Oscilloscope

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ShowMaster
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Oscilloscope

Post by ShowMaster » Thu Sep 05, 2013 2:54 am

My JDR 2000 scope has developed hum in the baseline. My 4ch tec scope (1987) scope has triggering issues.
So.. I'm thinking if a new digital one. I think I want a desktop scope not PC based. My $ range is $400.
The Rigol DS1102E 100 MHz 2-Channel Digital Oscilloscope
Seems to be a favorite. I could use any user input on it or others.
I plan to repair the JDR but it's still dated. The tec scope the same if I get to it. I'm tired of old test equipment.
No new planes for awhile of I do buy it. It's tough having a tech hobby and a rc hobby at the same time.

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rperkins
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Re: Oscilloscope

Post by rperkins » Thu Sep 05, 2013 3:20 am

I have the rigol ds1102E . It works well for me after I got used to it. I'm not an advanced enough user to recognize or be constrained by its limitations. I know there was a hack to get the 50mhz model up to 100 mhz, but at the time I was purchasing the price point wasnt very much so I just bought the 100mhz version.
I bought from saelig.
http://www.saelig.com/MFR00068/PSPC017.htm

I still have my old tektronix 2225 scope but dont use it anymore. I bought that one used because it is what I was familiar with years back. I hisses when first powering up ( HV power supply ?) but settles down in a minute or 2.

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ShowMaster
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Re: Oscilloscope

Post by ShowMaster » Thu Sep 05, 2013 7:01 am

I think my tec scope is a 2224. I'll have to check. In any case it's got sync loss issues.
About the Rigol scope,
Do you get schematics with it and is there a service manual? What about FW support?
I like the small footprint and other features.

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cre8tiveleo
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Re: Oscilloscope

Post by cre8tiveleo » Thu Sep 05, 2013 12:15 pm

rperkins wrote:I have the rigol ds1102E . ...
Too funny, I just bought this model last month, same place too, I LOve iT!

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rperkins
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Re: Oscilloscope

Post by rperkins » Thu Sep 05, 2013 12:27 pm

I notice he's still offering a free case too. I usually unsubscribe from newsletters but have been reading his.

Showmaster, i havent seen any firmware, schematics or service manuals except the 3rd party reverse engineering stuff. Havent really looked all that hard though.


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Kilrah
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Re: Oscilloscope

Post by Kilrah » Thu Sep 05, 2013 1:00 pm

The days where design docs were supplied with devices are looong gone... at least for "cheap" devices, maybe if you get a $20k scope from HP you'll have them...

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ShowMaster
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Re: Oscilloscope

Post by ShowMaster » Thu Sep 05, 2013 1:58 pm

Ok thanks everyone.

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ShowMaster
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Re: Oscilloscope

Post by ShowMaster » Thu Sep 05, 2013 3:21 pm

Ok, ordered! I guess my free field repairs fee just went up.
The local hobby shop kid gets $5 a solder connection. I'll do it for $2.50 or 3 for $5 now.

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Re: Oscilloscope

Post by jhsa » Thu Sep 05, 2013 6:53 pm

:mrgreen:
My er9x/Ersky9x/eepskye Video Tutorials
https://www.youtube.com/playlist?list=PL5uJhoD7sAKidZmkhMpYpp_qcuIqJXhb9

Donate to Er9x/Ersky9x:
https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=YHX43JR3J7XGW

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rperkins
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Re: Oscilloscope

Post by rperkins » Thu Sep 05, 2013 8:50 pm

congrats. It took a little while to get used to it but all is good now. I like how It will measure the freq and amplitude and you dont have to count the lines on the graticule . I usually keep the bandwidth limit on, and the memory set to 'long'( well I thought i did) just went to check and neither one was set, but I had just used the 'auto' button. It did a good job setting up the trigger for a ppm signal, but maybe it changed those settings ?? I know nothing except the fact of my ingorance :) ( I said that to one of my coworkers every day when he asked me ' how I was doing') He quit asking :)

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ShowMaster
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Re: Oscilloscope

Post by ShowMaster » Thu Sep 05, 2013 9:10 pm

It'll be fine. Like all tools it may not be used every day but it'll be great when I do. I just got tired of so so older scopes I collected over the years. My bench top will be so empty now.
I was going to try FPV or a Quad this year but decided that I can buy that stuff at any time and at bargain prices. Not so with the scope. So scope first.
I liked the utube videos on the scope operation I watched.

