signal anal yzers - Helmut Singer Elektronik

With compliments
Helmut Singer Elektronik
www.helmut-singer.de [email protected]
fon +49 241 155 315
fax +49 241 152 066
Feldchen 16-24 D-52070 Aachen Germany
SIGNAL ANAL YZERS
Dual-Channel,
Model 3582A
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DynamicSignal Analyzer 0.02 Hz to 25.5 kHz
Transfer function magnitude end phase measurements
Coherence function measurement
Phase spectrum measurement
Transient capture end frequency domain analysis
De.crtptlon
Tbe 3582A is a powerful dual-cbannel,real-time spcctrum analyzer
tbat solvesbencb or systemsmeasurementproblems in tbe frequency
range of 0.02 Hz to 25.599 kHz. Sophisticated LSI digital filtering
combined witb microcomputer execution of tbe Fast Fourier Transform (FFT) provides exceptional measurementcapability and performance,
Exceptlonal
Frequency Resolution
Tbe ability to resolve closely spacedspcctral componcnts is orten
critical in tbe study of subtle pbcnomenasucb as structural transfer
functions. Unlike conventionaldynamit signal analysis whicb extends
from DC to somemaximum frequency, thc Model 3582A'can "zoom
in" to analyze any selcctedband of frequcncics witb dramatically improved resolution, Tbc start or center frequcncy of tbe 5 Hz to 25 kHz
band analysis spanscan be adjusted in I Hz incrcments to cover tbc
entire frequency range of tbc instrument. Tbis provides resolution
down to 20 milliHertz acrosstbc cntire range tor spectrum analysis or
40 milliHertz tor transfer functions, representingas mucb as 5000 to
I improvemcnt ovcr convcntionaJ"baseband" analysis,
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.
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InternaI periodic and random noise source
Band selectable analysis tor 0.02 Hz resolution
Alphanumeric CAT annotation and marker readout
Exce"ent Low Frequency Cover.ge
Many elcctrical and physical mcasurementshave signficant spectrat information in tbc audio and sub-audio range. With frequency
ranges from 2S kHz down to 1 Hz full scale, tbc Model 3S82A is
extremely weil suitcd to thcsc ty~ of mcasurements.The display
shown in fig. I reprcscnts the phase noise of a freqUCDCY
synthesizer
over tbc range of 0 to 1 Hz with a frequency ~Iution
of 6 milliHertz.
Real Time Mea.urement
Speed
Long measurement times can be a major limitation of swept low
frequency spectrum analyzers. In high volume testing or in applications requiring substantial on-line tuning these long measurement
times are both expensiveand inconvenient. Since the Model 3S82A
usesan advancedmicrocomputer to execute the Fast Fourier Transform (FfT), it can perform equivalent measurementsas much as one
to two orders of magnitude raster than a swept analyzer.
Wlde Amplitude Range
When examining the sensitivity of an analyzer, it is important to
consider the full range of potential applications. If the analyzer does
not directly cover the range of anticipated signals, extemal ampiifiers
or attenuators will be required. Thesedevicescan add their own noise
andcandistort the signalbeingmeasured.
The Model 3S82A offers
150 dB of calibrated measurement range covering +30 dBV (31.6
volts) to -120 dBV (I Jlvolt) and thus minimizes the needfot external
signal conditioning. Even with input sensitivities down to -120 dBV
the input circuit is fully protected against accidental overloadsof 100
Volts DC or 120Volts RMS fOTshort periods.
Wlde Dynamlc Range
In many applications the information of interest is contained not in
the high amplitude fundamental, hut rather in the low amplitude
components.For a spectTumanalyzer to provide useful information
about theselow level components in the presenceof a \arge signal, it
mustoffer widedynamicrange.The Model 3S82Adynamit rangeis
specified as 70 da.
Phase Spectrum MeaBurement
M~t spectrum analyzerscan measureonly tb.eamplitude SpectfU.m
of a signal, yet complete characterization in tbe frequency domalß.
also requires phase information. Signals with identical amplitude
spectra. but different phase spectra can differ significantly. The advanceddigital signal processingtechniques incorporated in the Model
3S82A providedirect measurement
of phasespectra.
Tranal.nt Captur. and Analysis
Many signals such as mechanical shocks and electrical transients
may occur infrequently and spontaneously aod may last only fot a
brief period of time. Swept spectrum analyzers generally cannot handle thesetransient signals. By using digital processingtechniques.the
Model 3S82A can capturo and analyze transients as short as a lew
milliseconds. Tbis means that spectrum analysis and transfer function analysis are no Ionger lirnited to stable. time invariant signals.
