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Analog Bar Graph A digital
display that simulates the movement of the needle of a mechanical
(analog) meter.
Autopolarity Automatic (+)
or (-) indication for a DC voltage or current.
Autoranging Automatic selection
of range that will give the best resolution.
Bandwidth Range of frequencies
over which AC voltages are generated (range of
frequency over which an instrument provides accurate readings).
Clamp-on Type of meter or
adaptor that fits around a conductor to measure AC or DC current
without breaking the circuit.
Conductance A measure of
how easily a substance passes an electrical current; the
reciprocal of resistance; conductance = 1/resistance; measured
in siemens.
Current Probe An accessory
to a multimeter or oscilloscope that allows reading and
display of current without breaking the circuit (see Clamp-on).
Decibel Ratio of two power
levels [DB = 10 log (p1/p2)].
Diode Test Range A low power
test range that allows a DMM to measure components in a circuit
without damage, or to measure the forward bias in diode junctions.
Frequency Counter A device
that measures the number of cycles of an AC signal with respect
to time.
Function Generators Used
in research, design, and service applications to produce a
variety of high quality waveforms over a wide frequency range.
Applications include audio
and video equipment tests, frequency response testing, evaluation
of digital timing, as well as time domain analysis of amplifiers
and comparators. Key parameters include frequency and amplitude
range, sine wave distortion and types of waveforms produced such
as sine, square, triangle and pulse.
Ground Fault Interrupter (GFI) A
safety device that disconnects power from a circuit when a potentially
dangerous electrical condition exists. A GFI protects people
while fuses or circuit breakers protect equipment.
Halogen Gas A gas containing
chlorine, fluorine or bromine; these are usually Freon
refrigerants.
Input Impedance Opposition
to current flow through a test instrument, measured in
ohms; a high value means less disturbance to the circuit being
tested.
Liquid Crystal Display (LCD)
Digital display that uses very little power and has high
contrast.
Megohmeter Insulation tester;
an ohmmeter capable of measuring very high resistance
(over 1,000 meghoms).
Multimeters Measure voltage,
current, and resistance. Two types: analog and digital.
Both are available in bench or handheld models. Analog Meters
have a mechanical method of displaying the applied signal which
is better for observing changes, adjusting for peak or dip, and
for instantaneous response. Digital Meters give a visual indication
which is represented as a discrete number that provides greater
accuracy.
Key parameters of multimeters are:
Voltage, current, and resistance ranges; number of digits displayed
(digital only); resolution, and accuracy. Functions available:
DC and AC voltage, resistance, conductance, DC and AC current,
diode check, frequency, temperature, and data hold.
Oscilloscopes Create a pictorial
representation of varying voltages as related to time.
They allow for the observation of waveform distortions, amplitude
changes, frequency or
period (time) changes, and phase changes.
Key parameters of oscilloscopes are:
Accelerating Voltage is the internal voltage that causes illumination
of the screen. In
general a higher voltage provides a brighter display for a given
sweep speed.
Bandwidth is the range of frequencies that can pas through the
oscilloscope's internal
circuitry with minimum attenuation and degradation. Channels
are input circuits where the observed signal is applied. Multiple
channel capability allows simultaneous measurement of two or
more separate input signals. Rise Time is the time required for
an observed waveform to rise from 10 to 90% of its maximum amplitude.
Typically measured in nanoseconds. Sensitivity is the minimum
voltages that will give a one division deflection.
Pyrometer An electronic device
that can measure a wide range of temperature (typically - 100
to 1999°F); especially high temperatures.
Resolution The magnitude
of an input signal equal to one digit change in the least
significant digit in the display. Smallest value an instrument
can measure.
Sleep Mode When an instrument
turns off by itself when not in use; this conserves
battery life.
Thermistor A resistor that
is sensitive to temperature changes. It will change in
resistance as a function of changing temperature.
Thermocouple Converts (heat)
into a low level DC voltage to measure temperature.
True RMS Capability to accurately
measure the value of AC voltage and current having
non-sinusoidal waveforms as well as sinusoidal waveforms.
Volt-Amperes A representation
of apparent power in an AC circuit.
Watt A unit of electrical
power measuring the rate at which energy is converted to work
or dissipated as heat.
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TEST INSTRUMENTS
TERMINOLOGY