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rperkins
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Re: Oscilloscope

Post by rperkins » Fri Sep 13, 2013 11:07 pm

Have you had a chance to use it yet ? Just curious how it is working out ?

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ShowMaster
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Re: Oscilloscope

Post by ShowMaster » Sat Sep 14, 2013 1:56 am

I used it today to work on a friends 2 rds8000 radios. I needed to see what pins on the trainer plug were ppm out. 2 is ground and 3 is ppm out on the 5 pin dins labeling.
I did measure the ppm as 8v ptp positive pulses and I think I read the vertical correctly.
I also opened up the radio and probing I found a good place on the board to monitor the ppm into the Ed stage. I wanted to see both the master and trainer PPMs when switched to compare their waveforms. We thought there was a difference between the 2 radios. They both are ok and it was a Dilantin trim on the trainer that wasn't set. He swore he was trimming it but now I know he couldn't have been, the radios are working fine
I wasn't expecting that level.
Now to come up with a 5v ptp square wave generator I can use as a known voltage reference.
It seems to do it all and sure freed up bench space.
I did try the auto measurement function, pretty nice.
I did try a 8.25 battery as measured with my $50 DVM and the scope read 9.02 volts as I remember. I'm just seeing what it does. I printed out the manual and like opentx, er9x, I've got another OS to learn.
Get ready for questions and answers in the new forum topic I may start.
So the scopes already in service one day out of the box.

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rperkins
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Re: Oscilloscope

Post by rperkins » Sat Sep 14, 2013 2:03 am

cool. Looks like it was right on time.

It does have a reference signal in the lower right. Cant remember what it is.
It does take time to learn to get around. Like everything else today with 'soft function' buttons, a lot of the features are buried in the menu system.

I wont be a lot of help but will be watching for your comments/questions

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ShowMaster
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Re: Oscilloscope

Post by ShowMaster » Sat Sep 14, 2013 11:41 pm

I remembered that I bought 2 MHz crystal Osc for unbricking 9X m64's. one was a spare.
I mounted one on a perf board along with a lm7805 regulator. I'm running it all on a 9v battery.
It came out great and can now be used as a scope reference as well. The 1102 on auto reports 5.03 area ptp and 1 MHz.
There are some leading ant trailing overshoots that using the 20 MHz mode cuts way down.
I could use some ideas on making the edges and overshoots cleaner as well as a more precision 5v supply.
I'm thinking that if I fed the pulses into a transistor that gets saturated and cutoff it could make it cleaner. Then just a better 5v source.
Not important just playing with the scope and unused parts I have.
The 1102 calibrator is rated at around 3v ptp but not recommended as a reference, just for adjusting 10x probe modes.
The auto measure mode is really nice.

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rperkins
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Re: Oscilloscope

Post by rperkins » Sat Sep 14, 2013 11:55 pm

Ok that makes sense about the calibration signal output .

I'd had mine a couple months before I realized there was a calibrate feature on the scope. Somewhere ( the manual ?) I read to let the thing warm up for at least 20 minutes before running the calibration routine. It didnt take real long but more than 2 minutes I think. I dont know if it made a difference or not.

Another feature that I missed at first was that you can push in the knob on the horizontal axis to 'zoom' in on the waveform. I like that also.

I have not used my old techtronix scope since I got the new one. Maybe I oughta get rid of it ?

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ShowMaster
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Oscilloscope

Post by ShowMaster » Sun Sep 15, 2013 2:55 am

My Tek scope is failing and I just don't have the interest to repair it.
I'm afraid it's doomed.
I'll miss having all the option knobs on the front instead of a menu but that's progress.
So far I really like the Rigol.

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ShowMaster
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Oscilloscope

Post by ShowMaster » Fri Sep 20, 2013 7:01 am

A question for Tandy or others with the Rigol 1102 or similar scope.