Fig.
2A
Fig.
28
Figur.. 2A & 28: Capture and anaiyze transients in both amplj.
lude and pha8e.
Transfer Functlon Measurement Wlth the Internal Noise
Source
Many elcctrical circuitsand mechanicalsystems
canbe treatedas
linear networks and can be characterized by tbc magnitude and phase
of their transfer functions.
Most spcctrum analyzers can mcasurc only tbc magnitude portion
of tbc transfer function - and even then only by assuminga tlat drive
signal. Tbe Model 3582A dircctly mcasures tbc complete transfer
function, both maanitude and phase. With dual channels thc actual
drive signal is mcasured on Channel A and thus docs not have to be
totally tlat; drive signal variations are taken out in the computation
processto give valid results. Tbe major constraint on tbc input signal
is that, unlikea sweptsource,it muststimulateall frequencies
of interest simultancously. Two sourccsare provided in the Model 3S82A
which mcct this constraint. Tbey are pscudo-random and random
noisc. For linear networks, the pseudo-rand&mnoisc sourcegives you
accurate results in tbc fastest thcoretically possibletime. When nonlinearities are a problem, random noisc gives the best estimate of tbc
transfer function at tbc operating point. In addition, both noise
sources are bandlimited to concentrate all stimulus energy in the
band of frequenciesanalyzed. This minimizes test time becauscit improves tbc signal to noisc ratio of tbc measurements.This also minimizes the disturbance to the network under test, which can be very
important in control applications.
With this drive signal functioning as a "tracking generator" substitute, the Model 3582A is a low frequency network analyzer with
"real-time" measurement speed. As with spectrum measurements,
portions of the transfer function as narrow as 5 Hz can be examined
anywhere over the 25 kHz frequency range.
Coherence Functlon Measurement
The measurement of a device transfer function assumesthat the
device under test is linear and that no portion of the output is caused
by noise or extraneous signal sourccs. In active electronic circuits or
mechanical structures these conditions can easily be violated - yet
such violations arevery difficult to identify. The Model 3582A considerably simplifies this problem by providing the direct measurement of the coherence function. This is a frequency domain measure
of the fraction of the power in one signal (e.g., the output) causedby
the other measuredsignal (e.g., the input). If this fraction is 1.0, the
output at that frequency is causedby the input and thc transfer function is valid. If the fraction is near 0.0. the output ia causedby something other than the measuredinput. This causecould be noise, nonlinearities or an unanticipated input, but the result is the same - the
transfer function data at that frequency is suspect.
In addition to serving as a valuable check on the validity of transfer
functions, the coherence function can be useful when investigating
causejeffect relationships particularly in multiple input systems.
Digital Averaging Capabillty
Many spectral measurementscontain both discrete signals and random noise components.Obtaining proper amplitude readings can be
difficult if the random components are really the ones of interest or
are of nearly the same amplitude as the discrete signals.
The digital averaging techniques incorporated in the Model 3582A
help solve theseproblems. The RMS averaging mode takes the power
average of 4 to 256 successivespectra in order to reduce the uncertainty of the estimate of random spectral components.For measurements where the spectral information is not stahle hut varies slowly
with time, a running exponential form of RMS averalinl is provided.
By continually reducing the importance of older spectra. this mode
preventsold data from completely obscuring new data yet still retains
the basic advantales of averaginl.
When a synchronizing trigger signal is available, the TIME average can enhance the signal-to-noise ratio by as much as 24 da. Since
it involves the averaging of successivetime records before transformation it is also signjficantly fastet than other types of averaging.
Fully Annotated,
C811br8ted CRT DIspl8Y
One of the most important features of the Model 3582A is its ease
of use. Operator interaction with the instrument is simplified by the
combination of intelligent microcomputer control and the alphanumeric display capability. The basic annotation clearly shows the major measurement parameters.
Operational
Diagnostics
In addition to measurementresults, the display is used to provide
the operator with useful diagnostics. As the examples show, these
tend to not only indicate the problem, hut also to suggestan appropriate action.
Fig.
3A
Fig.
38
Figur.s 3A & 38: Operatlonal diagnostics not only show problem
but also suggest solution
SIGNAL ANAL YZERS
Dual-Channel,Real-TimeSpectrum Analyzer 0.02 Hz to 25.5 kHz
Model 3582A (cont.)
Service Dlagnostlcs
By pressing combinations of front panel keys, tbc instrument will
run self-diagnostic routines. Tbese include a lest of all tbc ROM,
RAM, front panel, display, recorder output and tbc digital filters.
