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EMC and Audio Equipment -. EN55103-1 and EN55103-2. Mark Briggs, Elliott Labs ([email protected]). Outline of the presentation. The CE Mark The EMC Directive Professional Audio Equipment EN55103-1 - Emissions Standard EN55103-2 Immunity Standard Designing to meet the standards.

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EMC and Audio Equipment -

EN55103-1 and EN55103-2

Mark Briggs, Elliott Labs ([email protected])


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Outline of the presentation

The CE Mark

The EMC Directive

Professional Audio Equipment

EN55103-1 - Emissions Standard

EN55103-2 Immunity Standard

Designing to meet the standards


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The CE Mark

  • Required to sell products into Europe.

  • Used to declare compliance to applicable Directives. (link to directives)


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The EMC Directive

  • EMC = Electromagnetic Compatibility.

  • Two essential requirements:

    • The product does not interfere with bona fide users of the radio spectrum (Emissions)

    • The product will operate when subjected to interference from bona fide users of the radio spectrum and to naturally occurring EM phenomena (Immunity)


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Demonstrating Compliance

  • Declare compliance to the most applicable standard

    • Standards are listed in the Official Journal of the European Union

  • If a standard does not exist or cannot be applied, use a Technical Construction File (TCF)

    • A “Competent Body” reviews the manufacturers technical file which provides justification to why the product meets the essential requirements. Typically the Competent Body will base their interpretation of “essential requirements” on the most applicable standard


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Standards Route

  • Manufacturer declares compliance by stating that the product meets the requirements of the most applicable standard(s) for emissions and immunity

  • Nowhere does it state that you must test - the actual wording is that you “... apply the standard(s)”

  • Standards are listed in the Official Journal (OJ) of the European Union(link)

  • Product specific standards take precedence. There are generic standards for products which do not have a specific standard


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What about new standards ?

  • As standards get revised or as new product standards are released, the OJ will list the “Date of cessation” for the superseded standard

  • Products sold after the cessation date must meet the requirements of the new standard

  • In the transition period either the new or old standard may be used.


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Technical Construction File

  • Manufacturer prepares a technical file which provides justification as to why the product meets the essential requirements.

  • The file contains

    • product descriptions,

    • design details (with emphasis on EMC design techniques)

    • Results from any EMC tests performed

    • Description of intended operating environment and the EMC phenomena present in that environment

  • A Competent Body reviews the file and, if it considers the essential requirements are met, issues a technical certificate.


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Demonstrating Compliance

  • A declaration of Conformity (DoC) is produced which details the product name, manufacturer, Directive(s) and standard(s) or Technical certificates.

  • It is a “good idea” to keep a technical file when using the standards route. This would provide the evidence to a European court if complaints were ever made against a manufacturer.

  • Apply the CE Mark to the product

  • Maintain a copy of the DoC with the European distributor for ten years after the last product is sold.


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Professional Audio Equipment Standards

  • EN55103-1 (Emissions)

  • EN55103-2 (Immunity)

  • Effective as of September 1st 1999

  • The scope of the standards covers professional audio, video, audio-visual and entertainment lighting control equipment.


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Definitions

  • Professional: Apparatus for use in trades, professions or industries that is not intended for sale to the general public.

  • Audio, video, audio-visual and entertainment lighting control equipment:

    • Designed for the purposes of controlling audio, video, audiovisual or entertainment lighting characteristics;

    • Designed for processing audio, video or lighting control signals in digital form;

    • Designed to control the intensity, color, nature or direction of light from luminaries with the intention of creating artistic effects in theatrical, televisual or musical productions and visual presentations.