I wanted to look at the total ppm out on my Taranis and er9x tx. I had trouble setting the trigger and the data train display kept jumping. I read up on it and decided to try the delayed trigger option.
I set the trigger for descending leading edge. When I got to 12ms delay setting the trace became stable on the screen and I could see all the channels.
Is this the correct way to use the trigger delay and it 12ms a normal value to use? Seems to work ok so I'll stay with it for now.
I'm just trying out all the scopes features.

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Kilrah
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Re: Oscilloscope

Post by Kilrah » Fri Sep 20, 2013 8:35 am

Not sure about the Rigol, but my Hantek has a "pulse" trigger feature (high or low pulse, narrower than... or wider than...).
This is perfect for PPM as you just trigger on "low pulse wider than 3ms" for a positive PPM, it syncs on the idle pulse and stays rock stable whatever you do.

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rperkins
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Re: Oscilloscope

Post by rperkins » Fri Sep 20, 2013 9:33 am

I've experimented with the delay ( holdofff ?) and the pulse trigger as Kilrah mentions. Probably used the pulse option more than the delay. Sometimes I forget to switch the trigger from ch 1 to ch 2. The 'auto' button sometimes gets me a stable pules when I cant get it right.

I bought a broken music mixer to fix. The problem is the switch mode power supply. When troubleshooting with the scope I tripped the mains breaker several times. Watched a Davee Jones eevblog video to figure out why. Looked at how much an isolation probe costs. Considered an isolation transformer. Then worked around it exactly how they say not to :( . Was wondering if I powered the scope from a computer UPS if it would remove the earth ground. Maybe if I didnt plug the ups into the mains ?

Anyway waiting on parts now as I ruined the common mode choke on the mains input . I've never investigated a SMPS so been reading up on them. In my case no blown fuses , components, or diodes that read bad. Thinking maybe it is in the feedback circuit. It uses an opto isolator

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Kilrah
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Re: Oscilloscope

Post by Kilrah » Fri Sep 20, 2013 9:51 am

That's where I like my battery-powered portable Hantek scope :D

But if you do something to isolate your scope from ground and continue working from that just be mega careful as any metal part of your scope will be at potentially lethal potentials.

Best is to use 2 probes in differential mode to measure waveforms across components.

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Re: Oscilloscope

Post by SkyNorth » Fri Sep 20, 2013 1:29 pm

The Isolation transformer is the way to go , no reference. to earth ground , the output is floating
Depending on the UPS design , the output is not isolated from ground .
Breaking the ground connection on the UPS , could allow for a floating voltage differential on the outside metal case due to current leakage.
touching the case and a real ground point could prove lethal, as Kilrah pointed out.

You can use a "cheater plug" , that removes the ground connection from the scope ,But unless you are 100% confident in your setup , you risk serious
personal injury, if you make a mistake.
Remember in North America , The Neutral and Ground wire are theoretically the same point , and both can carry current back to the source.

I have also had problems floating a scope , in that RF can cause strange readings on the scope , as the scope case is now part of the input channel.

IF the UPS was unplugged , and you are running off a battery , then you should be OK , though there may still be noise pickup issues .

-Brent

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rperkins
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Re: Oscilloscope

Post by rperkins » Fri Sep 20, 2013 2:15 pm

Kilrah wrote: Best is to use 2 probes in differential mode to measure waveforms across components.
Thanks. I'll have to look into this
SkyNorth wrote: The Isolation transformer is the way to go , no reference. to earth ground
....
the output is floating Depending on the UPS design , the output is not isolated from ground .
...
You can use a "cheater plug" ,
...
I have also had problems floating a scope , in that RF can cause strange readings on the scope , as the scope case is now part of the input channel.
Thanks for the reply.

I used the 'cheater plug' but was tellng myself not to do it. I think an isolation xformer or 2 identical xformers wired back to back is within my budget. I'd have to drag my ups out of service on my server to use it. It'll run my server for about 10 minutes (400 watt ps or so) so I think it could run the scope for awhile

Just like usual you spend almost as much on parts and tools to repair over replace. But you gain knowledge, tools and the extra contingent parts you overbought due to shipping considerations

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Re: Oscilloscope

Post by SkyNorth » Fri Sep 20, 2013 2:27 pm

To use two probes , keep them referenced to circuit ground , and measure both sides of the part in question ,one probe on each side.
Use the scopes "subtract" function, to subtract the lower probe from the upper probe , and this will give you the reading across the part
in question.
This keeps the scope grounded , and is the safer way to measure things.

