EMC seminar Page 1 Misure di pre-compliance EMI Roberto Sacchi Application Engineer [email protected]
EMC seminar
Agenda
Introduzione alle misure EMI Terminologia;
Sistema di misura (antenna, LISN, ricevitore, etc.);
Detectors;
Normative europee ed internazionali
Misure di pre-compatibilita’ elettromagnetica Misure di emissioni radiate;
Misure di emissioni condotte
Soluzioni Agilent Introduzione agli analizzatori serie-X;
Software applicativo per le misure di pre-compatibilita’ EMI
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Comparison of precompliance and full compliance
measurements
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Precompliance MeasurementsEvaluate the conducted and radiated
emissions of a device using correct
detectors and bandwidths before going
to a test house for compliance testing
Full Compliance measurements
Full compliance testing requires a receiver
that meets all the requirements of CISPR
16-1-1 (response to a CISPR pulse gen),
a qualified open area test site or semi
anechoic chamber and an antenna tower
and turntable to maximize EUT signals.
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What is EMC?
Electromagnetic Compatibility (EMC): The ability of equipment to function
satisfactorily in its electromagnetic environment without introducing intolerable
disturbances into that environment or into other equipment.
Combination of Interference and Immunity.
Electromagnetic Interference (EMI):Electromagnetic energy emanating from one device which causes another device to
have degraded performance.
Electromagnetic Immunity (Susceptibility, EMS): Tolerance in the presence
of electromagnetic energy (Performance degradation due to electromagnetic energy).
Compliance measurements require a receiver that meets the requirements of
CISPR part 16 (for commercial) or MIL-STDd 461 (for military).
All EMI receivers require a pre-selector at lower frequencies to limit the input energy
and maintain sufficient dynamic range to meet the CISPR 16 requirements.
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Definitions
EMC –
ElectroMagnetic Compatibility
EMI –
ElectroMagnetic
Interference
EMS –
ElectroMagnetic
Susceptibility
(aka Immunity)
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OverviewWhat is Signal, Vector and Spectrum Analysis?
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•Display and measure amplitude versus frequency for RF & MW signals
•Separate or demodulate complex signals into their base components (sine waves)
Spectrum Analysis
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OverviewTypes of Tests Made
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Modulation
Noise
Distortion
EMC
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Architecture of Modern Spectrum/Signal Analyzers
What does “Modern” mean?
Digitize the IF output, not detector output
FFT and swept capability (neither one is optimum for everything)
Digitized data output available
Connectivity
Automated measurement features
What we hope it doesn’t mean
Incompatibility
What can it mean
Ability to use new features to duplicate or expand necessary old ones
Complete spectrum analyzer & vector signal analyzer
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Theory of OperationSwept Spectrum Analyzer Block Diagram
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Pre-Selector
Or Low Pass
Input Filter
Crystal
Reference
Oscillator
Log
Amp
RF input
attenuator
mixer
IF filter
(RBW)envelope
detector
video
filterlocal
oscillator
sweep
generator
IF gain
Input
signal
ADC, Display
& Video
Processing
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Traditional Spectrum Analyzer
Scalar analysis
Digitizing the video signal
Classic superheterodyne swept spectrum analyzer
Product detector
loss of phase
information
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Digital IF Spectrum/Signal Analyzer
Vector data CAN be preserved (mag/phase or I/Q)
Digitizing the IF Signal
Some troublesome operations
and conversions are now
fast, accurate DSP
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OverviewDifferent Types of Analyzers
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Parallel filters measured
simultaneouslyA
ff1 f2
FFT Analyzer
A
ff1 f2
Filter 'sweeps' over
range of interest
Swept Analyzer
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SpecificationsResolution: RBW Type Determines Sweep Time
280 sec
134 sec
13.5 sec
8563E Analog RBW
PSA Digital RBW
PSA FFT RBW
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Speed Improvements
Useful comparisons highly specific, many factors
PXA mode switching typically faster than PSA
