A place to discuss hardware/software and diagnostic procedures
VR crank sensor DC or AC coupling
3 years 3 months ago - 3 years 3 months ago #45278
by Chad
"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."
I have learned more by being wrong, than I have by being right.
Replied by Chad on topic VR crank sensor DC or AC coupling
If the signal does not ride on a Bias Voltage, it does not make a difference. The signal's amplitude will oscillate above, and below, 0 volts. However, if the signal rides on a bias voltage, as many do, the signal will oscillate above, and below, the bias voltage.
For example, let's forget about the Variable Reluctance sensor, and think about a vehicle's system battery voltage. To work with round numbers, let's say 12 Volt.
If the system voltage was fluctuating between 11 volts and 13 volts, and we plotted the voltage on a labscope, the waveform would be a 2 Volt AC sinewave, riding on 12 Volts. All the "action" is happening in a 2 volt range. However, depending on your scope, you may HAVE to have your screen on a 20 volt scale. If your scope has limited zooming capabilities, like Snap-on, this makes the 2 volt "action" very small.
In the example above, the DC is 12 volts. The AC is the 11 volt to 13 volt oscillation. There is 2 volts of AC "riding on" 12 volts of DC.
AC coupling "filters" out the DC part of a signal. In the example above, if we turn on AC coupling, the 12 volt DC will be "filtered out". The signal will now oscillate between -1 volt and +1 volt. The "action" is exactly the same but, now, we a can set our scope to a 5 volt scale and get a much bigger picture on the "action" (AC).
Going back to the Variable Reluctance Sensor. The exact same principle applies. If there is no bias voltage, AC or DC, it does not matter. The signal will oscillate above, and below, 0 volts. However, if there is a bias voltage that the signal rides on, the signal will oscillate above, and below, the bias voltage. Turning on AC coupling "filters out" the bias voltage.
For example, let's forget about the Variable Reluctance sensor, and think about a vehicle's system battery voltage. To work with round numbers, let's say 12 Volt.
If the system voltage was fluctuating between 11 volts and 13 volts, and we plotted the voltage on a labscope, the waveform would be a 2 Volt AC sinewave, riding on 12 Volts. All the "action" is happening in a 2 volt range. However, depending on your scope, you may HAVE to have your screen on a 20 volt scale. If your scope has limited zooming capabilities, like Snap-on, this makes the 2 volt "action" very small.
In the example above, the DC is 12 volts. The AC is the 11 volt to 13 volt oscillation. There is 2 volts of AC "riding on" 12 volts of DC.
AC coupling "filters" out the DC part of a signal. In the example above, if we turn on AC coupling, the 12 volt DC will be "filtered out". The signal will now oscillate between -1 volt and +1 volt. The "action" is exactly the same but, now, we a can set our scope to a 5 volt scale and get a much bigger picture on the "action" (AC).
Going back to the Variable Reluctance Sensor. The exact same principle applies. If there is no bias voltage, AC or DC, it does not matter. The signal will oscillate above, and below, 0 volts. However, if there is a bias voltage that the signal rides on, the signal will oscillate above, and below, the bias voltage. Turning on AC coupling "filters out" the bias voltage.
"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."
I have learned more by being wrong, than I have by being right.
Last edit: 3 years 3 months ago by Chad.
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