Automotive Oscilloscope Settings and Precautions

① When testing the ignition high-voltage line, a dedicated capacitance probe must be used, and the oscilloscope probe cannot be directly connected to the ignition secondary circuit.

   ②When using a car oscilloscope, be careful to keep it away from heat sources, such as exhaust pipes, catalysts, etc. Excessive temperature will damage the instrument.

   ③When testing with an automotive oscilloscope, pay attention to keeping the test line away from rotating parts such as fan blades and belts as much as possible.

   ④ During the test, confirm that the hydraulic support of the engine hood is in good condition to prevent injury to the head or damage to the vehicle oscilloscope when the engine hood automatically descends.

   ⑤ During the road test, do not place the car oscilloscope on top of the dashboard. It is best to hold it in your hand for testing.

   2. Signal frequency and time base selection

   The purpose of the time base/frequency table is to help select the time base or determine the frequency of the displayed waveform based on the signal frequency.

   How to use the time base/frequency table: You can use an automotive oscilloscope to determine the signal frequency by counting the number of cycles (1-5) of the waveform displayed on the screen. The first column on the left side of the table is the determined frequency number, and the other columns are the current time base numbers.

   3. Oscilloscope settings essentials

   When using an oscilloscope to test an unknown signal, how to set up the oscilloscope is a rather complicated matter. This section explains the basic method of setting up the oscilloscope when using an automotive oscilloscope to capture waveforms. It can help readers understand and master the essentials of oscilloscope settings.

   The time base setting value is determined according to the signal frequency.

Table 1 Time base frequency conversion table

   1) Set up the project

   In order to display a waveform, the oscilloscope must be set as follows:

   ① Voltage ratio;

   ②Time base;

   ③Trigger level (you can also set the trigger mode to "automatic");

   ④Coupling mode (AC, DC or GND).

   a. Direct current (DC) coupling mode.

   b. AC coupling mode: This mode can filter the DC part of the signal and only display the AC component. It is often used to observe the waveform of two-wire variable magnetic negative magnetoelectric sensor signals, as well as the noise in the signal and the generator ripple voltage (diode) or other less common examples.

   c. Grounding GND mode: This mode is used to determine the grounding position or 0V voltage level or to display the 0V voltage reference point of the oscilloscope.

   2) Setting instructions

   ① When the displayed waveform can be clearly seen using the automatic setting function (AUTORANGE), you can use the manual setting (MANUAL) to further fine-tune it.

   ② If the waveform is still not clear on the display, you can make assumptions about the voltage ratio and trigger level based on your inferences and not set the time base for now.

   ③ Use a digital multimeter to measure the signal voltage and set the voltage range ratio according to the measured voltage.

   ④ Set the trigger level to more than half of the signal voltage. After setting the voltage ratio and trigger level, the only thing left unset is the time base.

   ⑤At this time, manually set the time base. Most signals should be between 1 millisecond and 1 second.

   ⑥ The time base/frequency table can be used to help select the time base. You can first use the cursor on the car oscilloscope to measure the signal frequency, then determine the number of cycles (number) of the desired displayed waveform, and then find the intersection of the signal frequency and the number of cycles (number) from the table. This is to determine the time base.

   3) When the waveform cannot be captured

   ①Confirm that the trigger mode is in "AUTO" mode. If it is in "AUTO" mode, the car oscilloscope may not trigger.

   ②Confirm that the screen display of the car oscilloscope is not in the frozen (HOLD) state. If the screen is frozen, press the release button.

   ③ To confirm whether the signal really exists, you can use a multimeter to check the voltage first. If you are sure that the signal exists, but cannot be captured by the car oscilloscope and multimeter, check the connection between the test wire and the terminal.

   ④Confirm that the coupling mode is not in the "GND" mode. If it is in the "GND" mode, no signal can enter.

   ⑤Confirm that the trigger source is defined on the selected channel.

   4. Oscilloscope terminology

   Trigger level: the starting voltage value when the oscilloscope displays;

   Trigger source: trigger channel of the oscilloscope [channel (CH1), channel (CH2) and external trigger channel (EXT)];

   Trigger edge: the rising or falling edge of the waveform displayed by the oscilloscope;

   Voltage ratio: the voltage value represented by each vertical height;

   Time base: the time value represented by each horizontal length of the grid;

   DC coupling: measure AC and DC signals;

   AC coupling: only allows the AC component of the signal to pass through it, filtering out the DC component (capacitors are used to filter DC voltage);

   Ground coupling: confirm the 0V voltage position displayed by the oscilloscope;

   Automatic triggering: If there is no manual setting, the oscilloscope will automatically trigger and display the signal waveform.