Where speed is critical, consider modifying measurement routines to
include features such as list sweep
Benchmark PXA PSASpeed
improvement
Preset (*RST) 28 ms 168 ms 6x
Marker peak search 6.5 ms 78 ms 12x
Local Update 13 ms 17 ms 1.3x
CF Tune and Transfer (4 - 5GHz) 109 ms 186 ms 1.7x
Remote sweep and trace transfer 18 ms 30 ms 1.67x
Nominal speed comparison, PSA example:
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Modern spectrum analyzer
Resolution BW Selectivity or Shape Factor
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3 dB
60 dB
60 dBBW
60 dB BW
3 dB BW
3 dB BW
Selectivity =
Determines resolvability of unequal amplitude signals
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Specifications
Resolution: RBW Type and Selectivity
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DIGITAL FILTER
ANALOG FILTER
SPAN 3 kHzRES BW 100 Hz
Typical
Selectivity
Analog 15:1
Digital ≤5:1
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Digital Filter Shape
Better shape factor, biggest selectivity benefit for different signal levels
Equivalent selectivity at a wider, faster-sweeping RBW
digital filters swept an additional 3-4x faster
30 kHz Digital Filter
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CISPR Bandwidth Requirements
Measurement Range CISPR Band CISPR Bandwidth
9 KHz – 150KHz A 200 Hz
150 KHz – 30 MHz B 9 KHz
30 MHz – 1 GHz C/D 120 KHz
> 1GHz E 1 MHz
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Bandwidth -6dB
-20dB
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MIL-STD-461 Bandwidth Requirements
Measurement Range -6dB Bandwidth
30Hz - 1 KHz 10 Hz
1 KHz -10 KHz 100 Hz
10 KHz - 150 KHz 1 KHz
150 KHz - 30MHz 10 KHz
30 MHz - GHz 100 KHz
> 1GHz 1 MHz
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Some modern analyzers approach accuracy of power meter + sensor
• Even better for low-level signals, with narrower noise bandwidth and
the benefit of frequency selectivity
Some factors determining uncertainty:
• Input connector (mismatch)
• RF input attenuator
• Mixer and input filter (flatness)
• IF gain/attenuation (reference level)
• RBW filters
• Display scale fidelity
• Calibrator
Modern Spectrum Analyzer Accuracy
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Modern Spectrum Analyzer Accuracy Examples
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Line Impedance Stabilization Networks (LISN)
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Purpose of a LISN:
1. Isolates the power mains from the
equipment under test. The power
supplied to the EUT must be as clean as
possible. Any noise on the line will be
coupled to the X-Series signal analyzer
and interpreted as noise generated by
the EUT.
2. Isolates any noise generated by the EUT
from being coupled to the power mains.
Excess noise on the power mains can
cause interference with the proper
operation of other devices on the line.
3. The signals generated by the EUT are
coupled to the X-Series analyzer using a
high-pass filter, which is part of the LISN.
Signals that are in the pass band of the
high-pass filter see a 50-Ω load.
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LISN
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LISN
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@ Electrical Network Frequency
@ 150 kHz to 30 MHz
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Transient Limiter
The purpose of the limiter is to protect the input of the EMC analyzer from
large transients when connected to a LISN. Switching EUT power on or off
can cause large spikes generated in the LISN.
The Agilent 11947A transient limiter incorporates a limiter, high-pass filter,
and an attenuator. It can withstand 10 kW for 10 μsec and has a frequency
range of 9 kHz to 200 MHz. The high-pass filter reduces the line frequencies
coupled to the EMC analyzer.
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DUT
LimiterLISN
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Field Strength and Antenna factors
Radiated EMI emissions tests measure the electric field. The
field strength is calibrated in dBμV/m.
Antenna factors is the ratio of the electric field (V/m) present
at the plane of the antenna versus the voltage out of the
antenna connector.
Log units:
AF(dB/m) = E(dBμV/m) - V(dBμV)
E(dBμV/m) = V(dBμV) + AF(dB/m)
Notes:
Antenna factors are not the same as antenna gain.
dBμV = dBm + 107
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Field Strength Unit
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Radiated EMI emissions measurements measure the
electric field. The field strength is calibrated in dBμV/m.
