Capgo datalogger, data logger, datalogging and data logging.

  

Measurement Glossary

 
 

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

ADC - Analog to Digital Converter - a device for converting a continually variable analog signal into a quantized digital representation of the original signal. There are many techniques for implementing an ADC.

Aliasing - a artifact of a discrete sampling process when the signal being sampled contains frequencies higher that half the sampling frequency. This can lead to misleading data.

Ambient - surrounding or prevailing conditions

Ampere or Amp - the metric unit for electric current

Analog - reference to a measurement or representation of a quantity as a continuum as opposed to digital where there is an implication of quantization

Aperture time - in a sample and hold circuit, the time taken for a sample to begin after the command is given.

B

Backlash - same as hysteresis but more commonly applied to mechanical systems

Baseline - a reference set of data against which operating data is compared.

BCD - Binary Coded Decimal where decimal digits are expressed in a binary code between 0000 (zero) and 1001 (nine)

Bridge - an electronic network that effectively provides zero offsetting. See Wheatstone Bridge

C

Calibrate - to ascertain the relationship between the input and output of a sensor or measuring device.

Chart Recorder - a paper based recording device where the position of a pen or equivalent is controlled by a signal from a sensor.

Color Code - a coding system for identifying a specific type of object within a class of object. See Thermocouple Color Code and Resistor Color Code

Common Mode Rejection Ratio - CMRR - a measure of the ability of a differential input circuit of a measuring device to reject an interfering signal that is common to both the input leads.

Conductivity (electrical) - the property of a water sample to transmit electric current under a set of standard conditions. It is the inverse of resistance and expressed in units of Siemans.

Conversion Time - the time required by an analog to digital converter to fully convert and analog input sample.

Correlation - measurement of the degree similarity between two signals.

Current Loop (4 -20 mA) - An industrial signaling standard between transducers (transmitter) and measuring device (reliever). The signal is scaled between 4 and 20 mA by the transmitter.

D

Dark Current - the current that flows in a photo sensor when there is no incident radiation.

Data Logger - a device that is able to acquire reading from one or more sensors and store the data in a form suitable for later analysis. Many data logger carry out filtering, linearizing and some data reduction.

Decibel - a logarithmic unit for measuring relative strength of a signal.

Differential Amplifier - a device which compares two input signals and amplifies the difference between them.

Drift - an undesired change in output over a period of time that is unrelated to input. Can be due to aging, temperature effects, sensor contamination etc.

Dynamic Range - the range on input signals that a device can accept without introducing significant errors.

Dynamic Response - the behavior of the output of a device with a changing input

E

Eddy Current - an AC current setup near the surface of a conductor exposed to an electromagnetic field

EMC - Electro-Magnetic Conformance - standards associated with the emission of undesired radio frequency energy by devices and the level of susceptibility of a device to similar energy

Encoder (sensor) - a device that converts a linear or rotary displacement into digital representation

Erg - unit of energy in the CGS system of units. 1 erg = 10-7 joules

Excitation - power applied to a sensor to enable it to function

F

Feedback - An important concept in circuit design and control systems where the difference between the output and the desired out (the error signal) is used to help correct the output.

Filter - a circuit or a software program that is able to reduce unwanted noise, thus improving the signal to noise ratio

Floating - a condition where the voltage on a line relative to a reference point is not defined due to the lack of an electrical connection or due to very high source impedance

Frequency Response - a measure of a device's ability to respond to inputs of different frequency, usually expressed as an amplitude vs frequency plot or more simply as the -3db (decibel) frequency limits. Related to time constants

G

Gain - the degree of signal amplification in a system or subsystem expressed as a scalar number or in logarithmic terms as db (decibels).

Galvanometer - an instrument for measuring small electric currents the movement of a current carrying coil in a magnetic field.

Gaussmeter - an instrument for measuring the intensity magnetic fields

Geiger-Muller Counter - a radiation measuring instrument based on a high voltage (200V to 1000V) gas filled tube that detects charged particles using amplification by an avalanche process.

Grey Code - a generic term for a family of binary codes that have the characteristic of changing only one bit in the code where incrementing or decrementing a single number in the code. This is done to overcome the potential ambiguity caused by uncertainty about the precise point when individual bits in a non-Grey code flip due to a change of input.

Ground - a neutral reference for electrical potential, generally the potential of the Earths crust.

Ground Loop - a circular current path that includes at least two nominal grounds. A major cause of problems in the use of sensors and their associated equipment. See the Ground Loop page.

Guard - a shield or screen actively maintained at the common mode voltage of a signal pair with the intention of reducing the effect of insulation leakage and capacitive pick-up on signals with a high source impedance.

H

Hertz - the unit of frequency - cycles per second

HPLC - High Pressure Liquid Chromatograph - an sensitive instrument for identifying large molecule compounds.

Hysteresis - A characteristic of materials, sensors and sometimes instruments to make their behavior dependent on the immediate history to which they have been subjected. Typically the final settling point is different when approached from above to when it is approached from below.

I

Impedance - the complex ratio of a force like parameter to a related velocity like parameter. For example temperature to heat flow, voltage to current, pressure to flow.

