Analog Devices AN529 Application Notes
AN-529
a
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APPLICATION NOTE
5B Series Signal Conditioning Subsystems
in RFI/EMI Fields
The 5B Series Signal Conditioning Subsystem has been
tested and passed the stringent “heavy industrial” requirements of the European Union’s electromagnetic
compatibility (EMC) directive.
In order to comply with the European Standards in a
typical heavy industrial application we recommend the
following setup:
1. The modules must be mounted on a standard 5B
Series backplane.
2. The 5B backplane must be mounted inside a standard
metal cabinet that fully encloses the modules on all
sides. The cabinet must be earth grounded at a convenient point and good electrical contact between all
side panels must be assured.
3. All wiring must be routed through a metal conduit or
wire chase (flexible or rigid).
4. The conduit must be earth grounded and electrically
connected to the cabinet.
5. Due to the low input levels, it is recommended that all
input, output and power lines be shielded.
When used according to these installation directions,
any errors caused by EMI/RFI interference will be less
than 0.1% of the full-scale 5B measurement range (typical @ +25°C), for field strengths up to 10 V/m and frequencies up to 1 GHz.
CE CERTIFICATION TESTS
The 5B Series modules have been tested and certified
according to the rigorous electromagnetic constrains of
the EN50082-2 and EN50081-2 European Standards. A
description of each test is given below, followed by
Table I listing the standards for each test.
Test Descriptions
1. Radiated RF Immunity
The units were subject to an RF field using a log-periodic
antenna, maintained at 10 V/m by an amplifier placed
outside the RF chamber. The field was swept from a frequency of 80 MHz to 1 GHz, with a 1 kHz modulation. The
frequency increment size was 0.2% of the current frequency and the settling time at each frequency was two
seconds. The field strength was supervised by an RF
field monitor located next to the cabinet holding the
units. The amplifier was adjusted accordingly to maintain the 10 V/m field strength. The antenna was placed
exactly 1 m from the units. Readings were taken for both
horizontal and vertical polarizations. The outputs of the
units under test were acquired at every frequency
through a crosspoint matrix scanner and a precision
digital voltmeter. By subtracting the baseline reading
taken with no RF field, the change was obtained and
then expressed and stored as a percentage of span
change. This test simulated the effect of system operation in an environment that is exposed to strong (heavy
industrial) radiated electromagnetic waves.
SENSORS
POWER
SUPPLY
CONTROL
SYSTEM
Figure 1. General Wiring Configuration
FLEXIBLE/RIGID
METAL CONDUIT
BACKPLANE
METAL CABINET
2. Conducted RF Immunity
The units were subject to conducted EMI via an RFgenerated signal resistively injected into the conductive
5B
layer of a standard flexible wire chase housing the wires
from the system backplane. The point of contact was approximately 20 cm from the units. The field was swept
from a frequency of 150 kHz to 80 MHz, with a 1 kHz
modulation. The frequency increment size was 1% of the
current frequency and the settling time at each frequency was two seconds. Ferrite beads were placed outside the RF chamber on the wires to ensure that the
disturbance was not reflected to the test measurement
instrumentation. As in the radiated RF immunity tests,
the outputs of the units were scanned in and the percentage of span change was stored.
AN-529
3. Fast Transient Immunity
All field wires external to the system console are subjected to and must withstand transients occurring within
the normal environment of operation. The test configuration, routing field wires through a single wire chase,
requires transient testing be applied to the wire chase;
thus the conduit carrying the wires were placed in a
metal enclosure for testing. Positive and negative polarities of 0.5 kV, 1 kV and 2 kV with 5 ns/50 ns rise/fall times
were capacitively injected into the conduit. The outputs
were scanned before and after the transients and the
percent of span change was calculated and stored. (The
test instrumentation and supporting test equipment
were removed from the proximity of the wires during
the application of the transients to avoid damage to the
test equipment.)
4. Pulsed RF Immunity
The units were subjected to radiated RF at 900 MHz,
10 V/m, 100% square wave modulated at 200 Hz inside
the RF chamber using a log-periodic. About 180 readings were taken with a settling time of two seconds for
each reading. Both vertical and horizontal polarization
were tested. Once again, the percentage of span change
was calculated and stored.
5. Magnetic Field Immunity
The units were placed within two coils carrying current
to generate a magnetic field of 30 A/m @ 50 Hz. The field
strength was measured using a loop antenna and an oscilloscope. The units were placed in three configurations, X, Y and Z relative to the magnetic field. The
outputs of the units were scanned and the percentage of
change calculated. This tested the units’ behavior under
stray magnetic fields.
6. ESD—Contact
The units were subjected to the contact method following the human model by an ESD gun four times, using
positive and negative polarities at 4 kV. The ESD was
applied to the units’ cases, mounting screws and the DB25 connector backshell. After exposure, the units were
retested to ensure proper functionality.
7. ESD—Air
The units were subjected to the air discharge method
following the human model by an ESD gun eight times,
using positive and negative polarities at 2 kV, 4 kV, 6 kV
and 8 kV. The ESD was applied to the units’ cases,
mounting screws and the DB-25 connector backshell. After exposure, the units were retested to ensure proper
functionality.
8. Voltage Surges Immunity
Five positive and five negative 2 kV pulses with
1.2 µs/50 µs. Its rise/fall times, each lasting 1 minute,
were applied directly onto the shields at the input end of
the field wiring. A capacitor was connected from shield
to ground near the module end of the field wiring. When
a particular shield was under test, it was ensured that its
shield did not contact any other shields, forcing the
surge to enter the unit. The units were retested after
exposure to ensure proper functionality.
9. Emissions
The units were tested for radiated and conducted emissions. The units were biased at maximum output and
readings of field strength from 30 MHz to 1000 MHz in
both vertical and horizontal polarization were taken.
Readings from the ac main of the dc power supply from
50 kHz to 30 MHz were also taken.
E3279–5–3/98
Table I. List of Test
No. Test Test Specification Basic Standard Test Setup Criteria
1 Radiated RF Immunity 800 MHz–1000 MHz, 10 V rms, ENV 50140 ENV 50140 A
Modulated, 1 kHz, 80%
2 Conducted RF Immunity 0.15 MHz to 80 MHz, 10 V rms ENV 50141 ENV 50141 A
80% Amplitude Modulated (1 kHz)
3 Fast Transient Immunity 1 kV, 2 kV IEC 801-4 IEC 801-4 B
4 Pulsed RF Immunity 900 MHz, 50% Duty Cycle , 200 Hz ENV 50140 ENV 50140 A
5 Magnetic Field Immunity 50 Hz, 30 A/m EN 61000-4-8 EN 61000-4-8 A
6 ESD Immunity Contact 4 Contact EN 61000-4-2 EN 61000-4-2 B
7 ESD Immunity Air 8 Air Discharge EN 61000-4-2 EN 61000-4-2 B
8 Voltage Surge Immunity 2 kV, 5 Positive, 5 Negative B
9 Emissions Radiated and Conducted
–2–
PRINTED IN U.S.A.
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