Difference between AC/DC
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From: Timmins,Ontario,Canada
Difference between AC/DC
I know dc runs off battery, alternator produces ac power. When you test voltage at sensors i know it receives voltage from the pcm but is this in the form of ac or dc? Just wondering which current setting to use for the multimeter. I know dc travels from a high point of voltage potential to a low point, and alternating currents change direction, right?
Hotshot
Joined: Jan 2004
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From: St Louis
The alternator includes a rectifier assembly. This device, made from diodes, changes the AC produced by the alternator windings to a pulsating DC. The output is applied to the battery which acts as a filter, accepting and storing charge as needed, and smoothing the voltage out.
This DC power, called Vbatt or B+, depending on the age of the factory documentation.
All sensors that require a supply voltage use DC voltage as a supply. Most sensors ouput a DC voltage. Some output an AC voltage of varying frequency or amplitude.
In most cases, set the meter to DC volts (unless instructed otherwise) and the 20 VDC scale. Connect the (-) lead to ground and probe the circuit with the (+) lead.
Steve
This DC power, called Vbatt or B+, depending on the age of the factory documentation.
All sensors that require a supply voltage use DC voltage as a supply. Most sensors ouput a DC voltage. Some output an AC voltage of varying frequency or amplitude.
In most cases, set the meter to DC volts (unless instructed otherwise) and the 20 VDC scale. Connect the (-) lead to ground and probe the circuit with the (+) lead.
Steve
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From: Virginia
99% of the time you use the DC scale like Steve said. There are also some oddball things when you use the AC scale, and sometimes if you are working on an 80's vehicle, you need a meter that measures dwell, for pulsating DC measurement.
Always try to use a good quality digital meter when measuring stuff on a fuel injected vehicle. Any meter actually uses some of the current from the circuit you are measuring to give a reading. This introduces a slight error in the reading. The cheap meters use a lot of the circuit current, which can actually kill the circuit and give no reading at all.
Always try to use a good quality digital meter when measuring stuff on a fuel injected vehicle. Any meter actually uses some of the current from the circuit you are measuring to give a reading. This introduces a slight error in the reading. The cheap meters use a lot of the circuit current, which can actually kill the circuit and give no reading at all.
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