If you intend to connect the oscilloscope to a circuit that is connected to the supply voltage, you must use an isolation transformer. But the oscilloscope shouldn’t be floated by the isolation transformer. The device under test should be floated.
Isolation transformers are used to separate two circuits. The isolation of power eliminates transients and harmonics from the supply power and ensures safety. The ratio of primary and secondary voltages of an isolation transformer is 1:1.
Oscilloscope Isolation Transformer
An oscilloscope test is done to visualize the variation of voltage over time. The signals are plotted on a graph. If the circuit under test is connected to the main supply lines, the test becomes dangerous as high-frequency noise from the power source is added to the circuit under test.
To suppress the high-frequency noise, you must add the isolation transformer between the main supply and the circuit under test. An oscilloscope is a ground-referenced device. Connecting your oscilloscope to the isolation transformer nullifies the ground connection and results in floating your device.
Oscilloscope Test
To test a circuit with an oscilloscope, you must connect the ground connector of the scope’s test lead to the ground of your circuit and then attach the probe to the point in the circuit where you want to test. Oscilloscopes are made ground-referenced because of safety purposes.
The BNC cables of the oscilloscope are already grounded internally. Hence, even if you don’t attach its ground connector to the ground of the circuit, the connection will work absolutely fine. But your measurements will be more accurate if your circuit under test and your oscilloscope have the same ground.
What Will Happen if You Connect the Oscilloscope to an Isolation Transformer
The voltages of the primary and secondary sides of the isolation transformer are the same. If you connect your oscilloscope’s probe with the isolation transformer, the probe of your oscilloscope will gain the voltage of the primary side of your isolation transformer. So, your oscilloscope will be floated.
Floating your oscilloscope is very risky and you won’t get accurate results either.
What is the Purpose of the Isolating Transformer in the Oscilloscope Experiment
An isolation transformer in the oscilloscope experiment ensures safety and suppresses high-frequency noise and direct current noise. These are present in the main power supply line. So, if you connect your oscilloscope to a circuit that is to be connected to the main power supply line, you must use an isolation transformer.
A transformer is used to increase or decrease the voltage. But an isolation transformer doesn’t serve this purpose. It breaks a circuit into primary and secondary so that direct current noise can’t get through.
How Do You Isolate an Oscilloscope
You can isolate your oscilloscope by isolating your circuit under test. If you connect an isolation transformer between the main power supply and the circuit to be tested, you will be able to establish a connection between the main supply and the circuit to be tested by magnetism. But there isn’t any link to earth.
As there isn’t any direct contact between the main power supply and the circuit to be tested, there won’t be any high-frequency noises added from the main power supply line.
Do I Really Need an Isolation Transformer
Isolation transformers are needed for safety purposes and accurate output of oscilloscope. Isolation transformers have two coils- primary and secondary. The primary coil converts the incoming electrical voltage to a magnetic one and thus induces an electric field in the secondary coil.
Hence a voltage appears at the output that is the same as the input voltage without any direct link between them. The lack of direct connection between the main supply and the circuit to be tested suppresses the high-frequency noises from the main power supply line.
When Would You Use an Isolating Transformer
You have to use an isolating transformer for ensuring safety and to remove unwanted signals. These two things are related to where very high voltage like the main power supply is present.
For Safety
You will need an isolating transformer when you have to work with the main power supply. The lines that are provided to our houses from the main supply run through an isolating transformer also. This is to ensure safety.
The main power supply line may have high-frequency noises. The high-frequency noise and direct flow current can pass to the circuit when connected directly. This can be hazardous. So, an isolation transformer is a must in such cases.
Reducing electrical noises
As isolating transformers are coils, inductance is related to it. Inductance is a barrier to high-frequency signals. So, the use of an isolation transformer can block the passing of electrical noises.
Frequently Asked Questions
Can an oscilloscope measure mains voltage?
An oscilloscope can measure main voltages but it’s very dangerous. Any measuring device is dangerous to use in the main power lines as the supply voltage is very deadly. So, you must work with caution.
Conclusion
The use of an isolation transformer while working with high voltages is necessary. It ensures the isolation between your circuit to be tested and the power line. While using an oscilloscope in such cases, you mustn’t float your oscilloscope as it would be dangerous. Rather you must float the device or the circuit that you are testing.
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