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| Would this work as an AC probe? |
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| vk6zgo:
--- Quote from: Hero999 on October 16, 2018, 03:39:28 pm --- --- Quote from: Beamin on October 16, 2018, 02:26:00 pm ---I thought about connecting the probe directly to the hot lead being mindful not to let the ground clip near anything but I thought for good practice in order to not pick up noise you used the ground lead. Therefore negating the results of my test. I should have asked this first: The current path through a scope is not high impedance like through a multimeter? When the scope is on 50 ohm setting is it like a 50 ohm resistor or like 50 ohm feedline? what is the scope at when not in the 50ohm setting? So hooking scope probe directly to hot and neutral, or inadvertently your ESD mats ground and the hot side of a power supply you are probing is like creating a dead short? --- End quote --- On all settings the oscilloscope's 0V at the same potential as mains earth. With the oscilloscope in the high impedance setting, it's possible to probe the phase conductor, with the ground clip disconnected, as long as the probe and oscilloscope both have the appropriate CAT rating. When the oscilloscope's input is set to 50Ohm, then its imped impedance is 50Ohms which is useful because a length of 50Ohms co-axial cable can be connected to its input, giving an input impedance of 50Ohms, up to a certain frequency beyond that of most instruments --- End quote --- The most common use for the 50ohm setting on a 'scope (where provided) is so you can look at the output of devices which have a 50ohm output impedance. This can be a device under test (DUT) the signal source, or a monitor point provided on a device with a different output impedance. Built in 50ohm terminations were not particularly common in the past, as a lot of Oscilloscopes were used with systems where the standard impedance was not 50ohm. For instance, analog video, where the standard impedance was 75ohm. In most cases, the 'scope as supplied had a 1Megohm input impedance, & external terminations were used. --- Quote --- It enables a low-Z probe to be made from a length of 50R co-axial cable and a 450R resistor, giving a total input impedance of 500R. This may seem like a lower impedance, than a standard x10 probe, with a DC impedance of 10M, but it has less capacitance and a higher impedance, above a few tens of MHz. The 50R termination resistor will only have a low power rating of a couple of Watts at most and will be damaged if it's connected to too higher voltage. --- End quote --- For this reason, leave your 'scope in the high impedance mode when messing with possible high energy sources. |
| Beamin:
Scope is a tek 2465 That I'm still learning... |
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