Electromagnetic Interference with Electronic

Journal of Medical Systems, Vol. 24, No. 1, 2000
Electromagnetic Interference with Electronic Medical
Equipment Induced by Automatic Conveyance Systems
Eisuke Hanada,1,3 Yoshiaki Watanabe,2 and Yoshiaki Nose1
Electromagnetic interference (EMI) with electronic medical equipment induced by
automatic conveyance systems is estimated. We measured the electric intensities of
electromagnetic waves transmitted by three self-controlled electric truck systems. We
also observed EMI with an infusion pump and a syringe pump set 1 m from the rail.
The maximum electric field intensity was observed at the supplied current frequency
in two systems with non-contact power supply mechanisms. The highest value, 137.0
dB애V/m, was measured just beside the rail. This is higher than the international
electromagnetic immunity standard limit for electronic medical equipment. EMI may
occur if electronic medical equipment is used within 2 m of the rail when the system
contains an inductive power supply mechanism. With a contact power supply mechanism, the electric field intensity was much lower than that of the immunity standard.
EMI should not occur even when electronic medical equipment is used just beside
the rail.
KEY WORDS: automated conveyance system; electromagnetic fields; electromagnetic interference;
electronic medical equipment; non-contact power supply mechanism.
INTRODUCTION
Automatic material conveyance systems, which are commonly used in factories
and storehouses, are now being introduced into large hospitals.(1–3) Some systems
transmit high intensity electromagnetic waves, and ways to avoid electromagnetic
interference (EMI) should be carefully considered.(4–6) For example, some systems
contain non-contact power supply mechanisms and a linear motor. If the system
generates a strong intensity electric field, EMI with electronic medical equipment
may occur. To determine the safety of these systems, we measured the electromagnetic field intensity around three types of automatic conveyance system.
1
Department of Medical Information Science, Graduate School of Medical Science, Kyushu University.
Department of Information Science, Faculty of Science and Engineering, Saga University.
3
To whom correspondence should be addressed at: Department of Medical Information Science, Graduate School of Medical Science, Kyushu University, Maidashi 3-1-1, Higashi-ku, Fukuoka, 812-8582 Japan.
2
11
0148-5598/00/0200-0011$18.00/0  2000 Plenum Publishing Corporation
12
Hanada, Watanabe, and Nose
Fig. 1. Power supply construction of ‘‘Autran Vanguard.’’
METHODS
We measured the electric field intensity of each subject system as shown in
Table 1. Test line conditions are also shown in Table I. Each subject system is a
full-scale test system located in the distributor’s plant. Equipment used in each
measurement is shown in Table II. Other factory machines were stopped to avoid
electromagnetic noise.
The structure of the Autran Vanguard system and the antenna positions are
shown in Figs. 1 and 2. ‘‘Autran Vanguard’’ has a non-contact-type power supply
Table I. Subject Systems and Their Test Line Conditions
System
Distributor
Rail material
Rail figure (max
thickness)
Power-feed
architecture
Truck motor
Carrying capacity
Maximum speed
Test line location
Power supply (at the
measurement)
Surroundings
Construction material
of the shed
Floor material
Meteorological
conditions (ave.)
Autrun Vanguard
Super Limliner F3
Tsubakimoto Chain
Co.
Aluminum
H figured (15 mm)
Shinko Electric Co., Ltd.
Aluminum
Box (7 mm)
Noncontact (IPF)
Noncontact (IPF)
Induction motor
70 kg
50 m/min
Tsubakimoto Chain
Co. Hyogo plant
Linear direct motor
15 kg
180 m/min
Shinko Electric Co., Ltd.
Electronic products &
Control Systems Works
9.6 kHz, 40.0 A,
(200 V ave.)
Green Beld and Road
Steel-frame slate panels
12.2 kHz, 42.5 A,
(200 V ave.)
Green Belt
Steel-frame slate
panels
Steel with skid
protection
Cloudy, 19⬚C, 60%
SIMACOM-LDM
Siemens K.K.
(Japan)
Aluminum
U figured (4 mm)
Contact (collector
brush)
Linear direct motor
15 kg
120 m/min
Siemens K.K.