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Products NOT covered by EN55103

  • Consumer apparatus (Sound cards)

    • These would probably fall under EN55022/EN55024 for PC-based cards. EN55013/EN55020 apply to Broadcast receivers and associated equipment (stereo components)

  • Apparatus specifically designed for security systems (CCTV video equipment)

    • These would fall under the standard for alarm systems

  • Radio communications devices (wireless microphones)

    • Radio communications equipment have their own specific standards


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Requirements

  • The limits on the emissions from products are defined in EN55103-1

  • The immunity requirements are detailed in EN55103-2

  • Limits and test levels depend on the intended environment of the product


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Product Environments

  • E1: Residential environment

  • E2: Commercial and light industrial (e.g. theatres)

  • E3: Urban outdoors

  • E4: controlled EMC environment (e.g. purpose built broadcasting/recording studios, rural outdoors some distance from railways, transmitters, overhead power lines etc.). It should be noted that some studios might be considered as environment E2.

  • E5: Heavy industrial environment and environments close to broadcast transmitters.


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EN55103-1 Emissions


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Emissions Tests


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Radiated Emissions, 30 - 1000 MHz

  • Should be tested on an Open Area Test Site (OATS) or a suitable emissions chamber

  • For FCC testing, the frequency range may extend above 1GHz (1000MHz) :

    • If the highest frequency generated/used is > 108MHz then test to 2 GHz

    • If the highest frequency > 500 MHz then test to 5 GHz

    • If >1 GHz then test to 5x frequency


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Radiated Emissions, 30 - 1000 MHz

  • Emissions tend to occur at harmonics of the digital clocks plus power-supply switching harmonics !

  • Emissions require an antenna with a length greater than /10 (30m / f in MHz)

  • Generally the emissions below 300 MHz are due to common mode noise on external interface cables

  • Above 300 MHz emissions tend to radiate from slots in the enclosure

  • Best controlled through good circuit layout


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Radiated Emissions, 50Hz - 50kHz

  • Tested using a loop antenna as specified in the EN55103-1 standard

  • Loop can be made (or purchased - it is equivalent to mil Std 461 RE101 Loop antenna)

  • For rack-mount equipment, test at 10cm. For other, test at 1m

  • Typically problem frequencies will be

    • Switching frequency of power supply

    • Harmonics of AC frequency due to diode switching action


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AC Conducted Emissions

  • Limits the rf voltage between line/neutral and ground in the frequency range 0.15 - 30 MHz

  • Use a LISN to measure the voltage (cost about $3000) with an EMI receiver ($30,000) - however a pre-compliance analyzer may be purchased for about $15,000 (Agilent EM-series)


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Signal and I/O Conducted Emissions

  • Limits the common mode current /voltage on signal lines and dc power in the frequency range 150kHz - 30 MHz

  • For shielded lines, the test is performed with the shield terminated to ground via a 150 ohm resistor

  • Unshielded cables - common mode termination by tying each signal lead to ground via a 150 ohms x n resistor (n = number of signal lines)

  • RF current probe is placed around the signal lead to be tested


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Signal and I/O Conducted Emissions

Termination of a shielded cable


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Signal and I/O Conducted Emissions

Termination of a four-wire, unshielded cable


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AC Current Harmonics

  • This test restricts the current harmonics that can be produced by a power supply.

  • If using an external PS vendor, specify that it must meet the EN61000-3-2 standard

  • Typically a power-factor-corrected (pfc) supply will meet the requirements on harmonic current emissions

  • Could use vendor data to show compliance with requirements (make sure they tested at power rating of your product)


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AC Voltage Flicker

  • “Flicker” is the effect caused when a large load current is switched, creating a short-duration dip in the AC voltage (e.g. refrigerator, when compressor switches on the lights dim momentarily)

  • Can only be measured with a custom-built test equipment - but could be evaluated using a light bulb connected to the same AC outlet ?


