Duncan,
I don't see anything wrong with paralleling 2 to 4 capacitors to get close
to the exact value.
A lot of leakage current measurements have been performed using homemade
test circuits.
There are a couple of factors to be aware of. As long as the measured
current is well below
limits, the accuracy of the components should not be an issue. Most agencies
will accept
your results if you can prove that you know what the measurement error is.
You do this by
simulating leakage using a resistor whose exact value has been precisely
measured.
The capacitors in this circuit have very little effect on readings at 50 and
60 Hz. The human
body model circuit has generally not been required to be used when the
supply frequency
is less than 400 Hz.
Scott Lacey
-----Original Message-----
From: [email protected]
[SMTP:[email protected]]
Sent: Wednesday, November 24, 1999 10:42 AM
To: [email protected]
Subject: EN60950 Earth Leakage Measurement Circuit.
Group,
I am trying to construct a simple earth leakage test circuit as
in Annex D
of EN60950. I am finding it impossible to find a capacitor for Cs
(0.22uF) as I
cannot find one that is the required value, tolerence and voltage
rating.
Am I missing somthing here? Even if I use a network of capacitors I
would have
to use quite a few of them to get the right value! It would appear
that the 1%
tolerence that is requested is a bit unrealistic given the value and
required
voltage rating.
Has anybody else found this and if so how was it resolved? Are there
any
manufacturers of earth leakage testers who may be able to hint on
how they
manage to overcome this?
Any suggestions would be greatly recieved...
thanks,
Duncan.
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