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Test Equipment Glossary
- Active Power
A power measurement that multiplies the voltage portion of the signal being measured by
the current that is in phase with that voltage.
- Analog output
A signal generated from a meter, for example, which can drive a recorder, an external
display, or a controlling device such as a heater, motor, etc. Analog signals used for such purposes are
typically 4-20mA , 1-5Vdc, or similar ranges.
- Apparent Power
A term only applicable to Alternating Current (AC) circuits, it is the product of the
voltage applied times the current flow. The unit of measure is VA, or Voltamperes.
Auto hold - The ability of a measuring device to wait until a reading has stabilized before holding (storing)
that reading on the display.
- Auto-ranging
Ability of a measuring device to automatically select the appropriate range of
measurement.
- Cold Junction Compensation
Circuit in a measuring device which resolves the difference between
an ambient temperature reference (used when device was calibrated) and the actual operating temperature
of the measuring device.
- Conductance
The reciprocal of resistance expressed in term of Siemans (formally mhos)
- Continuity beeper
Audible tone emitted from a meter when resistance measured falls below a
threshold level (typically 20-50W).
- Cosine F
Voltage and Current sometimes do not happen together, often there is a difference. The
difference is an angle, F, a value between 0 and 90. The greater the angle, the bigger the difference
between True and Apparent Power, the smaller the Power Factor. If Voltage and Current happen at about
the same time, F is small, the values of True and Apparent Power are close, Power Factor approaches 1.
- Criterion Sound Level
The eight hour average weighted sound level, expressed in dB, that
corresponds to the maximum permitted daily exposure to noise as prescribed in national and state
regulations.
- Data Acquisition
The ability of an instrument to communicate measurement information as it occurs.
The meter must be in communication with a computer for measurement storage to occur.
- Datalogging
The ability of a meter to store measurement information "on board" in nonvolatile memory
until such time it can be downloaded to a computer for storage, analysis and report generation.
- Data hold
Function of a measuring device which holds a displayed value when a user presses a key or
button.
- dB: - Decibels
The unit of measure used when measuring the level of sound. Every 3dB represents
approximately double (-3dB = 1/2) the power or sound level, ie: 53dB is twice as loud as 50dB.
- dBm
Decibels above one milliwatt. A measure of power equal to 10 times the common logarithm of the
ratio of a given power to 0.001 watt
- Differential
In dual input measuring devices, the differential is the displayed difference between the two
inputs. (Input A - Input B = Differential).
- Diode check
Function of a measuring device which analyzes the operation of a diode. The two leads
of the diode are inserted into the device and the user is alerted visually and/or audibly as to the diode's
integrity.
- Display counts
The number of display units a meter or other device can indicate. For example, a
3-1/2 digit display can indicate from 0 - 1,999 (which is 2000 counts); a 4-1/2 digit display can indicate from
0 - 19,999; a 3-3/4 digit display can indicate from 0 - 3,999 counts, etc. If a meter is "bi-polar" it can
indicate positive and negative units depending on the polarity of the signal being monitored. For example, 0
- ±1999.
- Duty Cycle
The ratio of the working time to the total time of a pulse train expressed as a percent.
- Elapsed Time
The period of time between the start of a measurement series to the last measurement
observed or recorded.
- Electric Power
Is the rate at which electricity does work. More work done in a set time, or the same
work done in a shorter time, both require more electrical power. The unit of measure for electric power is the
Watt . Electric power, measured in Watts is also known as True Power.
- Emissivity
A term related to temperature measurement using Infrared radiation. Errors in IR
measurements can occur based on the color, shape and presence of reflection on the measurement
surface. A wide emissivity adjustment should be available on an IR thermometer to allow the user to
compensate for these types of errors.
- EMF/Electromagnetic radiation
Waves generated by a magnet configuration which consists of a
coil wound around a steel core. The core is strongly magnetized when current flows through the coil. Video
monitors, power lines, and wire harnesses are a few devices which produce electromagnetic radiation.