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Other Emissions Tests

  • Discontinuous interference

    • Click interference

  • In-Rush Current

    • No limits but must specify the in rush current in the user documentation

  • Antenna Port Emissions

    • Required if the device has receiver antenna ports


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EN55103-2 IMMUNITY


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Immunity Tests (1)


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Immunity Tests (2)


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Performance Criteria

During immunity testing the product’s performance has to be assessed against various performance criteria:

  • Criterion A:

  • EUT should continue to operate as intended

  • Criterion B:

  • Degradation during the test but conformity with product specs after the test

  • Criterion C:

  • Degradation during the test and after the test. Conformity with product spec via user-intervention or automatic recovery. Replacement of fuses, or other repairs, does not constitute user-intervention


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Performance Criteria - Examples

Reduced signal-to-noise

Increased non-linearity distortion

Clicks and pops

Pitch variations

Intermittent muting

Change in gain

Change in operating mode (e.g. sample rate changes)

Examples of symptoms of lack of immunity for audio equipment are:


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ESD Immunity

  • EN61000-4-2

  • Performance Criteria B

  • ESD events create high-speed transients that can:

    • Permanently damage ICs

    • Cause false resets or other spurious reactions

    • The performance criteria is B - so some degradation in performance is permitted during the test but the device MUST recover without user intervention.

  • ESD events caused by people discharging directly to the product or to nearby objects


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    Radiated Immunity

    • EN61000-4-3

    • Performance Criteria A

    • The device is subjected to a radiated field from 80 - 1000 MHz

    • The field is amplitude modulated by a 1kHz tone

    • Simulates interference from radio (broadcast, walkie-talkie etc)

    • Products typically demodulate the 1kHz tone, creating interference on audio signal channels or on video displays


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    Conducted Immunity

    • EN61000-4-6

    • Performance Criteria A

    • Simulates interference on signal leads generated from AM and SW radio

    • A common mode interference signal is superimposed onto signal and power interface ports from 0.15 - 80 MHz

    • The signal is amplitude modulated by a 1kHz tone

    • Shielded signal lines have the noise directly coupled onto the shield


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    Fast Transients

    • EN61000-4-4

    • Performance Criteria B

    • Fast transients have a rise time of 5nS and width of 50nS

    • Simulates switching of inductive loads

    • They are applied in bursts

      • Bursts are 15mS long

      • Repetition rate of individual transients is 5kHz

      • Bursts occur every 330mS


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    Surge

    • EN61000-4-5

    • Performance Criteria B

    • The surge waveform simulates the transients induced onto the AC power line by lightning events

    • The wave-shape is 1.2/50 S open circuit voltage through a 2 ohm resistor (line to line) or 12 ohm resistor (line to ground). The short circuit current wave-form is 8/20S


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    Voltage Dips and Interrupts

    • EN61000-4-11

    • Simulates sags and brownouts in the AC supply voltage

    • Unit must self recover after a single cycle dropout (Criterion B)

    • Criterion C (user intervention permitted) for the 60%/100mS dip and 100%/5 second interruption


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    Magnetic Field Immunity 50Hz-10kHz

    • Test methods detailed in Annex A of EN55103-2

    • Criterion A

    • For Rack-Mount equipment, test level equals the limit for the emissions

      • (so this is to ensure immunity from other equipment)

    • Test method depends on installation

      • (rack-mount vs non-rack mount)

    • Specification details the construction of the loops

      • Possible to build the loops and perform tests in-house using an audio signal generator


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    Audio Frequency Common Mode

    • Test methods detailed in Annex B of EN55103-2

    • Required only for balanced signal/control ports that connect to cables longer than 10m

    • Annex B of the standard details the test circuit

    • Should be possible to test in-house

    • Performance should be detailed in user-manual


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    Design Techniques

    Although the next section concentrates on radiated emissions solutions, there is a reciprocity between emissions and immunity design techniques - the techniques that reduce emissions from a circuit can also reduce the amount of energy that is coupled into a circuit


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    Typical Problems

    • Products with digital circuits typically have problems meeting the emissions requirements

    • Products with predominantly audio circuitry typically have problems meeting the immunity requirements


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    Good Circuit Layout (1)

    Be VERY careful when splitting ground planes

    • Current flows in loops. The actual current path is the path of least IMPEDANCE

    • Large loops (relative to wavelength) create good radiating mechanisms to couple onto other signal traces

    • Fortunately at rf frequencies, return currents want to flow as close as possible to the signal current as this gives the path with least inductance and reduce the current loop - so provide the return path by routing fast signals next to power or ground planes.