Impulse Excitation - A method of measuring the response of a system by applying a short sharp pulse

Indicator - a device to display the value of a parameter

Instrument - a device for measuring the value of an observable parameter. The device may display, record or otherwise process the measurement.

Integrator - a device that mathematically integrates and input. For example and integrator connected to a flow meter will output the volume pasted since last reset

Intrinsic Safety - A protection method for use in potentially explosive atmospheres that limits the energy available to create a spark or heat surfaces

J K

Johnson Noise - thermally induced electrical noise in resistive elements. See the Noise page.

Kalman Filter - a process for estimating the value of parameters in the presence of noise and time delays.

Kelvin - an absolute temperature scale. See the Temperature page

Kelvin Probe - A method for increasing the precision of a measurement by inserting measurement wires at the exact point of interest and there by eliminating the effect of voltage drops along current carrying wires.

L

Leakage - an undesired electric current path from signal wires to ground or other destination. Leakage can introduce significant errors with high impedance sensors.

Linearity - The degree of conformity of the output of a system to a straight line match with the measured parameter.

Low Pass Filter - ideally a filter that passes all frequencies below its cut-off frequency and rejects those above the cut-off. In practice the cut-off characteristics are far from ideal.

M N

Noise - The generally unwanted component of a signal that tends to interfere with the measuring process. The noise can be random or periodic, and often varies in intensity.

Nyquist Rate - defines the minimum sampling rate required to ensure no loss of information. It is twice the highest frequency component in the signal. In practice it needs to be a little higher than this due to imperfect low pass filters.

O

Output Swing - the peak (both positive and negative) output voltage capability of an amplifier with a defined load resistance.

P

Parameter - in the context of sensors, the thing that is being measured

PCB - Printer Circuit Board

PID - Proportional-Integral-Deriverative - refers to a control method where the controlling signal is a function of the error, the error's history and the error's rate of change.

PIN Photodiode - a semiconductor light detecting diode with a particularly fast response time.

Q

Quantization - the subdivision of the range of a reading into a finite number of steps, not necessary equal, each of which is assigned a value. The concept is particularly applicable to analog to digital and digital to analog conversion processes.

Quantum noise - noise due to the discrete or particular nature of light and other short wavelength electromagnetic radiation.

Quartz - a transparent crystalline mineral of silica that finds application in sensors due to its optical and piezoelectric characteristics.

R

Resistor - an electronic component that offers a known resistance to the flow of electricity. See the Resistor Color Code for details on standard values and other information.

RTU - Remote Transmitter Unit - a device accepts data from a range of sensors and telemeters the information to a distant destination for recording and processing. RTUs can also receive instructions and act on them as part of a control loop.

S

SCADA - Supervisory Control and Data Acquisition. A generic architecture for industrial monitoring and control systems, especially those with widely separated stations.

Scale factor - a constant multiplier which converts an instrument reading to a measured value in standard units for the parameter being measured.

Scanner - a switching device that enable a single measuring instrument to sequentially sample multiple sensors.

Schmitt Trigger - an input circuit of a measuring instrument that generated a two state output depending on whether the input is above or below a threshold. The circuit response always includes some hysteresis to improve noise immunity

Sensitivity - the smallest change in a physical quantity or parameter that can be detected by a measuring system.

Sensor - a device that detects the value or the change of value of a physical quantity or parameter and converts the value into a signal for an indicating or recording instrument. Also see Transducer.

Signal Conditioning - the process of interfacing to a sensor, amplifying and filtering its signal ready for display or ADC.

Slew Rate - the maximum rate which an amplifier's output can change, generally expressed in V/µs.

T

Telemetry - The process by which measured quantities from a remote site are transmitted to a data collection point for recording and processing.

Time Constant - The time required to complete 63.2% of the total rise or decay after a step change of input. It is derived from the exponential response e-t/T where t is time and T is the time constant.

Time Series - a sequence of data assigned specific moments in time. It is the history of the object of interest.

Torque - a rotary force

Transducer - a device that converts an input signal of one form into an output signal of another form. Often used interchangeably but not necessarily correctly with sensor. In this work, "sensor" generally refers to the "raw" sensing element which is strictly speaking a transducer, and the term "transducer" is used to describe a sensor with some signal conditioning within the package.

U V

Vibrating Wire Strain Gauge - a device that responds to strain by changing its natural resonant frequency. The wire is electrically plucked and the frequency measured. Alternatively wire can be maintained in continual vibration with appropriated circuits.

Volt - a unit of electromotive force or potential difference

W

Warm-up Period - the time it takes a circuit to stabilize after the application of power.

Watt - the metric unit of power

Wheatstone Bridge - a four arm resistance bridge having 1, 2 or 4 variable resistances. It is commonly used with resistance based sensors, especially strain gauges and RTDs.

Wien Bridge - a type of AC bridge, rarely deployed

X

X-Y Recorder - a paper based recorder that automatically draws a graph of the relationship between variables

Y Z

Zero Suppression - a process used to increase system sensitivity of sensors with a large output offset. The bridge circuit is an example.