Things you must know when using an oscilloscope - Precautions for use

There are many users who are not very good at operating an oscilloscope, so in this chapter, we will learn how to set up and start using an oscilloscope, especially how to ground the oscilloscope and the user, set up oscilloscope control functions, calibrate the oscilloscope, connect the probe, and compensate the probe.

Proper grounding is an important step when setting up measurements or working with circuits. Proper grounding of the oscilloscope can prevent the user from getting an electric shock, and proper grounding of the user can prevent damage to the circuit.

Proper grounding

Grounding the oscilloscope means connecting the oscilloscope to a neutral reference point of an electrical appliance, such as grounding. Connect the oscilloscope's three-pronged power cord to a socket connected to a grounding device to achieve grounding of the oscilloscope.

Oscilloscope grounding is necessary for personal safety. If high voltage contacts an ungrounded oscilloscope chassis, any part of the chassis, including the knobs, may be insulated, and an electric shock may be delivered. When the oscilloscope is properly grounded, the current is transferred to the ground device through the ground path instead of through the user's body to the ground device. Grounding is also necessary for accurate measurements using an oscilloscope. The oscilloscope needs to share the same ground as any circuit being tested.

Some oscilloscopes do not require a separate connection to ground. These oscilloscopes have chassis control functions isolated to keep the user away from any possible shock hazard.

If you are handling integrated circuits (ICs), you also need to ground yourself. ICs have tiny conduction paths that can be damaged by static electricity built up in the user's body. Walking on a carpet or taking off a coat and then touching an IC lead can ruin an expensive IC. To combat this, wear a grounding wrist strap. A grounding wrist strap safely transfers static electricity from your body to a grounding device.

Setting control function

With the oscilloscope plugged in, take a look at the front panel. The front panel is generally divided into three main areas, labeled Vertical, Horizontal, and Trigger. Your oscilloscope may have additional areas, depending on the model and type.

Note the input connector on the oscilloscope. This is where you connect the probe. Most oscilloscopes only have two input channels, each of which can display a waveform on the screen. Multiple channels are useful for comparing waveforms. MSOs also have multiple-division digital inputs.

Calibrate Instruments

In addition to setting up the oscilloscope correctly, it is recommended to perform a regular self-calibration to make accurate measurements. Calibration is required if the ambient temperature has changed by more than 5°C (9°F) since the last self-calibration, or once a week. This can sometimes be enabled as "Signal Path Compensation" in the oscilloscope menu. Refer to the oscilloscope manual for a more detailed description.

Connecting the probe

Now you are ready to connect the probe to the oscilloscope. If the oscilloscope is properly matched, the probe can deliver the full processing power and performance of the oscilloscope, ensuring the integrity of the measured signal.

Measuring a signal requires two connections: the probe tip connection and the ground connection. The probe usually comes with a clip connection that grounds the probe to the circuit under test. In practice, the ground clip can be connected to a known ground in the circuit, such as the metal chassis of the product being repaired, and the probe tip touches the test point in the circuit.

Compensation probe

Passive attenuating voltage probes must be compensated for the oscilloscope. Before using a passive probe, you must compensate the probe so that its electrical characteristics are balanced for the specific oscilloscope.

You should make it a habit to compensate the probe every time you set up the oscilloscope. Probe adjustments can degrade measurement accuracy. Most oscilloscopes provide a square wave reference signal on a terminal on the front panel that is used to compensate the probe. The procedure for compensating the probe is usually as follows:

1. Connect the probe to a vertical channel

2. Connect the probe tip to the probe compensation signal, that is, the square wave reference signal

3. Connect the probe ground clip to the ground.

4. Observe the square wave reference signal

5. Correctly adjust the probe so that the corners of the square wave are square