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new to oscilloscope - probe questions

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willeo6709
Posts: 1
Joined: March 22nd, 2015, 7:21 am

new to oscilloscope - probe questions

Post by willeo6709 » March 22nd, 2015, 7:35 am

I have a machine tool with a flakey hi-resolution encoder on a servo spindle drive. The system consists of a high resolution twin - encoder on the actual spindle with "preamp 1" and a second high res single - on the servo drive motor going through " preamp 2". After hiring a factory service guy who can't seem to get it quite right I decided to purchase my own scope for my own shot at it. I am trying to measure amplitudes of sine wave signals of 0.8-1.0 Volts AC and I need to see a "c" mark, or index pulse in an encoder output wave. I have found no videos on doing this -.

I have a TekTronix 2445 150 mhz 4 channel analog scope. It did not come with probes, so like an idiot who can spray paint what he knows about probes on a matchbook I ordered mcmaster Carr. What showed up is AVEX 510-sw-60 ( http://www.avexelectronics.com/probes_510series.html) which says it has a bandwidth of 15/60 mhz which is lower than the scope.

Now the issue - when I try to calibrate the probes how I THINK the book says to do it I can't get the square wave to move on the front edge.... it only adjusts amplitude. Its a decent square wave with a little abberation but within limits of what I see -. so talk to me - do I need different probes? Does this thing need serviced? anybody in Iowa who can get me a crash course on my scope trying to do what I need to do?

steve_tech
Posts: 36
Joined: October 19th, 2010, 12:05 pm

Re: new to oscilloscope - probe questions

Post by steve_tech » March 24th, 2015, 2:15 pm

As you have found, there is a lot more to good scope probe design than is readily apparent. I suggest you see our ABC's of Probes for the background. The 2445 has 15 pf of input capacitance which happens to be the lower limit for the probes you have.

Make sure you are using them in 10X mode. Your rise time will be much slower than that of the scope but may work for low frequency signals. Tektronix P6134C is the recommended probe for your scope. You may be able to find some. They really do make a difference.

Make sure you learn how to use an external trigger. I think that will help based on you issue. XYZ's of Scopes talks about that.

Steve

cracked ide chip
Posts: 67
Joined: October 1st, 2015, 8:47 am

Re: new to oscilloscope - probe questions

Post by cracked ide chip » November 9th, 2015, 8:47 pm

0.8-1.0 Volts AC. that should be safe to connect to (correct ground chosen)

sounds like to me the Tek and the original probes are well more than sufficient: and return the "ordered" ones before 30 days return has passed.

what rpm does it spin at ? how many pulses per rpm are possible ?

also you say encoder but i assume it's more a decoder (your reading a signal off a "sensing apparatus" which is excited by the spindle / spinning thing). i could have it backwards though, maybe your encoding onto the spindle and cant find what was encoded.

if you have a Delay Trig sweep Pot/Knob on your scope you can do some fancy things to show a wide signal and catch part of a shorter pulse and show both. youtube has an excellent example of a Tek scope using the feature. also: a recording scope might be appropriate if you need to "research what was recorded" in several different lights.

Did you consider the reason your not seeing the "key" pulse in the wave might be:

(1) it didn't happen because it's broken, you did have the scope set right and should have seen it

(2) the "key pulse" is far smaller / shorter than the ac wave, and if you can see (several) ac waves your zoomed out way too far ?

-------------------------------
machine shop wise:

you should have an on-site replacement to prevent downtime cost if merited

you should decide the cost of studying the repair (the $ hours) and spend no longer studying it than compared to replacement costs merit, added with likely cost of repair itself. will these exceede quick replacement?

good luck

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