    • NEVER let digital clocks cross splits in power planes - it forces current to flow in loops


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    Current Loops

    • Trace Crosses complete split


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    Current Loops

    • Trace Crosses split


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    Current Loops

    • No Split - no loop


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    Good Circuit Layout (2)

    • Keep clock lines as short as possible

    • Keep clock lines away from the edge of the board

    • Provide rf decoupling capacitors (ceramic, 0.01uF) on switching ICs located as close as possible to the IC

    • Decoupling caps are only effective to 100 MHz or so, above this frequency the best decoupling is achieved by having adjacent power and ground planes.

    • Clock lines should be terminated when they exceed 3” x tr to prevent ringing on the lines caused by reflections at either end of a line because the impedance of the trace  load/source impedance.

      tr = rise time in nS


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    Good Circuit Layout (3)

    • Provide filtering on all interface ports (including AC & DC power )

    • RF caps to a “clean” ground (typically chassis), common mode chokes or ferrite beads make ideal circuit elements

    • Include the filter components on ALL signal lines, including ground (especially where the ground is a digital signal ground)


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    I/O Interfaces

    • If possible, use PCB connectors with metal back shells as these can prevent high frequency signals radiated from the board from coupling onto the signal lines after the filter

    • Shields ideally terminate 360 to the enclosure (NOT to digital ground).

    • Shielded cables should have the shield terminated to the enclosure at the “noisy” end(s) - single ended grounding at rf does not work

    • Never use pigtails to terminate shields - at best they make a shielded cable ineffective, at worst they can increase emissions.

      • XLR cables are not designed for effective use of the shields - if you cannot terminate the shield directly to chassis (because of low frequency ground loops) tie to chassis using ceramic capacitors (alternatively create a capacitor on the PCB)


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    Enclosure Design

    • Required to reduce emissions above 250 MHz

    • Can help with ESD and other immunity problems

    • Slots and seams less than /10 (3cm @ 1GHz)

      • Select /10 based on

        • Highest clock speed

        • Preliminary test data

        • Previous product

    • Conductive finishes on metals

    • Good metal-to-metal contact (no paint !)

    • For low frequency emissions, consider using steel


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    AC Power Supply

    • Just because a power supply is CE-marked does not indicate that it meets any emissions (or immunity) limits - but it should indicate that it meets an appropriate LVD (electrical safety) standards.

    • If the vendor specifies that an RFI filter is required, use one

    • When using filters, make certain that the metal case is bonded to the enclosure.

    • Do not route the output wiring from the filter past any circuits, the wiring should exit the enclosure immediately to prevent noise coupling back onto the AC wiring.


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    Circuit Board

    P/S

    Filter

    On/Off

    AC Power Supply

    AC Wiring layout to power supply via filter - good layout and bad layout Examples


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    On/Off

    Filter

    Circuit Board

    P/S

    AC Power Supply

    AC Wiring layout to power supply via filter - good layout


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    Immunity Solutions (1)

    • ESD

      • Filtering I/O lines

        • L-C circuits reduce common mode noise coupled into receivers

        • Transzorbs (or similar devices)

          • Fast switching times required - the rise time of ESD test signal is typ. < 1nS

          • Device clamps input signal to a maximum level, preventing damage to inputs of ICs

    • Good enclosure design

      • Re-direct the ESD current away from circuitry


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    Immunity Solutions (2)

    • ESD continued...

