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Indigenous development of medical electrical safety analyzer
Article · May 2011
DOI: 10.1109/MeMeA.2011.5966675
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Indigenous Development of
Medical Electrical Safety Analyzer
Jiju. K
Power Electronics Group, CDAC-T
Thiruvananthapuram, India
jijuk@cdactvm.in
Dr. Niranjan D. Khambatte
Instrumentation Laboratory, SCTIMST
Thiruvananthapuram, India
niranjan.d.khambete@gmail.com
Sreekumari. B
Power Electronics Group, CDAC -T
Thiruvananthapuram, India
sreekumarib@cdactvm.in
Abstract—In order to achieve the required high level of electrical
safety of electro-medical equipment, regulatory bodies worldwide
have developed standards and guidelines to control their design
as well as their use in hospitals and other health care delivery
settings. It is highly essential that periodic preventive
maintenance and electrical safety checks on all electro-medical
equipment in use be carried out and records of these be
maintained. International standard for routine testing of medical
equipments at hospitals and clinics is International Electro
technical Commission (IEC) 62353[1]. This paper deals with the
design and development of an indigenous Medical Electrical
Safety Analyzer, which will conduct safety tests as per this
standard. The safety tests like Earth bond test, Leakage current
and Insulation tests to be conducted as per the standard are also
discussed.
Keywords- Medical Electrical Safety Analyzer, IEC 62353
I.
INTRODUCTION
Electrical Safety is one of the most important parameters of
electro-medical equipment. The manufacturer of such
equipment would design, fabricate, and test their equipment as
per the International standards (IEC 60601) or Indian Standards
(IS 13450) and obtain certification from appropriate regulatory
agencies before supplying the equipment to the hospitals. The
standards and guidelines also strongly recommend that hospital
administration carry out inspection and electrical safety testing
on all the incoming equipment to rule out any damage during
transit that might compromise safety. In future use, the
equipment can become unsafe due to deterioration of insulation
either accidentally or through normal weathering process of the
material. Therefore, in order to assess the level of electrical
safety of the equipment, it is essential that hospital staff carries
out periodic safety testing on all the electro-medical equipment
(EME) in use. In May 2007, IEC has published a safety
standard for the periodic testing of medical equipments in
hospitals. This standard is termed as IEC 62353. Clinical
engineers or testing agencies can effectively and conveniently
carry out this task using a handy and portable Electrical Safety
Analyser (ESA).
This general safety for medical electrical equipment is
necessary because of the particular relationship of such
equipment to the patient, the operator and the surroundings.
978-1-4244-9338-8/11/$26.00 ©2011 IEEE
The following aspects play an important role in this
relationship:
i. The inability of patient or operator to detect the
presence of certain potential hazards, such as
ionizing or high frequency radiation
ii. Absence of normal protection to currents provided
by the patient's skin, if this is penetrated or treated
to obtain a low skin resistance
iii. Absence of normal reactions of the patient who
may be ill, unconscious, anaesthetized,
immobilized etc
iv. Support or replacement of vital body functions
may depend on the reliability of the equipment.
v. The simultaneous connection to the patient of
more than one piece of equipment.
vi. Combination of high power equipment and
sensitive low-signal equipment often in ad-hoc
combinations.
vii. The application of electric circuits directly to the
human body, either through contacts to the skin
and/or through the insertion of probes into internal
organs.
viii. Environmental
conditions,
particularly
in
operating theaters, may present a combination of
humidity, moisture and/or fire hazards caused by
air, oxygen or nitrous oxide combined with
anesthetic media and cleaning agents.
II.
CLASSIFICATION OF MEDICAL EQUIPMENT
A. According to the type of protection against electric shock
a) Equipment energized from an external electrical power
source:
i. Class I equipment: - Equipment protection against
electric shock by additional protection to basic
insulation through means of connecting exposed
conductive parts to the protective earth in the fixed
wiring of the installation.
ii. Class II equipment: - Equipment in which
protection against electric shock does not rely on
basic insulation only, but in which additional safety
precautions such as double insulation or reinforced
insulation are provided, there being no provision for
protective earth or reliance upon installation
conditions.
b) Internally powered equipment.
B.
According to the degree of protection against electric
shock
i. Type B equipment: - Equipment providing a
particular degree of protection against electric
shock, particularly regarding allowable
leakage current and reliability of the protective
earth connection
ii. Type BF equipment: - Type B equipment with
floating type applied part (F-type applied part)
iii. Type CF equipment: - Equipment providing a
degree of protection higher than that of BF
equipment against electric shock particularly
regarding allowable leakage currents, and
having an F- type applied part. Equipment
intended for direct cardiac applications shall be
of CF type
III.
