Biomedical Engineering Reference
In-Depth Information
Patient
(applied part)
A
(medical)
B
(Non-medical)
Signals
Signals
?
PE
PE
Figure 4.1-33 A non-electromedical device (B) within the patient environment. Source: From IEC-60601-1 (2005).
The insulation level is also specified. It is defined both
in kV, creepage distances and air clearances in millime-
ters. Important additional specifications are related to
maximum exposed surface temperature, protection
against water penetration (drop/splash proof), cleaning-
disinfection-sterilization procedures, technical and users
documentation.
A non-medical device such as a PC may be situated
within a patient environment (instrument B in
Fig. 4.1-
33
), but in itself it must not have an applied part. An
electromedical device (instrument A) must be inserted
between the B and the patient. The connection between
A and B is via the signal input/output of device A. If the
instrument B has higher earth leakage current than 500
m
A, an insulation power line transformer or extra ground
must be provided. The reason for this is that a person can
transfer the enclosure leakage current by touching the
enclosure of B and the patient simultaneously. During the
single fault condition of a broken ground wire to B,
the earth leakage current of B may then be transferred to
the patient. This would not happen with the inter-
connected signal ground wires as shown in
Fig. 4.1-33
,
but could happen if A and B were in the same rack with
one common power cord.
An electromedical device may have more than one
applied part (
Fig. 4.1-34
).
Signals
B, BF
or CF
Functional earth
Power line
PE
CF
Figure 4.1-34 Electromedical equipment with two applied parts.
The producer must basically declare the intended use
of his equipment. If an applied part is intended to be used
in direct connection with the heart, it must be of type CF.
The same instrument may have another applied part
intended to be used with skin surface electrodes or sen-
sors. That applied part may be of type B, BF or CF. A plug
in the instrument may be marked with type B, but a box
with a galvanic separation may be inserted in the cable so
that the applied part is converted from type B to BFor CF.