Pt = total power radiated from an isotropic radiator
Pd = the power density at a distance from the isotropic radiator
(far field >λ/2π)
24 r
PP t
d
120R
R
EPd
2
2
2
4 r
P
R
E t
r
PE
t 30 [V/m]
[ohm]
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Antennas used in EMI emission measurements
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Detectors: Convert IF Samples to Display Bins or
“Buckets”
Multiple simultaneous detectors
Screen Shot “Detector 3types”
Time
Volts
Peak
Neg Peak
Sample
Display points or
buckets
Normal, Average, Neg Peak
Peak, Neg Peak, Sample
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Detectors
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Most radiated and conducted limits are based on quasi-peak
detection mode.
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Peak vs. Quasi-peak vs. Average
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time
VPeak Detection
Quasi-Peak Detection
Average Detection
time
VPeak Detection
Quasi-Peak DetectionAverage Detection
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Peak ≧ QP ≧AveragePeak Detector
• Initially used
• Faster than QP and Average modes
• If all signals fall below the limit, then the product passes and no future
testing is needed.
QP
• For CW signal, Peak = QP
• Much slower by 2 or 3 order magnitude compared to using Peak detector
• Charge rate much faster than discharge rate
– the higher repetition rate of the signal, the higher QP reading
Average
• Radiated emissions measurements above 1 GHz are performed using
average detection
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Close field probe
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Measures the magnetic field H strength at the center
of its sense loop. The plane of the probe tip loops
must be perpendicular to the radiating magnetic field
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Test example
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Emissions Regulations (Summary)
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European Norms example
EN55014 (CISPR 14)
This standard applies to electric motor-operated and thermal
appliances for household and similar purposes, electric tools
and electric apparatus.
Limit line use depends upon the power rating of the item.
EN55014 distinguishes between household appliances, motors
less than 700W, less than 1000W and greater than 1000W.
Limits for conducted emissions are 150 kHz to 30 MHz, and
limits for radiated emissions are 30 MHz to 300 MHz.
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The pre-compliance measurement process
Before making measurements on your product, some
preliminary questions must be answered.
1. Where will the product be sold (for example, Europe, United
States, Japan)?
2. What is the classification of the product?a. Information technology equipment (ITE)
b. Industrial, scientific or medical equipment (ISM)
c. Automotive or communication
d. Generic (equipment not found in other standards)
3. Where will the product be used (for example home,
commercial, light industry or heavy industry)?
With the answers to these questions, you can determine
which standard your product must be tested against.
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General Process for Making EMI Measurements
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Determine the country or countries in which the product
will be sold which in turn identifies the regulator agency.
Select the limit lines to be tested to (conducted/radiated).
Select the band to be used.
Correct for transducer loses and amplifiers gains.
Identify signals above the limit that must be evaluated.
Zoom in on failed signal and perform quasi-peak or
average measurements.
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Conducted Emissions Measurements
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1. Connect DUT to the test system
2. Set the proper frequency range
3. Load limit lines and correction factors for LISN and limiter
4. View the ambient emissions with DUT OFF
5. Switch on the DUT and find signals above limits by using peak detector
6. Measure all signals above limits with quasi-peak and average detectors
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Radiated Emissions are difficult to
measure because of multiple
dimensions (five) and the use of
quasi-peak detection below 1GHz
41.2563MHz
218.120MHz
1500.260MHz
1 - Azimuth
2 - Antenna Height
3 - Field Strength
4 - Frequency
5 -Time
The challenge of measuring radiated emissions
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Radiated Emissions Measurements
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1. Connect the antenna to the EMI receiver and separate the antenna from
the DUT as specified by the regulation requirements
2. Set the proper frequency range and bandwidth
3. Load limit lines and correction factors for antenna and cable.
4. With DUT OFF, measure the ambient emissions and store them
5. Switch on the DUT and find signals above limits by using peak detector
(only those not present during the ambient scan)
6. Measure all signals above limits with quasi-peak and average detectors
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1. Select the measurement range
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2. Load Corrections factors
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Amplitude at
point circled
Amplitude
referenced to
blue line
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3. Load Limit line
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Circle indicates
the position of
the amplitude
frequency pair
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4. Scan for signals above the limits with peak
detector
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5. Quasi-peak and average measurements
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Troubleshooting
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Use the close-field probe to locate the sources of the radiated signals
exceeding the limit lines
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Agilent Solutions
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Agilent X-Series Signal Analyzers
Multiple instruments in one box: Swept spectrum analyzer;
FFT analyzer;
RF and Baseband Vector Signal analyzer;
Noise Figure analyzer.
