Reducing Uncertainty in

EMC Measurements

Uncertainty

“In general, a standardized EMC test must be

developed such that reproducible results are

obtained if different parties perform the same test

with the same EUT.

However, various uncertainty sources and

influence quantities cause the reproducibility of a

standardized EMC test to be limited.”

(From CISPR 16-4-2 introduction)

Status of Cispr 14-4-2

First published in 2002 a Cispr 16-4.

Then split up in Cispr 16-4-2:2003 (same as Cispr 16-4).

Applied by product standards: Cispr 11 (Amd 2:2006-06

and Cispr 22:2005 (5th ed.).

Only a statement of ULab in the report needed.

New proposal to check if ULab exceeds UCispr.

Publication is due in 2010

CISPR16 Uncertainty

CISPR recommendations and technical reports

•CISPR 16-4-1 Uncertainty in standardized EMC Tests •CISPR 16-4-3 Statistical consideration in the determination of EMC

compliance of mass Product

•CISPR 16-4-4 Statistics of complaints and model for the calculation

of limits

•CISPR 16-4-5 Uncertainties, statistics and limits modelling –

Conditions for use of the alternative test methods

CISPR Editions on uncertainties in EMC measurements

•CISPR 16-4-2 Measurement instrumentation uncertainty

Focusing on Emission Testing

Measurement Instrumentation Uncertainty MUST be

taken into account when determining compliance or

non-compliance with a disturbance limit.

The Measurement Instrumentation Uncertainty for a

Test Laboratory (Ulab) MUST be evaluated for the

measurements addressed in CISPR 16-4-2 clauses,

taking into account every single quantity listed there.

Focusing on Emission Testing

CISPR 16-4-2 Standard clearly defines

Uncertainty topics for Emission Tests, whose

most relevant contributions come from:

- EMI/EMC Receivers

- Test Set-Up (layout, cables, adapters, site attenuation,…)

- LISNs and AMNs in general (ISNs, CDNs, Voltage

Probes,…)

- Absorbing Clamps

- Antennas

- Coupling between above components

Uncertainty Evaluation Formula

Combined Standard Uncertainty

where

xi = estimate of input quantity Xi

u(xi) = standard uncertainty of xi

ci = sensitivity coefficient

y = result of a measurement (the estimate of the measurand),

corrected for all recognized significant systematic effects

(i.e. estimate value of xi)

CISPR 16-4-2 example

UCISPR Reference Table

Compliance Assessment by CISPR 16-4-2

The Expanded Measurement Instrumentation Uncertainty

Ulab for a test laboratory shall be calculated using:

A graphical example

Receiver Uncertainty Contribution

• In Radiated & Conducted Emission measurements

the receiver is the most complex equipment due to:

– Sophisticated measuring functions

– Large number of active & passive components

– Effect of aging on calibration

– Effect of environmental factors on calibration

Item

(Receiver Specification)

CISPR

Specified

Uncertainty

(dB)

Digital

Receiver

Uncertainty

(dB)

Receiver Reading ± 0,1 ± 0,1

Receiver Correction:

Sine wave voltage

Pulse absolute calibration

Pulse repetition rate @1Hz

± 1,0

± 1,5

± 2

± 0,15

± 0,2

± 0,2

Analog to Digital Receivers

Uncertainty Budget Comparison

PMM 9010 10 Hz - 30 MHz

Item

(Receiver Specification)

CISPR

Specified

Uncertainty

(dB)

Digital

Receiver

Uncertainty

(dB)

Receiver Reading ± 0,1 ± 0,1

Receiver Correction:

Sine wave voltage

Pulse absolute calibration

Pulse repetition rate @ 20 Hz

Pulse repetition rate @ 1Hz

± 1,0

± 1,5

± 1

± 2

± 0,3

± 0,5

± 0,2

± 1,3

PMM 9030 30 MHz – 3 GHz

Analog to Digital Receivers

Uncertainty Budget Comparison

9030/9060 direct antenna matching via Fiber Optic

Digital signal from ADC

An innovative way to reduce uncertainty: bringing the receiver to the antenna!

A simple test: coax cable vs. f/o

1) Simulation of an antenna connected to the receiver by coaxial cable

10 + 10 m

Coax cable RG213U

N – N transition

3 GHz EMI Receiver PMM 9010 + 9030 full CISPR 16-1-1 compliance

Fiber Optic

Digital Link

Chamber

2) Simulation of:

direct connection antenna – receiver remote unit

receiver main unit connected by fiber optic

A simple test: coax cable vs. f/o

3 GHz EMI Receiver PMM 9010 + 9030 full CISPR 16-1-1 compliance

Fiber Optic

Digital Link

Chamber

A simple test: coax cable vs. f/o

1) Simulation of an antenna connected to the receiver by coaxial cable

Gen Pulsed 1 Hz -> Cable -> RX

30

35

40

45

50

55

60

30 200 600 1000 1400 1800 2200 2600 3000

dB

uV

PK

QP

C-AVG

A simple test: coax cable vs. f/o

2) Simulation of:

direct connection antenna – receiver remote unit

receiver main unit connected by fiber optic

Gen Pulsed -> RX

35

40

45

50

55

60

65

30 200 600 1000 1400 1800 2200 2600 3000

dB

uV PK

QP

C-AVG

A simple test: coax cable vs. f/o

Loss of dynamic range

0

5

10

15

20

30 200 600 1000 1400 1800 2200 2600 3000

dB

PK

QP

C-AVG

Additional loss: antenna factors

Coax cable reduces sensitivity.

Lower sensitivity could lead to incorrect weighting

Thus, usually a preamplifier close to antenna is used

BUT

Account for mismatch uncertainty twice

First: Antenna/Preamp

Second: Preamp/Receiver

Gen Pulsed 1 Hz -> Cable -> RX

30

35

40

45

50

55

60

30 200 600 1000 1400 1800 2200 2600 3000

dB

uV

PK

QP

C-AVG

ANALOGUE TO DIGITAL UNCERTAINTY COMPARISON

Input Quantity

Analogue uncertainty contribution

(typical) in dB

PMM 9010 uncertainty

contribution

Receiver reading ±0,1 Equal or better

Aging TBD, but present Absent

Attenuation: Antenna-receiver Cables Connections

±0,1

TBD, but present TBD, but present

Equal

Absent Absent

Receiver correction: Sine wave voltage Pulse amplitude response Pulse repetition rate response

±1,0 ±1,5 ±1,5

Better Better Better

Mismatch: antenna-receiver antenna-cable cable-cable

+0,9/-1,0

TBD, but present TBD, but present

Equal Absent Absent

Cable-Antenna (or other transducer, e.g. E.M. clamp) balance

±0,9

Better (w/ 9030-9060)

Cables coupling to ground

TBD, but present

Absent with 9030 or 9060

Other benefits from Split Architecture

No expensive coaxial cables

No cable loss

No cable/antenna coupling

No cable scattering

No connectors loss

Antenna decoupling not needed

Higher flexibility of Optical cable

Longer connection distance (100 m)