as a devicelevel network for industrial automation. CAN was developed by Bosch to address the needs of in-vehicle automotive communications.

Capacitive touch

Capacitive touch gets its name from the electrical distortion that results in the screen's capacitive field when impressed upon by body capacitance, or the physical property of the human body that enables it to act as an electrical capacitor, or conductor of electric charges.


The technique of modifying data from a source to correct the influence of additional environmental effects.

Conversion rate

The speed of a data acquisition system expressed in a number of conversions or samples per second.

Conversion time

The time required, in an analog input or output system, from the moment a channel is interrogated (like in a read instruction) to the moment that accurate data are available.


A circuit that counts external pulses or clock pulses (timing) and can either operate as an event counter or measure the time between two events.




Digital-to-analog converter–An electronic device, often an integrated circuit that converts a digital number into a corresponding analog voltage or current.

Data acquisition board

A data acquisition system incorporated on a PCB that is electrically and mechanically compatible with a particular computer system.

Data acquisition system

A system that processes one or more analog or quasi-digital signals and converts them into a digital form for the use by a computer system.

Data logger

A data acquisition system that incorporates a small computer, is typically portable, and is intended to collect data autonomously for extended periods of time. The data are afterwards downloaded into another computer for processing and analysis.

Differential pressure sensor

A sensor, which is designed to accept simultaneously two independent pressure sources. The output is proportional to the pressure difference between the two sources.

Digital output

Output that is of only two stable states, appearing in the manner of a switch; that is, it is either On or Off or High or Low (i.e., high voltage or low voltage).

Digital-to-analog (D/A) conversion

The process of converting a digital signal or a code into an analog or quasi-digital signal.

Digital-to-analog converter (DAC)

A device that converts a digital value or code into an analog or quasi-digital signal.

Discrete Fourier transform

A version of the Fourier transform that operates on data that have been sampled at discrete, uniformly spaced points in time.


Direct Memory Access–A method by which data can be transferred to/from a computer memory from/to a device or memory on the bus while the processor does something else. A DMA is the fastest method of transferring data to/from a computer memory.

Drift (frequency)

The linear (first-order) component of a systematic change in frequency of an oscillator over time. Drift occurs due to ageing plus changes in the environment and other factors external to the oscillator.


(Digital signal processing)–(1) the science concerned with representation of signals by sequences of numbers and the subsequent processing of these number sequences. (2) Techniques for modifying and analysing a signal after it has been sampled and converted into the digital domain by an ADC.

Dynamic error

The error which occurs because the sensor’s output does not precisely follow the variations in time of the measurand.

Dynamic range

The ratio of the largest signal a system can handle to the smallest signal it can reliably resolve. A dynamic range is typically expressed in decibels for analog systems and bits (N) for digital systems, where dB = 6.02 N = 20 log (the largest signal/the smallest signal resolved).


A device that converts the linear or rotary displacement into digital or pulse signals. The most popular type of encoder is the optical encoder, which uses a rotating disk with alternating opaque areas, a light source and a photodetector.


The difference of a measured value from its known true or correct value (or sometimes from its predicted value).

Fourier transform

A mathematical technique that transforms a continuous function from its time-domain representation to its frequency-domain representation. The discrete Fourier transform performs the analogous function on discretely sampled data.


The rate at which a periodic phenomenon occurs over time.

Frequency deviation

The difference between frequency values of the same signal at two different times or the difference between the instantaneous signal frequency and the average signal frequency.

Frequency difference

Difference between the frequencies of two different signals.

Frequency output

An output in the form of frequency, which varies as a function of the applied measurand.

Full scale (FS)

The maximum specified range of a data acquisition system.

Full-scale range (FSR)

The difference between minimum and maximum allowable input or output values for a data acquisition system.

General-Purpose Interface Bus (GPIB)

IEEE-488 standard interface connecting peripheral devices, often sensors and programmable instruments, to a computer.

GUI—graphical user interface

An intuitive, easy-to-use means of communicating information to and from a computer program by means of graphical screen displays. GUIs can resemble front panels of instruments or other objects associated with a computer program.

Hall effect

When a semiconductor, through which a current is flowing, is placed in a magnetic field, a difference in potential (voltage) is generated between the two opposed edges of the conductor in the direction mutually perpendicular to both the field and the conductor. Typically used in sensing magnetic fields.


The measure of a sensor’s ability to represent changes in the input parameter, regardless of whether the input is increasing or decreasing.

Integrated circuit (IC)

An interconnected array of active and passive elements integrated within a single semiconductor substrate or other compatible material, and capable of performing one complete electronic function.

Integrating ADC

An ADC in which the input voltage is integrated over time. Different types of ADCs include a single slope, a duel slope, a quad slope, and a charge balancing.

Intelligent sensor

See smart sensor


A common boundary between electronic systems, or parts of a single system.

Interface circuit

A circuit that links one type of a device with another. Its function is to produce the required current and voltage levels for the next stage of the circuitry from the previous stage.

Linearity (linearity error)

The deviation of the sensor output curve from a specified straight line. A linearity error is usually expressed as a percent of the full-scale output.


The process of modifying a signal, either analog or digital, to compensate for the nonlinearities present in the source or previous signal processing.


A physical quantity, property or condition, which is measured (e.g., pressure, acceleration).


An IC chip that provides sensing and/or actuation functions in addition to electronic ones.

Modulating Sensor

See parametric sensor.


An output signal of the random amplitude and random frequency not present in the measurand.


The difference between the realized value and the reference value.