Fastest signal analysis measurements
Broadest set of applications and demodulation capabilities
Upgradeable HW
Most advanced user interface & world-class connectivity
Instrument ArchitectureModern Spectrum Analyzers Architecture (PSA, X-Series)
RF Section IF Section BB Section
•Attenuation
•Filtering
•Downconversion• RBW Filtering
• Envelope Detection
• Log Conversion
• VBW Filtering
• Peak/sample/rms
detection
• Averaging
ADCIF/BB Section
on ASIC
“All Digital” IF Architecture
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Modern Spectrum Analyzer Block Diagram
YIG ADC
Analog IF
FilterDigital IF Filter
Digital Log Amp
Digital Detectors
FFT
Swept vs. FFTAttenuation
Pre-amp
Replaced
by
“All Digital IF” Advantages
RF Section ADCIF/BB Section
on ASIC
Flexibility:
RBW filtering in 10% steps
Filters with better selectivity
Multiple operation modes (Swept, FFT, VSA, NFA)
Accuracy:
Log conversion practically ideal
No drift errors; increased repeatability
Speed:
When Swept mode is slow, go FFT
FFT
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Techniques for Reducing DANL, Improving Dynamic
Range
Reduce attenuation
Add preamp
Reduce RBW
Add external filtering
Better/shorter cables, connectors
Move analyzer closer
Time averaging (where possible, not measurement avg.)
Measurement processing (take advantage of Moore’s Law)
• Noise power subtraction/noise correction/NNC
• Noise floor extension (NFE) leverages deep knowledge of
analyzer/circuit behavior
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CW Signal Measured Near Analyzer Noise Floor
Actual S/N
Displayed
S/N
CW Signal
Apparent
Signal
This is
fundamental, and
often missedAmpl & Freq
Axes Expanded
Example: No noise subtraction or near noise correction
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Noise Subtraction, “Noise Floor Extension”
New PXA technique “NFE” improves D.A.N.L.
analyzer noise power calculated/subtracted real time
3 dB error
without NFE
“No” error
Improved noise floor
or displayed average
noise level
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Noise-Like Signal and Noise
1 MSymbol/sec QPSK, 1.9 GHz
Signal accurately measured, but noise biased higher by analyzer
noise power (no NFE)
Average detector, slower sweep to measure signal and noise,
reduce variance
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Result from Noise Subtraction
Implemented in the Agilent PXA Signal Analyzer
Blue trace shows more accurate measurement due to removal of analyzer noise power
Note increased variance of result
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Analyzer Noise Floor without NFE
Source switched off, pink trace shows analyzer noise level, no NFE
Other measurement conditions unchanged
PXA DANL (pink) adds to source power (blue) for first meas. result (yellow)
Note that noise level variance (pink trace) is smaller without NFE
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Analyzer Noise Floor with NFE
Source still off, green trace shows analyzer noise level with NFE
Other measurement conditions unchanged
Note high variance result from subtraction of small, noisy numbers
Analyzer DANL now far enough below source for minimal(0.2 - 0.4 dB) error
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A Closer Look
Pink trace adds to blue trace; result is yellow trace (NFE not used)
Green trace is included in blue trace but resulting error very small
Source noise Level, no NFE
Source Noise Level, with NFE
Analyzer Noise, no NFE
Analyzer Noise with NFE
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Signal Type vs. EffectivenessSignal/Noise Variation with RBW
Amplitude envelope vs. time
Best RBW is one matched to signal
Best ability to separate analyzer noise from signal
RBW (log)
SNR
(dB)
Noise-like
Real signals
can be one
type or
combination
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Noise Floor EnhancementCW Example
95% confidence interval, 2 dB tolerance
3.5 dB improvement for CW signal
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Noise Floor EnhancementNoise-Like Signal Example
95% confidence interval, 1 dB tolerance
9.1 dB improvement for noise-like signal