- Exchange Rate
(also Doubling Rate) Refers to the rate in which sound energy is averaged over time.
Every time the sound energy doubles, the measured level increases by 3dB ,which most of the world uses.
In the U.S., OSHA uses a 5dB exchange rate.
- GO/NO GO Alarm
An output from a meter or controller which is used to indicate when a preset
measurement point has been reached or exceeded. The alam may be visable, audible, electrical or any
combination of these.
- Kelvin Connection
A four wire method of connecting test leads which is designed to eliminate or
greatly reduce the effect of lead or contact resistance and thus permitting accurate measurements of low
resistance.
- LCD
Acronym for Liquid Crystal Display. Liquid crystal is a liquid that is not isotropic, that is, it forms
patterns when polarized. The orientation of the molecules of the liquid are arranged by the meter to form the
display.
- LED
Acronym for Light Emitting Diode, a very common display type. An electrical current is passed
through the diode causing illumination aided by the colored lens which surrounds them. LEDs usually have
7 light segments per digit when used as an alpha-numeric display. Also commonly used to indicate
ON/OFF or status functions individually. Orange-red, green, and yellow are common LED colors.
- Load
A device that is driven by the output of a meter or other measuring/controlling device. An example
of a load is a resistor being measured by a multimeter. The resister "loads" the meter since it becomes part
of the measuring circuit.
- Microprocessor
Integrated circuits which perform many instructions per second (mathematical
equations, calibration data storage, display updates, etc.) precisely and quickly. Microprocessors are at
the heart of computer accuracy, repeatability, and speed, providing similar attributes to electronic measuring
devices such as calibrators, multimeters, thermometers, etc.
- Min/max
A function of a measuring device which records (saves) the highest and lowest reading it has
encountered since being reset (cleared) or powered up.
- Multiplexer
A device that sequences access to a communcation port. Severl different devices can
share a single COM port on a computer if they are multiplexed.
- Noise Dose
A measure of the exposure to noise expressed as a percentage of a maximum permissible
exposure. The maximum permissible exposure (or 100%) is prescribed in national or state regulations.
- Overload
A signal that is greater than that which a measuring device can accurately or safely accept.
Many meters have overload protection in the form of a fuse, or similar device, to protect the meter from such
a signal.
- Over range indication
Visual display alerting the user that the signal present at the meter's input is
out of range.
- Peak hold
The ability of a measuring device to hold the highest reading until the user clears the display.
Also known as Peak Detect.
- Power Factor
is the ratio of Watts to VA, or True Power divided by Apparent Power. This can be
expressed as a decimal or percentage, i.e.: PF=0.75 or PF=75%. True Power is never greater than
Apparent Power, so the Power Factor is never greater than 1. Power Factor may also be expressed as
Cosine F where F is an angle between 0 and 90.
- Psychrometers (Wet Bulb)
A relative humidity measuring device which has two thermometers.
One measures ambient temperature (dry bulb), the second measures the temperature of an element
surrounded by a fibrous material saturated with water (wet bulb). Reference tables are then used to
determine relative humidity.
- Resolution
The smallest value a display device can indicate. For example, if a device can display 0.0
to 100.0 RPM, the smallest measurement and, therefore, the resolution is 0.1 RPM.
- Response time
The rate at which a measuring device responds to a change in the measured variable.
- RH Capacitance Probe
Capacitive device that senses relative humidity. The meter used with such
a probe senses the change in capacitance based on the moisture encountered by the capacitor's dielectric
and displays the relative humidity based on this capacitance value.
- RH Resistance Probe
Resistive device that senses relative humidity. The meter used with such a
device monitors the resistance of the probe which changes proportionately to the amount of moisture
encountered. The meter then displays the relative humidity based on this resistive value.
- RTD
A temperature measurement device whose resistance is proportional to temperature. 2,3, and 4
wire RTDs are available.
- Single Phase
A good example of a single phase power source is a typical AC wall outlet. This is
considered to be single phase because there is a single alternating voltage/current available. Three-phase
on the other hand, provides three separate alternating signals.
Thermistor
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