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GENERAL
INFOHMATION
1.4 MANUAL
ADDENDA
Information
concerning
improvements
or changes to the
instrument
which occur after this manual is printed will
be found on an addendum sheet included with the instru-
ment.
Please
be
sure that
you read this information
before
attempting
to operate or service your instrument.
1.5 SAFETY SYMBOLS
AND TERMS
The following
safety terms and symbols are used in this
manual or found on the instrument.
The A
symbol on the instrument
indicates that the user
should refer to
the
operating instructions
in this manual
for further
details.
The WARNING
heading as used in this manual explains
dangers that could result in personal
injury
or death.
Always
read the associated information
very carefully
before performing
the indicated
procedure.
The CAUTION
heading
used in this manual
explains
hazards that could damage the instrument.
Such damage
may invalidate
the warranty.
1.6 SPECIFICATIONS
Detailed Model 194 specifications
are located at the front
of this manual. Some terms used in the specifications
are
discussed in the following
paragraphs.
1.6.1 Resolution
The resolution
of an A/D converter is generally
defined
as the number
of output
states expressed in bits. The
number of output states of a binary quantizing
A/D con-
verter is Zn, where n represents the number of bits. The
AID converter in the Model 394 operates with either a-bit
or 16.bit resolution, depending on the sampling rate. Thus,
the AID converter has either 256 (28) or 65,536 (216) output
states.
The resolution
figures given in the specifications
are de-
rived by dividing
the full scale displayable
range by the
number of steps for that particular
converter resolution.
For example, in the lh-bit mode, the 32OmV range is ac-
tually capable of displaying
values in the range of -327.68
to + 32.7.67mV, for a total range of 655.35mV. Dividing
this
figure by the total number
of quantized
steps (65,535)
yields the 1OpV resolution figure given in the specifications.
1.6.2 Differential
Non-Linearity
The differential non-linearity
specification defines the max-
imum deviation
of a quantized
step width from the ideal
quantization
step width, FSRI(Z"-l),
where FSR is the full
scale range of the A/D converter (1OV) and n is the number
of bits (8 or 16) depending
on the sampling
rate.
1.6.3 Slew Rate
The slew rate specification
applies to the sample and hold
portion of the A/D converter and is usually defined as the
maximum
rate at which a capacitor can charge expressed
in volts per microsecond.
Generally, it is desirable to have
as high a slew rate as possible in order to minimize
response time.
1.6.4 Input Impedance
and Coupling
The input impedance is simply the equivalent
resistance
appearing between input high and input low shunted by
(in parallel with) the stated capacitance value. Figure 1-l
shows an equivalent circuit of the input impedance appear-
ing at the VOLTAGE INPUT jack. Input impedance can
become especially
important
when measuring
voltage
sources with high internal resistance: the resistive com-
ponent can load the source, degrading measurement
ac-
curacy, and the capacitive element can increase response
time to rapidly-changing
signals
Figure l-l. Equivalent Input Impedance
I-2
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