TR41.7.1-06-05-005-M-TAG108(Arli06-MT2-Boksiner)

archivistshipΗλεκτρονική - Συσκευές

7 Οκτ 2013 (πριν από 3 χρόνια και 8 μήνες)

88 εμφανίσεις

TAG108(Arli06
-
MT2
-
Boksiner)

May 2006

archivistship_862e01df
-
fd29
-
4df4
-
bf9c
-
da25b1aadfd1.doc


Page
1

of
7

T


AGENDA ITEM []

Proposal to amend IEC 60950
-
21, Clause 6.2.3 and Clause 6.2.1

Clause
6.2.3, Limits with one conductor earthed

Clause 6.2.1 Limits under normal operating conditions

______________________________

Impact
:

Proposal provide a more
thorough test procedure as present requirement is
not sufficient to limit current to values below 10 mA.

Background:

Clause 6.2.3,
Limits with one conductor earthed
, of IEC 60950
-
21 states:


for
RFT
-
V CIRCUITS
whose open circuit voltage exceeds 140 V d.c.
under normal operating
conditions, the current between the other conductor and earth, measured through a 2 000

2 % resistor, under any external load condition, shall not exceed the relevant line
-
to
-
earth limit given in Figure 1. Moreover, this current
shall not exceed 10 mA d.c. after 10 s.

The intent of this requirement was to limit the current available from an RFT
-
V power source
exceeding 140 V d.c to earth to 10 mA. However, the present requirement that consists of a
measurement at a single value o
f test resistance is not sufficient to assure conformance with this
current limitation for non
-
linear source.


Also, the limitation to 10 mA for power source exceeding 140 V should also apply limits under normal
operating conditions since a person might t
ouch the source under normal conditions. Finally, Figure 1


Maximum current after a single fault

is used as the limit curve in 6.2.3. This figure should not be
used in 6.2.3 as it is not consistent with
10

mA

long
-
term limit.


Rationale:

The present tex
t in clause 6.2.3 was intended to
limit the current available from an RFT
-
V power
source exceeding 140 V d.c to earth to 10 mA
. Figure 1 shows the desired characteristics of an RFT
-
V
circuit.

TAG108(Arli06
-
MT2
-
Boksiner)

May 2006

archivistship_862e01df
-
fd29
-
4df4
-
bf9c
-
da25b1aadfd1.doc


Page
2

of
7


Figure 1


䑥獩敤⁶o汴慧a
-
捵牲敮e⁣桡 慣t敲楳瑩捳iof⁒ T
-
V⁣ 捵楴
w⹲⹴⸠.慲th)

Consider a general measurement circuit for the determination of the circuit voltage
-
current
characteristics. Figure 2 shows a measurement circuit using a variable test resistor.


Figure 2


M敡獵牥浥mt⁣ 捵楴⁴o⁤整敲浩m攠eo汴慧a
-
捵牲敮e⁣桡 慣t敲楳瑩捳iof⁒ T
-
V⁣ 捵楴
w楴h 攠潵tput⁥ th敤e

Suppose the RFT
-
V circuit under test has an open
-
circuit voltage greater than 140 V. The current
flowing from the circuit will increase a
s the test resistor is decreased in value inversely proportional to
the resistor value. However, as the current reaches 10 mA, the monitoring and control device required
by clause 6.2.1 should activate to limit the current. For an open
-
circuit voltage of

200 V, the highest
voltage allowed for RFT
-
V circuit, the device should activate at 20 k


or the current would continue to
increase beyond 10 mA. Figure 3 shows the behavior of the output current as a function of test
resistance for a circuit that limits the output current to 10 mA at an open
-
circuit voltage of 200 V d.c.

TAG108(Arli06
-
MT2
-
Boksiner)

May 2006

archivistship_862e01df
-
fd29
-
4df4
-
bf9c
-
da25b1aadfd1.doc


Page
3

of
7


Figure 3


Lo慤
楮攠io⁣ 捵楴⁴h慴業楴猠瑨攠eu敮e⁴o‱  ⁡琠慮p敮
-
捩c捵楴⁶o汴慧攠潦′ 〠
V⁤⹣

Clause 6.2.3 requires a single measurement at a test resistance value of 2 k

. This means that for test

resistance values greater than 2 k


the characteristics of th
e monitoring and control device are not
verified so that the device may not provide the desired current limiting. At an open
-
circuit voltage of
200 V, test value of 2 k


corresponds to a current of 100 mA. Thus, it is possible that an RFT
-
V may
comply wi
th IEC 60950
-
21 but allow up to 100 mA current without limitation. Figure 4 shows the load
lines circuits that provide current limiting at 2 and 20 k

. Figure 5 compares the characteristics of
circuits that provide true 10 mA current
-
limiting and potenti
al characteristics of circuits that are tested
at a single value of 2 k


.

