The cost of these new bench top multimeters is so attractive
that they seriously challenge the pricing of top-of-the-line hand-held digital
multimeters. Unless portability is a "must have" on your feature list, why would
you buy another handheld? Check out these specs: 5½ digits (120,000 count)
display resolution, 120ppm (.012% + 5 digits) basic DC accuracy and
1μV to 10mV DC
Including the protective holster, the 3146A measures about 255
(W) x 105 (H) x 305mm (D) and weighs slightly less than 3kg.
Measurements include DC voltage and current, true RMS AC &
AC+DC voltage and current, resistance, frequency, diode test and continuity
test. Bandwidth for true RMS voltage measurements is 20Hz to 100kHz. Detailed
specifications are presented in the accompanying panel.
In addition to the basic measurements, a number of useful
arithmetic functions can be applied to many of the readings. For example, when
measuring AC or DC volts, a modifier can be applied to display power in dBm with
respect to a reference impedance. The impedance is selectable in 21 ranges from
2Ω to 8000Ω.
Other functions include "compare", "relative", "minimum",
"maximum" and "hold", many of which can be combined. For example, if "dBm" and
"relative" are selected, the result of the dBm calculation becomes a relative
base for new measurements.
These meters have five input terminals rather than the three
(or four) typically provided on lower performance models. The extra two
terminals are for the "sense" lead connections in a four-wire ("Kelvin")
resistance measurement scheme. Using four leads results in double the accuracy
that can be achieved with just two leads; as high as 0.05% on the
120Ω scale. Of course,
conventional two-wire resistance measurements are also supported.
The bottom sense terminal is also used as the positive terminal
for current measurements on the mA ranges. In addition, this terminal can be
used in conjunction with the main positive and negative terminals to perform
3-wire, simultaneous current and voltage measurements. This could be useful for
measuring power in a circuit or the gain of a transistor, for