The test results are displaycd on the CRT as eitber "OK" (correct) or
"ER" (error).
Powerful HP-IB Capabillty
The Hewlett-Packard Interface Bus (HP-IB) is an interface concept that allOWStwo-way communication among as many as fiftcen
different devices.Generally, at least one of tbese devices is a "computing controller" wbicb excrcises overall system control. Tbis controller directs and coordinates tbc activities of tbc otber devicesin tbc
system.
All major front panel controls witb tbc exception of tbc vemiers are
fully programmable via the HP-IB. Tbe programming codesare simple and are logically dcrived from tbc front panel controllabels. Tbe
states of tbc various controls occupy only ten 8-bit bytes of data tbat
can be read and written by tbc HP-IB. Tbis allows you to manually
set up a test from the front panel and store it in a compact form.
From the HP-IB it is a simple matter to command tbe Model
3S82A to output results in a usable fonn. Not only can tbc various
control settingsbe retrieved, but numcric marker data can be extractcd. More importantly, tbc full display can be read in ASCII fonnat
along with complete annotation.
The HP-IB structure is entirely flexible, allowing any of tbc RAM
(random accessmemory) in the instrument to be read or written into.
Tbis meanstbat intenncdiate computational results sucb as tbc cross
power spectrum can be read by a computing controller. In applica.
tions where speedis critical, tbc controller can transfer tbc displaycd
traces in binary, direct from tbc RAM. Tbe ability to write into tbc
RAM is also extremely valuable. For example, a perfect time record
can be synthesizedfrom a matbematical model and input to the instrument for analysis. More importantly, storcd display infonnation
such as the vibration signatures of a rotating machine can be input to
the instrument fot review. Also, the controller can matbematically
process
tbc storeddataandfonnat tbe resultsfot displayon tbc CRT.
Since the controller can also write its own CourliDesof alpbanumeric
tex~ tbe resultscan be properly annotatcd and calibratcd. Tbe operator can even be liven brief interpretation instructions-.l1 on the
CRT of the instrument.
ations of a prccision high frequency SOUTcc.
This is accomplishcd by
mixing the high frequency signal down to DC end measuring the
phase noise close-in to tbe carrier.
Fllte, Menurement
With dircct transfer function measurementsend tbe built-in driv.
ing source, the Model 3582A is weIl suitcd to pcrforming a network
analysisof low frequency devicessuch as filters. Figure 5 showsa five
scction low passelliptic filter.
Figur. 5:
Filter Tranafer Function
.
Te'ecommunIc8t1on8
Tbe frequency range and performance characteristics of the Model
3582A are weil matched to the R&.D and production needsof telecommunications. Voice frequency componentsincluding analog liDes
can be easily characterized.
Specialized signal sourcessuch as multifrequency tone sourcesand
modemscan poseunusual testing problems. Figure 6 shows the frequency spectrum of a modem transmitting astring of asterisks.
Figure 6:
Modem Spectrum
Audlo and Acoustics
Special Displays
Figure 4:
Are Poasible Under HP-IB Control
A Wide Range of Applicatlons
Includlng:
. Low frequency electronlc.
Ch8r8ct.rlz.
SIgnal Sourc..
Spectrum analyzers have typically been of major value in characterizing the harmonic distortion. spurious outputs, level and frcqucncy of signal sources. The model 3S82A not only makes these
measurcments bettet end more accurately tban before. but it also
makes them faster. Tbe additional combination of "real-time"
messurement speed and the powerful HP-IBcapability
make automated
testing of these parameters very attractive.
Ph.88 NolM Me..urement
In addition to characterizing
low frequency sources, tbe Model
3S82A can help characterize tbe short term random frequency fluctu-
T8pe Recorder Flutter
Tbe Model 3582A hai a number of features that make it weil suited
to the analysisof entertainment products. For example. an audio tape
recorder is a moderately complex electromechanical system.Any unwantcd mechanical speedvariations will show up as discrete modulation sidebandson a recordcd tone. With the frequency resolution of
the Model 3582A. it is possible to identify the sidebands preciselY
enough to relate them to actual geometries.
Loud.pe8kerT..tlng
Loudspeakersprovide another interesting application example. By
combining the built-in noise source with time averaging. it is possi~le
to obtain valid characterizations evenin tbe presenceof ambient nolse
as sbown in figure 7.
It is also possibleto use impulse type signals for this
.
Since tbe timerecord collection time is only a few milliseconds. tbiS
can minimize the echo problems.
With a slightly different hook-up the clcctrical impcdance of
loudspeakercan even be measurcd.