TAG108(Arli06
-
MT2
-
Boksiner)

May 2006

archivistship_862e01df
-
fd29
-
4df4
-
bf9c
-
da25b1aadfd1.doc


Page
4

of
7


Figure 4


Lo慤楮攠ao⁡ 捩c捵楴⁴h慴業楴猠瑨攠eu敮e⁴o‱  ⁡湤⁣ 捵楴⁴h慴⁣a浰汩l猠s楴h
捡汵獥‶⸲.㌠3t⁡渠 p敮
-
捩c捵楴⁶o汴慧攠潦′ 〠0⁤⹣


F楧i攠e†


䍯浰慲楳潮

of⁤敳楲敤⁶o汴慧a
-
捵牲敮e⁣桡 慣t敲楳瑩捳iof⁒ T
-
V⁣ 捵楴⁡湤†
po獳楢汥⁣桡i慣t敲楳瑩捳iof⁒ T
-
V⁣ 捵楴⁴敳t猠st′ k


on汹
w⹲⹴⸠.慲th)


TAG108(Arli06
-
MT2
-
Boksiner)

May 2006

archivistship_862e01df
-
fd29
-
4df4
-
bf9c
-
da25b1aadfd1.doc


Page
5

of
7

There is no rationale for using 2 k


as the only test resistance. Clause A.5.2 states that f
or
measurements from

one hand to both feet (between one conductor and earth), the conventional value
of 2 000

has been used. This value may represent a severe case for a linear source, but it does not
necessarily represent a severe case for a non
-
linear source such as RFT
-
V circuit with monitoring and
control device. the test resistance is intended to represent the resistance of a human body in contact
with the source and any other resistance external to equipment that limits the touch current. Typical
body resistance is u
p to 2 k


for large area of contact and up to 10 k


for a small area of contact.
Furthermore, other impedances, such as shoes or line resistance, may occur in the circuit. For a
typical telecommunication application for these types of circuits, a resistance signi
ficantly greater than
2 k


is likely and should be considered.

Based on these considerations, it is necessary to verify performance of RFT
-
V circuits over a range of
test resistances. Several test resistance between 2 and 20
k


should be used. Ione clas
s of RFT
-
V
circuits used in North American is designed to limit the current to 5 mA, so a test at 40 k


should also
be performed.

Also, clause 6.2.3 references Figure 1 of 60950
-
21 for current limits for durations less than 10 s.
However, this figure cor
responds to a long
-
term current limit of 25 mA. This figure does not
correspond to a limit of 10 mA. It is necessary to scale the figure to correspond to a long
-
term limit of
10 mA. A new figure addressing limits for RFT
-
V circuits is needed.

Finally,

clause 6.2.3 requires a measurement of the current with the other output earthed, but does not
require a measurement with the other output open
-
circuited or connected as in service. In reality, a
person may contact one output with the other output open
-
c
ircuited or in service or earthed.


TAG108(Arli06
-
MT2
-
Boksiner)

May 2006

archivistship_862e01df
-
fd29
-
4df4
-
bf9c
-
da25b1aadfd1.doc


Page
6

of
7

Proposal:

Modify

the second dash of Section 6.2.3 as follows:



for RFT
-
V CIRCUITS whose open circuit voltage exceeds 140 V d.c. under normal operating
conditions, the current between the other conductor and earth, meas
ured through 2 000

,

5 000

10 000


20 000


and 40 000


± 2 % resistors, under any external load
condition, shall not exceed the relevant line
-
to
-
earth limit given in
Figure 1

Figure

XXX
.
Moreover, the currents

measured through these resistors
shall not exceed 10 m
A d.c. after
10

s.


Figure XXX


M慸業i洠捵敮e⁴o⁥ th⁦o⁒ T
-
V⁣ 捵楴


TAG108(Arli06
-
MT2
-
Boksiner)

May 2006

archivistship_862e01df
-
fd29
-
4df4
-
bf9c
-
da25b1aadfd1.doc


Page
7

of
7

Modify

the second bullet of second dash of Section 6.2.1 as follows:



200 V d.c., provided that a monitoring and control device is used that limits

the current to
earth to 10 mA

d.c.for duration longer than 10 ms or in accordance with Figure XXX for
duration less than 10 ms
and
in case of one output grounded externally to the EUT

in
accordance with 6.2.3;

…………………………

………………………….

Compliance is checked by inspection and measurement
.

Compliance with current line
-
to
-
earth current
limitation are measured through 2 000

,
5 000

10 000


20 000


and 40

000


± 2 % resistors.