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Noise Floor EnhancementPulsed RF Example
95% confidence interval, 3 dB tolerance
10.8 dB improvement for pulsed-RF signal
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Low Noise Path
To μW
Converters
To Low Band
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Alternate “Low Noise Path”
3 dB
@ 3.6 GHz
10 dB
@ 26 GHz
Example:
Spur Search
20-50x faster
at 18 GHz
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Combining Noise Floor Extension and Low Noise Path
3.6 - 26.5 GHz, preamplifier off
Low noise path incompatible with preamp, >3.6 GHz only
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Noise Figure Measurements with a Spectrum/Signal
Analyzer and NFE
Noise Figure Measurement Application
Perf. Comparable to Dedicated Noise Figure Analyzer
NFE Offers an Additional Calibration Type
Faster/easier but less precise
NF
un
ce
rta
inty
(d
B)
NF Uncertainty vs. Cal Type
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Noise Floor Subtraction
Analyzer noise adds incoherently to any signal to be measured
Power calculations are performed on a linear power scale
(watts, not dBm) and results typically are shown in dBm
PobsS+N = PobsN + PS
PS = PobsS+N − PobsN
EMI Roadmap
10/25/2010Page 72
EMC Features standard in X-Series:(today)
• Limit Lines (2000 pts)
• Amplitude correction (2000 pts)
• 40001 sweep points
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Option EMC in X-Series:(available today)
CISPR 16-1-1 detectors
(to latest spec)
Quasi Peak
EMI Average (“CISPR-AVG”)
RMS Average (“CISPR-RMS”)
EMI Bandwidths (CISPR & MIL STD)
EMI Presets
Tune & Listen
Measure at Marker
EMI Peak, EMI Average, and
Quasi Peak measurements
displayed together
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Full Featured Pre-compliance Application
Ship Nov 2010
Available in all X-Series models
W/N6141A EMC measurement application
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Corrections factors edit display
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Amplitude at
point circled
Amplitude
referenced to
blue line
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Limit line edit display
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Circle indicates
the position of
the amplitude
frequency pair
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Log Display
Peak List
Auto-detect peaks
Limit Delta
Realtime
Meters
with any 3
Simultaneous
Detectors
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N6141A measurement: Frequency Scan with Log Display
- same functionality as E7400 Signal List
Meters tune
to selected
signal
EMI Roadmap
10/25/2010Page 79
N6141A measurement: Strip Chart
• Time record
of zero span
data scrolls
to left
• Up to three
different
detectors
• Can be used
to make
“click”
measure-
ments
Click measurements are made on home appliances
Patent
Applied
For
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Option EDP (Enhanced Display Package)
for the SA- available November 2010 • Spectrogram
• Trace Zoom
• Zone Span
Group/Presentation Title
Agilent Restricted
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Summary
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Pre-compliance
solutions
PXA, MXA, EXA,CXA
N6141A EMC advanced
measurement application
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Per documentazione su prodotti ed applicazioni EMI/EMC visitare il sito
http://www.agilent.com/find/EMC
Contatti:
Agilent Technologies ItaliaGiuseppe SavoiaSignal Analysis and Generation SpecialistE-mail: [email protected]
Agilent Contact CenterE-mail: [email protected]: 02 9260 8484
EMC seminar
Setup instructions for the N6141A EMC
measurement application
Press [Mode], more, {EMI Receiver}
Press [Meas], {Frequency Scan}
Press [Meas Setup], {Scan Table}, {Range 3 on}, {Range 5 off}
[Return] {Signal list}, {Delete Signals}, {Delete all} OK
Press [Mode Setup], {meter control},{meters}, {Select meter 1},
{Meter on}, {Select meter 2}, {Meter on}
Press [Meas Setup], {Scan Sequence}, {Scan only}, more
{Search criteria}, {Peak criteria and limits}, {Limits}, {Limits
on}, {Margin -6 dB}