Figure 7:
Loud Speaker Response
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Structur.' .n.lyst.
A broad range of mechanical structures can be adequately described as linear systemsand can be characterized by their frequency
domain transfer functions. These transfer functions relate applied
forces and the resulting motion. This example illustrates the driving
~int inertance (acceleration/force) transfer function of a small
beIm.
DC response: Adjustableto >40 dB belowmaximuminput level
Accuracy:
Accuracy at the
:t:0..1dB
PassbandCenter
Flat top filter:
+0, -0.1 dB
Hannlng filter:
+0, -l.S dB
Uniform filter:
+0, -4.0 dB
Note: Overallaccuracyis the sumof the accuracyat the pusband
centerplusthe selectedfilter accuracy.
Resolution:
Log: 0.1 dB
Unear: 3 digits
Phase
Display range: +200 degreesto -200 degrees
Accuracy: :t 10degrees
Resolution: 1 degree
Transfer Functlon
Measurementrang.:
Log: + 160dB full scaleto -80 dB fu" scale
Linear: 4 X 10' fu" scaleto 4 X lo-a fu" scale
Phasedisplay range: + 200degreesto - 200degrees
Accuracy:
Amplitude: :t0.8 dB
Pha..: j: 5 degrees
Accuracy: Option 001
Amplitude
.
I
I
.02 HZ
0:448
:2:2-
r
I
0...
:2:5-
.1kHz
I
I
25..1kHz
Coherence
Measurement rang.: 0.0 bottom display liDe to 1.0 top display liDe
Resolution: 0.01
Input
ImpedanC8: 10' n :t.5% shuntcd by <60 pF rrom input high to low
(ror less than 75% relative humidity)
Isolation: Input low may be floatcd up to 30V
Coupllng: Switch selectionof AC or DC couplins. The low rrequency
Figure 8:
Driving Point Inertance
. RotaUng machlnery Ifgnature.
Every rotating machine exhibits a unique characteristic vibration
pattern determincd not only by tbc basic design and construction of
tbc machine. but also by environmental factors and Weaf. With tbc
appropriate transduccrs the Model 3S82A can mcasurc and analyze
these vibration patterns or "signatures."
3582A Speclflcationa
Frequency
Range:0.02Hz to 25.5kHz with tbelowfrequencylimit tberesultof
DC response.
Span.: 1 Hz to 25 kHz in a 1-2.5-5-10 sequence.The 1 Hz and 2.5
Hz spansare usable only in the O-start mode.
Accuracy: :t 0.003% of display center frequency.
R..olutJon: 0.4% of tbe frequency span for single channel or 0.8% of
the frequency span for dual channels.
Filter pa..band .hape:
Flat Top
Hannlng
Uniform
3 dB Bandwldth (1.4 :t0.1% (0.58 1:0.05% (0.35 :t0.02%
(single chann.l)
of span)
of span)
of span)
Shap. Factor
2.6 :t0.1
9.1 1:0.2
716 ::t20
Amplitude
Display mode.:
Log: 10 dB/division or 2 dB/division
LInear: Constant voltage/division
Mea.uremen' range:
Log: +30 dBV to -120 dBV noise noor
LInear: +30 V to I"V noise noor
Dynamlc ranoe: 70 dB
3 dB roll off is < 1 Hz.
Commonmode re)ectlon:
50 Hz: >60 dB
60 Hz: >58 dB
Crosstalk: <-140 dB betweenchannelswith 1 kn SOUrte
impeciancedriving ODechanDeiand the other terminatedin 1 kn.
Output
X-Y recorder:
Level: OVto 5.25V :t:5%
Impedance: 1 k!2
Pen Hft: contactclOlureduring sweep
Nol.. source:
Type: Periodicpseudorandum
noiJeor randomnoiJesignalwith
switch selection.80th are band limited and band translatedto
matchthe analysis.
L.vel: From <10 mV to >500 mV RMS into >50 n
Imp.danc.: <2 n
General
Envlronmental:
Temperatur.: O°Cto 5SoCoperating;-40°C to +7SoCItonp
Humldlty: <95% R.H. O°Cto 40°C
Power r.qulr.ment8: 100.120.220.or 240voltl (+S"'. -1~); 4866 Hz; lessthan lS0 VA
Dlm.nslons
5lze: 42S.S W x SS2.S D x 188 mmH (16.7S' x 21.7S' x 7.4')
Welght: 24.S kg (S4 Ibs.); shippping weight: 29 kl (63 IbI.)
Options
Opt 001: High AccuracyTransferFunction
Measurement
Option
3582A Spectrum Analyzer