      • Problems can be solved in software

        • By regularly re-setting input buffers

          • One example is a software driver for a mouse that empties the serial input buffer to prevent the mouse from locking up

        • By polling devices to ensure they are still active

        • By averaging data - throw away data samples that are unexpected and average remaining samples.


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    Immunity Solutions (3)

    • Radiated Immunity

      • Solve problems in a similar manner to radiated emissions

      • Restrict bandwidths

      • Add common mode filtering to audio inputs

      • Pay particular attention to high-gain stages - make sure they are provided with adequate rf decoupling

    • Fast Transients

      • Transzorbs on I/O lines, filtering, enclosure design all have an effect

    • Surge

      • Power supply design could incorporate MoVs line-to-line (line-to-ground typically prohibited by Safety standard)

      • AC line filters can reduce surge effects.


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    Emissions Case Study

    • Product failing emissions below 150 MHz. Long clock lines on a back plane-style circuit board inside aluminum enclosure failing at 150 MHz

    • Signals were radiating from internal back-plane out of the chassis and from shielded interface cables connected outside of the chassis


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    The fixes……….

    • Had to remove non-conductive coating from the aluminum panels where they touched each other

      • Problem - aluminum oxide is non-conductive and it oxidizes quickly. Within a couple of days the emissions were high again and had to remove oxide layer.

    • Improved enclosure’s rf integrity using a conductive coating and gaskets to ensure good metal-to-metal contact

    • Added series termination to clock lines to reduce problem at board level

    • Improved grounding of the interface cable shields by improving contact between connector shells and enclosure


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    EMC As Part Of The Development Cycle

    Don’t leave EMC until the end !


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    • Remember EMC at the start of the project

      • Define the intended environment so that the immunity levels and emissions limits can be identified

        • E1 - E3 require 10dB lower radiated emissions that E4 and E5

        • E4 has lower immunity test levels

      • Specify EMC requirements on external vendors based on the intended environment (e.g. power supplies)


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    Test prototype boards ( Emissions/ESD)

    Emissions tests:

    RF current probes can be used to measure common mode current on I/O cables in-house (refer to Ott, Chapter 11)

    Keep common mode current below 15uA at any frequency for Class A, 5uA for Class B

    If local test labs have chambers, get a “quick”scan of boards in the development stage (typically < 2 hours per test)


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    • Identify potential immunity problems :

      • if the unit passes ESD with no errors, that is a good indication that the unit will not be susceptible to most of the EMC phenomena.

      • ESD guns cost about $6,000 (Schaffner / Keytech)

      • Can be rented (Metric / Telogy)


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    • Use emissions/immunity preliminary data:

      • the enclosure can be designed to provide adequate shielding

      • enclosure design can be based on the highest significant emissions observed during the preliminary scans

      • filters can be placed on interface ports to reduce common mode noise

      • grounding strategies can be evaluated


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    Summary

    • Professional audio equipment has many EMC test requirements compared to generic products

    • It is possible to perform some of the tests in-house without spending $$$$

    • It will probably be necessary to perform some tests at a test lab

    • If EMC is taken into consideration at the start of the project time-to-market is reduced and re-design costs are minimized.


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    Literature References

    • The Guide to The EMC Directive

      Chris Marshman, IEEE Press

    • Noise Reduction Techniques in Electronic Circuits

      Henry Ott, John Wiley

    • High Frequency Measurements and Noise in Electronic Circuits

      Douglas Smith, Van Nostrand Reinhold

      Magazine subscriptions:

      Compliance Engineering

      Evaluation Engineering


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    EMC Test Equipment

    • Fischer Custom Communications

      • [email protected]

      • Current probes for making common mode emissions measurements (150kHz - 300 MHz)

      • LISNs for making conducted emissions measurements on AC

  • Agilent

    • Spectrum Analyzers (8595EM analyzer)

  • Haefely

    • Immunity test equipment

  • Schaffner

    • Immunity test equipment


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    Please provide feedback about the presentation:

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    Visual Aids 5 4 3 2 1

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