TESTS ACCORDING TO IEC 62353
The main tests to be conducted are
i. Earth bond test
ii. Insulation resistance measurement
iii. Leakage current measurements
Earth bond test : This tests the integrity of the low
resistance connection between the earth conductor and any
metal conductive parts, which may become live in case of a
fault on CLASS I medical devices. The normal resistance value
is in milliohms. A constant current signal is applied to the
Device Under Test (DUT) for this test.
Insulation resistance measurement : Measures the
insulation resistance between the mains and various points of
the medical equipment, which may come into contact with
patient/user.The normal range is in megohms. A test signal of
500 volt DC is applied to the DUT.
be shoted and an equivalent voltage generated by the analyzer
will be connected as prescribed in the standard.
For all these tests different categories are there and all
together 23 tests can be done with the system.
IV.
PASS/FAIL LIMITS OF IEC 62353
The pass fail limits of the standard are provided below.
TABLE I.
PASS/FAIL LIMITS OF IEC 62353
Earth bond resistance measurement
Equipments with non-detachable power cord
0.3 Ω
Equipments with detachable power cord
0.2 Ω
Insulation resistance measurement
Insulation resistance in all Should be > 0.1 M Ω
measurements
Leakage current measurement (RMS in mA)
Equipment
Type
Type B
Type BF
Applied
Applied
Part
Part
Equipment Leakage – Alternative method
Type CF
Applied
Part
Class 1
1
1
1
equipment
Class 2
0.5
0.5
0.5
equipment
Equipment Leakage – Direct or differential method
Class 1
0.5
0.5
equipment
Class 2
0.1
0.1
equipment
Patient Leakage current – Alternative method
0.5
0.1
Class 1 & 2
0.05
Patient Leakage current – Direct method
0.05
Class 1 & 2
0.05
0.05
V.
PRINCIPLE OF OPERATION
The equipment under test is to be connected to the analyzer
and the test parameters are measured by applying test signals,
according to the standard.
Leakage current measurement : Measures the leakage
current passing through the earth conducter or the patient
connections. The normal range values are in milli/micro
amperes. As per standerd the system can test different leakage
currents in different conditions, they are
Direct method: Measures true leakage that would occur
whilst the medical equipment is in typical use, this will give
highest accuracy on low leakage current measurement. The
DUT will be powered ON from mains through the analyzer.
Differential method: Measures the total leakage current
and DUT does not need to be isolated during measurement.
The DUT will be powered ON from mains through the
analyzer and the measurement is taken as the difference
between line and neutral currents.
Alternative method: This test provide highest safety for
person doing the test. Here the supply inputs of the DUT will
DUT
ESA
Figure 1. Connection between Device Under Test (DUT) and Electrical
Safety Analyzer
During safety testing the DUT is to be powered from the
analyzer. All patient leads should also be connected, in order to
measure the leakage currents. The analyzer conducts tests
either manually or automatically and displays the results for
each test. All test signals are generated by the analyzer and
applied to the DUT and measurements are taken from the
corresponding test points.
VI.
SYSTEM DESIGN & ARCHITECTURE
The developed system having mainly three parts, they are
power supply module, a controller PCB and a Relay PCB. The
controller used is PIC microcontroller. Various relays are used
to apply test signals required for the tests and to take
measurements from the corresponding points. The
measurements are done with a digital multi meter IC having
22000 counts resolution.
The microcontroller interface with the measurement circuits
is through a serial data link, by which it can accept the
measured data for processing. The user interface is through an
LCD/Keypad combination or through a PC. The test voltages
are generated by the power circuits according to the
requirements of the standard.
Figure 3. Block diagram of Controller PCB
Signal amplifier & Gain controller: This circuit amplifies
low voltage sine wave generated by programmable wave form
generator and its gain is controlled.
CPLD & Relay driver: To reduce the hardware volume and
for the design flexibility the digital logic circuits are
implemented with a 100 pin CPLD chip. Darlington Transistor
Array drivers are used for driving relays.
Instrumentation circuit: A high accurate (22000 counts
resolution) digital multi meter IC used in measurements
circuit.
Figure 2. System architecture of Medical Electrical safety Analyzer
Figure.2 shows how the medical electrical safety analyzer is
implemented. The power supply module generates the supply
voltages for the PCBs. The relay PCB contains various relays
for applying the input signals and for measurement of
parameters from different points. The controller PCB contains
the PIC microcontroller and its associated circuits. The
LCD/Keypad interface enables the user to select the tests and
view the measurements, test pass/fail status etc. The PC/Laptop
interface provides data logging to record the test results of
various equipments through USB. A Bluetooth interface is
provided for remote operation by Mobile/ PDA. A test probe
can be connected to touch the DUT parts as and when required
for various tests.
Figure 3 shows the functional block diagram of controller
PCB. PIC18F4550 is the brain of the system. The controller
PCB is having six other functional modules as given below.