Parametric (modulating) sensor

A device producing the primary information by way of respective alterations of any electrical parameters of some electrical circuit (inductance, capacity, resistance, etc.), the measuring of which it is necessary to have an external auxiliary power supply. Examples of such types of sensors are pressure sensors based on the piezoresistive effect and photodetectors based onthe photoelectric effect. Sometimes the modulating sensor is called the ‘passive’ sensor.

PCM (Program-oriented conversion method)

The processor algorithm of measurement, incarnated in the functional-logic structure of a computer or a microcontroller through the software.

Piezoelectric effect

The property of certain materials that allows them to develop a voltage when deformed by stress, or to become strained when subjected to the application of a voltage.

Piezoresistive effect

The property of a resistor that produces a change in resistance in response to the applied strain.

PIR - Passive Infrared Sensor

A passive infrared sensor is an electronic sensor that measures infrared (IR) light radiating from objects in its field of view. They are most often used in PIR-based motion detectors.


The degree of mutual agreement among a series of individual measurements. Precision is often, but not necessarily, expressed by the standard deviation of measurements.

Pressure sensor

A device that converts an input pressure into an electrical output.

Proximity sensor

A device that detects the presence of an object without physical contact. Most proximity sensors provide a digital on/off relay or a digital output signal.


Pulse-width modulation–Generation of a pulse waveform with a fixed frequency and variable pulse width (the duty-cycle). PWM is used to control discrete devices such as DC motors and heaters by varying the pulse width (the ratio of on time to off time).

Quantization error

The inherent uncertainty in digitizing an analog value due to the finite resolution of the conversion process.

Quasi-digital sensor

The discrete frequency-time domain sensor with the frequency, the period, the duty-cycle, the time interval, the pulse number or the phase shift output.

Radar for presence detection

The microwave technology is based on the so-called Doppler effect. The radar sensor emits (via its emitter TX) continuously microwaves with a specified constant frequency within a predefined field. Any object (including persons) within the detection field will reflect back the microwave to the sensor; the receiver RX will “catch” this reflected wave.


The measurand values over which the sensor is intended to measure, specified by the upper and lower limits.

Real-time processing

A procedure in which results of an acquired and computed value can be used to control a related physical process in real time.


A stable source for a physical quantity, such as voltage, frequency, etc. used in a measuring device to maintain measurement stability and repeatability.

Relative accuracy

A measure in LSB of the accuracy of an ADC. It includes all nonlinearity and quantization errors. It does not include offset and gain errors of the circuitry feeding the ADC.


The measure of a sensor’s ability to maintain both accuracy and precision under conditions for which it is designed to perform for the expected life of the device.


The smallest significant difference that can be measured with a given instrument. Resolution can be expressed in bits, in proportions, or in a percent of a full scale. For example, a system has a 12-bit resolution, one part in 4.096 resolution, and 0.0244 percent of a full scale; a measurement made with a time interval counter might have a resolution of 10 ns.

Response time

The time needed for a sensor to register a change (within a tolerance of an error) in the parameter it is measuring.


A property of a sensor that has an extremely stable reference and calibrates its own ADC without manual adjustments by the user.

Self-generating sensor

The device permitting to receive a signal immediately by the way of a current i(t) or voltage V (t) and which does not require any source of power other than the signal being measured. Examples of such types of sensors are Seebeck-effect based thermocouples and photo-effect based solar cells. Selfgenerating sensors are also called ‘active’ sensors.

Sensing element

That part of a sensor which responds directly to changes in the input pressure.


The minimum change in the parameter being measured that will produce a detectable change in a sensor’s output.

Signal conditioning

The processing of the form or mode of a signal so as to make it intelligible to or compatible with a given device, including such manipulation as pulse shaping, pulse clipping, digitizing and linearizing.

Smart sensor

One chip, without external components, including the sensing, interfacing, signal processing and intelligence (self-testing, self-identification or selfadaptation) functions.


Simultaneous Sampling–A property of a system in which each input or output channel is digitized or updated at the same instant.

Strain guage

A piezoresistive sensing device providing a change in the electrical resistance proportional to the level of the applied stress.


Transmission–via radio waves, wires, etc.–of the instrument reading across distances. Also called telemetering or remote metering.


A device that measures temperature-induced changes in resistance of a resistor or a semiconductor.


A temperature-measuring device made of two dissimilar conductors joined together at their ends. The unit generates the thermoelectric voltage between the junctions that represents their temperature difference.


A fully packaged, signal-conditioned, compensated and calibrated sensor.

Transfer function

The input-to-output response characteristics of a device.


A device that converts the output of a sensor into a form more suitable for communication to another system.


Limits of the confidence interval of a measured or calculated quantity. Note: The probability of the confidence limits should be specified, preferably as one standard deviation.

Virtual instrument

A measuring instrument composed of a general-purpose computer equipped with cost-effective measurement hardware blocks (internal and/or external) and software, that performs functions of a traditional instrument determined both by the hardware and the software, and operated by means of specialized graphics on a computer screen. The necessary condition of a virtual instrument existing is the software realization of the user interface, performed by a general-purpose computer and the sufficient condition is that a hardware and a software part of the virtual instrument do not exist separately as an instrument.

Voltage-to-frequency converter (VFC)

A device that converts an input voltage into a periodic waveform output with the frequency proportional to the input voltage.

Wiegand-effect sensor

The generation of an electrical pulse in a coil wrapped around or located near a Wiegand (a specially processed ferromagnetic) wire that is subjected to a changing magnetic field. The effect is proprietary and patented.