Test circuit for a withstand voltage tester

Details Test circuit for a withstand voltage tester Test circuit for a withstand voltage tester

1999-10-19

2003-04-15

Huynh, Kim (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

With specific voltage responsive fault sensor

C361S042000

Reexamination Certificate

active

06549385

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a withstand voltage tester, and more specifically to a test circuit for a withstand voltage tester, which has a safety means to keep the operator from the risk of suffering a sustained electric shock.
When electric appliances are manufactured, they must be examined through a series of safety compliance tests before delivery. The withstand voltage test is a compulsory production test on electric appliances. The test voltage for such a withstand voltage test can be as high as 5,000V. Because an operator may have to test a large number of electric appliances within a short length of time, an accidental contact of the hand with the test circuit may happen, thereby causing an accidental electric shock.
FIG. 1
shows a test circuit
1
for a withstand voltage tester according to the prior art. The test circuit
1
comprises a high voltage source
11
. The high voltage source
11
is connected to a current detection device
15
through an electric line
13
. The current detection device
15
is connected to the test sample (electric appliance to be tested)
17
through an electric line
13
. The current detection device
15
is also connected to a withstand voltage tester (not shown), which is in turn connected to the high voltage source
11
. The test circuit
1
is also connected to the grounding terminal
18
through the electric line
13
. When the body
2
touches the test circuit
1
accidentally, electric current passing through the current detection device
15
is equal to the value of the electric current A
1
passing through the test sample
17
plus the value of the electric current A
2
passing through the human body
2
. If A
1
=10 mA, A
2
=80 mA, and the preset trip current of the withstand voltage tester is 100 mA, the total current A=A
1
+A
2
=90 mA<100 mA. Therefore, the tester does not trip off, and the high voltage source
11
keeps outputting the high voltage A. Under this condition, the operator may subject to the risk of continuous electric shock by a high voltage.
FIG. 2
shows a test circuit
1
for another structure of withstand voltage tester according to the prior art. This test circuit
1
comprises a high voltage source
11
. The high voltage source
11
is connected to a current detection device
15
′ through an electric line
13
. The current detection device
15
′ is connected to the test sample
17
through an electric line
13
. The current detection device
15
′ is also connected to a withstand voltage tester (not shown), which is in turn is connected to the high voltage source
11
. The test circuit
1
is connected to the grounding terminal
18
through an electric line
13
. Normally, the electric current A
1
which passes through the test sample
17
is detected by the current detection device
15
′. However, when the human body
2
touches the test, circuit
1
, the current A
1
passing through the human body
2
is not detected by the current detection device
15
′, i.e. the current detection device
15
′ detects only the current A
1
passing through the test sample
17
. Therefore, the high voltage source
11
keeps outputting the high voltage current A, and the operator may subject to the risk of a continuous electric shock by a high voltage.
As indicated above, the aforesaid prior art test circuits cannot keep the operator out of the risk of suffering a sustained electric shock. If the operator touches the test circuit
1
accidentally during a test, the high voltage current A
2
passes through the grounding terminal
18
to the operator's body, causing the operator to be injured by the electric shock. The warning word of “Danger! High Voltage!” on the withstand voltage tester does not help to keep the operator from an electric shock.
SUMMARY OF THE INVENTION
The present invention has been accomplished to provide a withstand voltage tester which eliminates the aforesaid problem. According to the present invention, a second current detection device is installed in the test circuit and connected to the high voltage source and the overload-protective current detection device. The second current detection device comprises a switch connected to the high voltage source, and detector means connected to the ground to detect a high voltage. When the human body touches the test circuit and receives a high voltage through the ground, the detector means detects the presence of the high voltage, and outputs a signal to the switch upon such a detection, causing the switch to cut off the circuit between the high voltage source and the test sample.


REFERENCES:
patent: 3555360 (1971-01-01), Lee
patent: 4087846 (1978-05-01), Hughes et al.
patent: 4313085 (1982-01-01), Balchunas
patent: 5481194 (1996-01-01), Schantz et al.
patent: 5675465 (1997-10-01), Tanaka et al.
patent: 5939993 (1999-08-01), Burtin et al.
patent: 5963405 (1999-10-01), Engel
patent: 6278596 (2001-08-01), Simpson

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