oscilloscope not certain if I shorted it. - Page 1
Forum section: electronics / beginners

author: golash
author_rank: Contributor
timestamp: February 12, 2015, 01:24:20 am
content: HiThis is the second day for this total beginner in oscilloscope usage. Today I was attempting to tunemy diy 3 axis cnc servo motors. Before I made any connections to the servo driver. I had a trace when theoscilloscope was powered up. I was also able to see a square wave when I did the probe adjust.So I made the connections to the servos drivers and powered up the machine. Since the time of the testingof the servos. Now it seems I cannot get a trace or even a square wave. I`m wondering if I shortedout the oscilloscope or changed so many settings that the wave form is hidden. It seems I`m in over myhead.Thanks

author: miguelvp
author_rank: Super Contributor
timestamp: February 12, 2015, 04:55:24 am
content: What is the scope model, that would help.Also if it has a test signal, hook your probe to it and press the Auto button if it has one.Or if it has self-calibration, take off all the probes and do a self cal.Again, if you let us know the brand/model it will help also pictures can be helpful.

author: golash
author_rank: Contributor
timestamp: February 12, 2015, 10:49:17 am
content: HiThe model is a tektronix 442

author: Andy Watson
author_rank: Super Contributor
timestamp: February 12, 2015, 11:09:22 am
content: Do you see anything if you press the Beam Find ?

author: golash
author_rank: Contributor
timestamp: February 12, 2015, 11:25:00 am
content: HiNo reply from the Beam Find

author: janaf
author_rank: Frequent Contributor
timestamp: February 12, 2015, 12:06:18 pm
content: Shorting the inputs does not damage anything. Just abut the only thing that can damage inputs is if there are "very high" voltages applied to inputs. What "Very high" is depends on scope model and probe/probe setting.Have you tested both channels?

author: golash
author_rank: Contributor
timestamp: February 12, 2015, 12:22:20 pm
content: HiHere is the only observation i can make. No idea if it tells us anything. If I hold down thepower button. I see a horizontal trace for the period of time the power button is depressed.Removing finger from power button shows no trace

author: tiltit
author_rank: Regular Contributor
timestamp: February 12, 2015, 03:45:11 pm
content: May I ask where you connected the scope's ground lead? I'm asking that because I once connected a scope probe across an H-bridge and shorted it out due to the common ground.

author: Andy Watson
author_rank: Super Contributor
timestamp: February 12, 2015, 06:08:47 pm
content: Quote from: golash on February 12, 2015, 11:25:00 amIf the beam finder does not show anything there may be a fault with the scope. How did you obtain it? Do you know its history?

author: golash
author_rank: Contributor
timestamp: February 12, 2015, 07:06:01 pm
content: The ground lead was connected to a ground. I had instructions for the placement of the probes.Of course I could have made a mistake even with instructionsIts a ebay purchase some years ago. I took a chance.I`m now thinking that I should purchase a new scope. It is going to be used at the moment totune my servo drives. But I am also into violin making and an oscilloscope is used to help tunea violin plate. I`d prefer not to pay more than $300. Some of the frequencies are in the rangeof 440 hertz for violin tuning. Would a $300 scope handle that spec.

author: katzohki
author_rank: Frequent Contributor
timestamp: February 12, 2015, 07:13:43 pm
content: Yeah, you can get a decent enough scope for $300 price range. Rigols are popular for a little bit more. If you're looking at used I think $300 would get you something fairly good, but older.

author: golash
author_rank: Contributor
timestamp: February 12, 2015, 08:25:30 pm
content: Would this be a good choice: Siglent SDS1072CML price 319

author: katzohki
author_rank: Frequent Contributor
timestamp: February 12, 2015, 08:31:54 pm
content: I don't know much about Siglent personally, but looks ok. If you could afford $400 the Rigol DS1054Z would probably be VERY good value for your money.

author: janaf
author_rank: Frequent Contributor
timestamp: February 12, 2015, 09:11:16 pm
content: One thing about the original problem. Anything with inductance; coils, motor, electro-magnets etc, can cause high voltage spikes when turned off. If your motor drivers are of a switched type, they may be the cause.Second, the probes usually have setting slike 1x, 10x, x100 with 10X is the most common. The X is actually a divider, ie a 10x probe divides the signal by ten, and if you set the scope input to X10 it will multiply the result by ten to get the right reading. When working with inductors, coils, set the probe to 10x or better 100x until you have seen what the signal looks like. That will give some protection to your scope from high peaks.PS You can see an inductor and causing an inertia for elecricity. Trough ann inductor, Current is "hard to start, hard to stop", has inertia. A traditional car ignition coil is simply a magnetic coil that you run current through. When you cut the current, it has "nowhere to go" but converts into a high voltage spike. In cars, this converts 12V to short ignition spike of several thousand volts.

author: golash
author_rank: Contributor
timestamp: February 12, 2015, 09:40:16 pm
content: Hi JanafVery good information. I`ll apply that info to the next scope.

author: albert22
author_rank: Regular Contributor
timestamp: February 12, 2015, 10:43:33 pm
content: Quote from: golash on February 12, 2015, 12:22:20 pmForgive me if this sounds silly. But did you check that the power switch of the oscilloscope is working ok?. This is obvious if the scope has a power on led. If not. Try to turn graticule illumination fully on and use it as a power on indicator. The power supply of the 442 surely it is based on a transformer you can check for continuity to see if the switch works properly.Good luck

author: Yago
author_rank: Frequent Contributor
timestamp: February 13, 2015, 12:27:38 am
content: Quote from: golash on February 12, 2015, 12:22:20 pmNot an expert on these, but that power button sounds dodgy.