Katsushika office
Concrete
60 Hz, 0.7 A/truck,
200 V
Residential houses
Steel-frame slate
panels
Concrete
Cloudy, 28⬚C, 85%
Clear, 32⬚C, 60%
Electromagnetic Interference by Automatic Conveyance Systems
13
Table II. Measurement Equipment and Its Settings
Measurement of system A
Type of equipment
Field strength meter
Field strength meter
Loop antenna
Dipole antenna
Type
ML428B
ML518A
MP414B
MP534A
ML428B settings
Pass band: 0.2 KHz (10 앑 150 KHz)
9 KHz (150 KHz 앑 30 MHz)
DET (mode): Peak hold(s): 3 sec
Measurement of system B
Type of equipment
Type
Spectrum analyzer
R3265
Loop antenna
HFH2-Z2
Attenuator (6 dB)
MP721A
R3265 settings
Bandwidth: RBW 1 kHz, VBW 10 KHz
Sweep: 100 ms
Measurement of system C
Type of equipment
Type
Field strength meter
ESH3
Field strength meter
ESV
Loop antenna
HFH2-Z2
Bi-conical antenna
BBA9106
Log-periodic antenna
UHALP9107
ESH3 settings
Pass band 0.2 KHz (9 앑 150 KHz)
9 KHz (150 KHz 앑 30 MHz)
Mode: CISPR 16-1
Distributor
Anritsu
Anritsu
Anritsu
Anritsu
Frequency in use
10 kHz 앑 30 MHz
50 MHz 앑 500 MHz
10 kHz 앑 30 MHz
30 MHz 앑 500 MHz
ML518A settings
Pass band: 120 KHz
DET (mode): Peak hold(s): 3 sec
Distributor
Advantest
Rohde & Schwarz
Anritsu
Frequency in use
1 kHz 앑 300 MHz
9 kHz 앑 30 MHz
Distributor
Rohde & Schwarz
Rohde & Schwarz
Rohde & Schwarz
Schwarz beck
Schwarz beck
Frequency in use
10 kHz 앑 30 MHz
30 MHz 앑 1000 MHz
10 kHz 앑 30 MHz
30 MHz 앑 300 MHz
300 MHz 앑 1000 MHz
ESV settings
Pass band: 120 KHz
Mode: CISPR 16-1
mechanism (inductive power feeder, IPF). The power source for the trucks is an
induction motor. In IPF, an alternating electric current is supplied to the power
line that induces an alternating magnetic field around the power line. Coils set on
the trucks are located in the magnetic fields, and the alternating magnetic fields
generate alternating current in the coils. With this architecture, trucks obtain electric
power from the power line without contact.
Because of lack of space to set the antennas outside the test line, Points A
and B were set on the vertical line at the center of the parallel rails where the
electric intensity seemed to be maximum. The height of Point B was determined
in relation to rail height and antenna size.
Measurements were taken with the truck running in the location nearest the
antenna and with the system switched OFF. The value of generated electric field
intensity was the subtraction of the two results measured at the same frequency.
The measurement frequencies ranged from 10 kHz to 500 MHz.
The structure of the Super Limliner F3 system and the antenna positions are
shown in Figs. 3 and 4. ‘‘Super Limliner F3’’ has IPF in the power-feed mechanism
and a Linear Direct Motor (LDM) as the power source of the trucks. In LDM,
permanent magnets are lined-up on the rail with polarization alternating. Direct
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Hanada, Watanabe, and Nose
Fig. 2. ‘‘Autran Vanguard’’ test line form and measurement points.
current is supplied to the coil on the truck, and the coil is forced to move by
Fleming’s left-hand rule.
Because of the structure of the truck, which covers the rail, we measured with
no trucks running near the antenna for Points A, B, and C. For Point D, we
measured with a truck in the station.
In this measurement, we first checked the frequency distribution of electric
intensity by spectrum analysis, then measured the highest electric intensity using
an intensity meter. The analyzed frequencies ranged from 1 kHz to 1 MHz.
The SIMACOM-LDM system structure and the antenna positions are shown
Fig. 3. Power supply construction of ‘‘Super Limliner F3.’’
Electromagnetic Interference by Automatic Conveyance Systems
15
Fig. 4. ‘‘Super Limliner F3’’ test line form and measurement points.
in Figs. 5 and 6. ‘‘SIMACOM-LDM’’ has a contact-type power supply mechanism
and LDM. In contact type power supply mechanisms, the current collector on the
trucks, a brush or bar, is continuously in contact with and sliding on the power
line, and the trucks obtain current through the collector.
In each measurement, we measured with a truck running in the location nearest
the antenna. We also measured background electromagnetic noise. The measurement frequencies ranged from 10 kHz to 700 MHz.
Fig. 5. Power supply construction of ‘‘SIMACOM-LDM.’’
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Hanada, Watanabe, and Nose
Fig. 6. ‘‘SIMACOM-LDM’’ test line form and measurement points.
We observed whether or not EMI occurs with an infusion pump (Terumo TE112) and a syringe pump (Terumo STC-525). Both pumps have electromagnetic
immunities required by international electromagnetic immunity standard IEC606011-2.(8)
For each pump, we simulated operating conditions using 0.9 % salt water. The
amount of liquid flow was set at 60 ml/h for the infusion pump and 10 ml/15 min
for the syringe pump. After running each pump for 15 min, we measured amount
of liquid flow. For testing the Autran Vanguard system, the two pumps were located
at Point A in Fig. 2, and a truck was set near the pump. For the Super Limliner F3
system and the SIMACOM-LDM system, the pumps were located at a measurement
point in front of the station (Point D in Fig. 4, and Point C in Figure 6), and a
truck was set in the station. The pumps were suspended on a stand.