-Brent

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Re: Oscilloscope

Post by ReSt » Fri Sep 20, 2013 2:38 pm

I found some good informations on how to troubleshoot Switched Mode Powersupplies on this site
http://www.kellerstudio.de/repairfaq/sam/smpsfaq.htm

Reinhard

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ShowMaster
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Re: Oscilloscope

Post by ShowMaster » Fri Sep 20, 2013 2:42 pm

The Rigol is rated at 50 watts. How about using two 120 to 240 travel converters back to back? Must be the transformer type and many are under $20 each.
I'm going to also check out my local surplus parts house for some transformers to maybe make my own isolation transformer.
I also have a 100 and a 400 watt modified sine wave inverter to try. The 100 watt one maybe would run ok on a lipo pack.
Just brainstorming in case I ever need a isolated power source but I guess this could also make the scope really portable. There's room in the scope bag for it all if the 100w inverter would work. It's palm size.
I'll give it a try and see what noise or other issues are created. At 50 watts I think it would draw around .5-.6 amps at 12v to make 120v at 60 watts, assuming 100% efficiency. 100% is not posable so under an amp at 12v is still a reality on a 3 cell lipo pack.
I like fuzzy math because its never wrong, I just keep changing values to make it correct.
Feel free to add your own values.

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rperkins
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Re: Oscilloscope

Post by rperkins » Fri Sep 20, 2013 5:39 pm

Cheaper than ruining my scope

http://www.ebay.com/itm/321143753473

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Re: Oscilloscope

Post by SkyNorth » Fri Sep 20, 2013 6:00 pm

The "Travel converters" are not isolated.

Most voltage converters that use a transformer , use a Auto Transformer.
This type of transformer has only one winding , with different voltage taps available. NO ISOLATION at all.

To provide true Isolation , you need two windings separated by proper electrical insulation

You could use Two 120Vac to 24VAC transformers ...you would hook the two 24V windings together,
this would provide 120V in and 120 Vout But each transformer will have to be double the working wattage you need
So Two 100watt transformers at best could deliver 50watts best case.

Line Isolation transformers usually are big and heavy and $$$
http://www.hammondmfg.com/pdf/5c0069.pdf
Check out Digikey # 169QS-ND

These look nice as well ...complete package.
http://www.ebay.com/itm/Dale-Fluke-IT40 ... 3753473%26

-Brent

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rperkins
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Re: Oscilloscope

Post by rperkins » Fri Sep 20, 2013 10:52 pm

SkyNorth wrote: You could use Two 120Vac to 24VAC transformers ...you would hook the two 24V windings together,
this would provide 120V in and 120 Vout But each transformer will have to be double the working wattage you need
So Two 100watt transformers at best could deliver 50watts best case.-Brent

I cant figure this part out. I thought xformers were very efficient and the way a xformer manipulates the E and I does not change the P=EI ratio . Where is all this lost power going ? Are the xformers going to dissipating 4x as much heat by coupling them back to back ? I can see how the xformer loss would be additive if you used more than one of them , but cant see past that point.
thanks for shedding some light on this for me

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Re: Oscilloscope

Post by SkyNorth » Sat Sep 21, 2013 1:10 pm

Transformers suffer core losses due to eddy currents , and hysteresis. , this is why they slice up the core and laminate each slice , and then laminate all the pieces together , to form one core.
The main loss in a xfmr is the (I x I x R) read as "I" "squared" "R" losses. This is the internal resistance of the wire,

When connecting the two secondary windings together , one is the source , the other is the load. Each has its own internal resistance.
To achieve "Maximum power transfer" the "source" resistance must match the "load" resistance. When this happens you get a voltage divider,
with equal voltage drops across each. , this means the power transfer is split evenly between the two. This is where most of the the heat comes from in a xfmr.

So to summarize - Maximum power transfer is 50% , when load matches the source resistance. the losses increase when they are not matched.

-Brent

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