Fluke 179 Fluke Precision Multimeters - Understanding Specifications for Preci
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- Fluke 179 | Fluke Precision Multimeters - Understanding Specifications for Preci - Page 1
specifications for precision multimeters Application Note Digital multimeters are the workhorses of the electronics industry. Almost all of the electronic products we use in our personal and professional lives are built or serviced using multimeters. Different DMM applications require different - Fluke 179 | Fluke Precision Multimeters - Understanding Specifications for Preci - Page 2
display likely to be to the actual input to the meter?" Meter manufacturers bet their reputations on how a large population of instruments is going to behave for the duration of calibration cycle. (A typical calibration cycle is one year.) Instrument engineers and metrologists use laboratory testing - Fluke 179 | Fluke Precision Multimeters - Understanding Specifications for Preci - Page 3
include the uncertainty of the calibrator in the DMM uncertainty specs. If you see an uncertainty listed as "relative" this means the uncertainty in the calibrator output has not been considered and it must be added to the DMM uncertainty. Elements of digital multimeter specifications Among the many - Fluke 179 | Fluke Precision Multimeters - Understanding Specifications for Preci - Page 4
of test procedures along with applicable limits. Adding all of the limits would render the DMM specifications too cumbersome, so DMM designers just list the standards with which the DMM complies. 4 Fluke Corporation Understanding specifications for precision multimeters Comparing different digital
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Application Note
From the Fluke Digital Library @ www.fluke.com/library
Understanding specifications
for precision multimeters
Digital multimeters are the workhorses of the
electronics industry. Almost all of the electronic
products we use in our personal and professional
lives are built or serviced using multimeters.
Different DMM applications require differ-
ent degrees of attention to specs. A technician
checking a logic power supply can use his trusty
bench DMM confidently to verify that the supply
is within a few percent of 5 V. However, when
the job requires testing critical circuits, checking
precision components, making fine adjustments
in production, verifying compliance with industry
standards, or taking measurements outside the
controlled environment of the lab, then you’ll need
to evaluate specifications carefully.
A solid understanding of specifications is critical
when you’re evaluating the suitability of DMMs
for an application, or when you must be confident
that your readings accurately reflect reality. This
application note discusses some of the thinking
behind DMM specifications and spec sheets. It
defines the various elements of DMM specs and
gives tips on how to apply them.
Specifications and the
spec sheet
Whenever we take a measure-
ment with any meter, we’re
gambling. We’re gambling that
the instrument is going to give us
the “real” reading. Fortunately,
it’s a very safe bet that a quality
multimeter will deliver readings
that coincide with reality. Specifi-
cations quantify the confidence of
getting accurate readings and the
risk of seeing inaccurate readings.
A specifications document is
a clearly written description of
an instrument’s performance.
It should quantify an instru-
ment’s capabilities objectively
under well-defined operating
conditions.
From this formal definition we
can draw the characteristics of
good specifications:
•
Completeness – any factor
that impacts uncertainty is
covered, including operat-
ing limits such as humidity,
altitude, or vibration
•
Clarity – all efforts should be
made to make the specifica-
tions straightforward
•
Objectivity – does not attempt
to mislead for the sake of
promotion
A well-written specification
should maintain the same level
of integrity as a medical chart or
bank statement. Manufacturers
must stand firmly behind their
specs and you should fully expect
that the information you are
getting is accurate and complete.
On the spec sheet, you should
see measurement uncertainty
specs and modifiers that affect
the uncertainty. You will also see
operating limits that constrain
the environment in which the
uncertainty specifications will
hold true. These are stated in
numerical values (e.g. humidity)
or with reference to international
standards (shock and vibration).
First let’s take a closer look at
how we quantify measurement
uncertainty.