RESULTS
The results for the Autran Vanguard system are shown in Fig. 7. The results
of spectrum analysis at Point A for the Super Limliner F3 system are shown in Fig.
8. The results for the SIMACOM-LDM system are shown in Fig. 9. In Fig. 9, the
values include background noise. The maximum electric field intensities at each
measuring point are shown in Table III.
No interference, such as a sensor error or irregular equipment stop, was observed. The liquid flow of each observation was within 0.2 ml of the setting, within
the permitted difference as written in their equipment instructions.
Electromagnetic Interference by Automatic Conveyance Systems
17
Fig. 7. Electric intensity with ‘‘Autran Vanguard.’’
DISCUSSION
Although it is possible to measure both electric and magnetic fields intensity,
we measured only electric field intensity because the electromagnetic immunity
Fig. 8. Frequency distribution of electric intensity with ‘‘Super Limliner F3’’ (Point A).
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Hanada, Watanabe, and Nose
Fig. 9. Electric intensity with ‘‘SIMACOM-LDM.’’
of electronic medical equipment has been standardized internationally with this
parameter. When measuring electric and magnetic field intensities, measurement
in an anechoic chamber is encouraged, because the anechoic chamber eliminates
electromagnetic waves coming from outside, prevents reflection from walls and
floors, and stabilizes measurement results, all of which increase accuracy. However,
it was impossible to use an anechoic chamber for this study because of the size of
the subject system.
International standards IEC60601-1-2(7) and IEC61000-4-3(8) say that electronic
medical equipment should run normally in electromagnetic fields of 3 V/m electric
intensity. Our results indicate that there are some areas where electric field intensity
is over 3 V/m (129.54 dB애V/m) near IPF systems. The contact-type power supply
mechanism, LDM and the induction motor do not seem to cause EMI.
There is no international electromagnetic immunity standard for frequencies
under 28 MHz or over 1 GHz. If the frequency range of the international standards
Table III. Maximum Values and Frequencies of Maximum Intensities
Autran Vanguard
Point
Point
Point
Point
a
A
B
C
D
1.55,
0.47,
7.08,
1.16,
12.2
12.2
12.2
12.2
Super Limliner F3
1.05,
0.91,
2.00,
2.19,
9.6
9.6
9.6
9.6
SIMACOM-LDM
0.15, 30.0
0.35, 190.0
0.52, 550.0
—
Values are the maximum electromagnetic intensity (V/m), and the frequency of
maximum intensity (kHz).
Electromagnetic Interference by Automatic Conveyance Systems
19
were extended, there might be EMI with electronic medical equipment located
close to IPF systems. Electric intensity in the ‘‘far region’’ is said to be in inverse
proportion to the distance from the origin. But, in measuring the Autran Vanguard
and Super Limliner F3 systems, we found all points to be in the ‘‘near region,’’ at
about 10 kHz or lower frequency electric field. In this situation, the relationship
between the electric field intensity and distance is not in inverse proportion. Keeping
sufficient distance, more than 2 m between electronic medical equipment and truck
systems, is the most effective way to prevent EMI. Within 2 m, electric field intensity
increases and may be over 3 V/m. But as we reported,(9) reflections or transparency
of electromagnetic fields at walls, ceilings, and floors should be considered. To
reduce the possibility of EMI from the truck system, electromagnetic shielding
materials should be arranged around the system. Electromagnetic conductive materials can also be set on walls and ceilings to prevent reflection. Decreasing the
current feeding into the power line would reduce emission; however, decreasing
the current means decreasing the power, which would decrease the speed and
carrying capacity of the trucks. Since efficient electromagnetic shielding against 10
kHz band radio waves is difficult, electronic medical equipment should be kept
more than 1 m from a rail.
In maintaining conveyance systems, hospital directors should also consider the
container handling stations. In the Super Limliner F3 and SIMACOM-LDM systems, power supply lines are located on the rail in the station and electric current
is continuously supplied. Keeping patients at least 2 m away from stations or a
mechanism to prevent opening of the station covers by patients would be necessary
to avoid EMI.
ACKNOWLEDGMENTS
The authors wish to thank Tsubakimoto Chain Co., Shinko Electric Co., Ltd.,
and Siemens K.K. for providing test lines and preparing measurement equipment
for this study. The authors also wish to thank A-PEX International Co., Ltd. and
Japan Quality Assurance Organization for supporting us. This study was supported
by grants-in-aid from the Japan Society for the Promotion of Science (No.10771331).
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