Oscilloscope

SnowT · Guru

Oscilloscope

brian · Guru

Many Oscilloscopes cannot directly handle 240v input on their test leads, this is especially true of the type that interface to your computer via the USB port. You need to know the input voltage specifications before you try to test as you may just let the smoke out.

If it can't handle that voltage then you need to setup a series resistor bridge to be able to pick off a suitable lower voltage for testing.

You need to use resistors for this, rather than an inductive type circuit in order to keep the power factor and phase relationship clean.

Next problem is that some early CROs had one side of the test input connected to earth rather than the later fully floating method, so you need to be careful, as getting it wrong will again let the smoke out.

Next problem is that you need to use test probes with the correct signal attenuation in order to contain the vertical scale to a readable value.

Testing these voltages can be fraught with danger, so be very aware of the risks involved, you can't see it coming.

Hope this helps.

Cloak · Guru

Ok from memory.

Sounds like you are game and have some experience right. A standard oscilloscope has a very high input impedance by that I mean unlike a digital multimeter it doesn't have a current
setting. This means it is going to be very unlikely to blow anything up with it. That said just make sure by some weird fluke yours doesn't have a low impedance input before you go on.

Stick the probe in the socket you want to measure and the range on AC and timebase on something like 20 mSec for 50Hz I reckon. Just tune the dials till you can see a clear scope.

Make sure you trigger off the same input and use AC coupling. Also keep in mind that some probes have an inbuilt X10 attenuation.

You can adjust the trigger point along the signal and expand the scope using the timebase to stretch the picture so you can have a good look at cleanliness etc.

A pure sine wave might be hard to get out of most generating equipment so expect some distortion or miss shaped sine curves. Look for square edges and spikes
both of these can upset things and both are undesirable. Also once you have a stable scope picture flick input coupling over to DC and make sure the image doesn't move too
much off the centreline up or down. If it does then the signal has a DC bias which can also be a problem if it's excessive.

Hope this helps.

PeterD · Guru

SnowT wrote:
I have been given an Oscilloscope,

With such brief information there I'm wondering if I am doing the right thing offering any suggestion. What is the make and model" What is the input, BNC connector or banana plug/screw terminals?

You may be able to use one of these.

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