Communication drivers: It contains serial communication
drivers and its related circuitry for TTL to RS232C conversion.
Sine wave generator: It is a programmable wave form
generator based circuit configured to produce 50Hz sine wave.
Figure 4. Block diagram of Relay PCB
Figure 4 briefly explains the main functional blocks in
Relay PCB, having the following circuit modules
Constant current source: This will generate a constant current
above 200mA for Earth Bond test.
Current sensor: A Hall Effect current sensor is used for high
accuracy measurement of leakage current.
Rectifier: A bridge rectifier is used for generating 500VDC for
insulation measurement.
Body model: It is the electrical equivalent of human body as
per IEC standard.
Power amplifier: Class AB power amplifier used for power
amplification of sine wave.
Transformer: It is a low frequency step-up transformer to
boost sine wave voltage to generate 250VAC and 500VDC.
VII. TEST SIGNALS GENERATION
i. 12V, 210 mA for Earth bond test (Constant
current source).
ii. 500 V DC, 0.1 mA for Insulation resistance
measurement.
iii. 250 V AC, 50Hz for leakage current
measurement (Alternative method)
communication algorithms. It also handle data processing and
manipulation.
VIII. MEAUREMENTS
The measurements are taken from various points of the DUT
according to the test requirements. For measuring leakage
currents, a human body model (MD) is required and its
electrical equivalent circuit is shown in Figure 5
R1
Z
C1
R2
V
Voltage
Measuring
Instrument
R1 = 10kΩ ± 5%, R2 = 1kΩ ± 5%, C1 = 0.015μF ± 5%
Figure 5.
IEC Body Model (1kΩ)
Figure 7.
A typical test configuration for measuring applied part leakage
current using direct method is shown in Figure 6.
Controller software algorithm
X.
FEATURES
i. Referred standard : IEC 62353
ii. Measurement resolution : 22000 counts
iii. User interface : Graphical LCD and keypad
iv. Other optional interfaces : USB and Bluetooth
v. Utility software supporting OS : Windows and
Linux
XI.
Figure 6. Measuring circuit for the measurement of Applied Part Leakage
Current for Class I - Direct Method
Appropriate combinations of relays are switched under the
control of software for applying the input signals and for taking
measurements from the DUT, as per the requirements of each
and every test.
IX.
PERFORMANCE ANALYSIS
The proto models of the system are tested and
evaluated against IEC 62353 standard requirements in a
national accreditation laboratory. Measurements are
compared with those taken by a high precision standard
(Agilent U1252A) digital multi-meter, having resolution of
50000 counts. This comparison will show the accuracy of
developed Medical Electrical Safety Analyzer in
measurements.
CONTROL SOFTWARE
The embedded software developed with C language in
MPLAB IDE with Microchip’s C18 compiler. PC side
graphical user interface is developed with C# in Microsoft
Visual studio 2008 for windows and Glade GUI tool for
Linux. For in-circuit programming of the CPLD, Altera’s
Quartus II 9.0 IDE is used.
Figure 6 shows the simple flow of controller software. It is
written in C language and compiled with Microchip’s C18
compiler. This software contains LCD, USB and other serial
TABLE II.
MEASUREMENT COMPARISON
Developed system
Standard DMM
Earth Bond Resistance (Ω)
0.3933
0.390
0.5624
0.560
6.9920
6.790
Equipment Leakage Current (Alternative method) in
mA
0.0086
0.009
0.7861
0.803
2.4880
2.500
Equipment Leakage Current (Direct method) in mA
0.0067
0.007
1.7970
1.815
9.0500
9.200
Equipment Leakage Current (Differential method)
in mA
0.0172
0.018
0.8331
0.846
4.3750
4.480
Figure 11. Medical Electrical Safety
Analyzer
Figure 12. DUT and user interface
connection points
Applied Part Leakage Current (Alternative & Direct
method) in mA
0.0095
0.010
0.1159
0.117
2.6470
2.520
Insulation Resistance ( kΩ)
49.850
51.24
273.10
276.0
2711.0
2643
XII. PHOTOS
Figure 13. System connected with a medical equipment
XIII. CONCLUSION
Figure 8. Controller PCB
Through this development an indigenous model of the
portable medical elecrtical safety analyser is made first time in
India. Internationally, only very few test equipments based on
IEC62353 standards are available. Bluetooth connectivity for
mobile applications is an added feature.
The price of the system is much less than that of imported
equivalents. This will enable hospitals in developing countries
to buy and do the routine electrical safety testing of medical
equipments, thus reducing the hazards for patients, physicians
and other clinical staff.
REFERENCES
Figure 9. Relay PCB
[1]
[2]
[3]
[4]
[5]
[6]
Figure 10. Inernal view of safety analyzer unit
View publication stats
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