buying my first Oscilloscope

[queglay]

hello this is my first post. I've been experimenting with the bedini ssg for a few months now.

I'm looking at getting a tektronix oscilloscope. I've never even used one
before but i want something that will suit all my bedini motor needs in the future,
and also for analyzing PWM signals for hydrogen generation which I don't know
too much about but I believe to be in the KHz range.

looking at the tektronix site the lowest the scopes seem to go is 40MHZ. Can
anyone please help point me in the right direction on this? thanks for any advice guys...

[morpher44]

Can
anyone please help point me in the right direction on this? thanks for any advice guys...

I too will be buying a scope soon.

I've had my eye on a USB Digital Storage Oscilloscope DSO-2090.
The bandwidth is 40mhz which isn't that great.
These come up on ebay for auction about 2 new ones per week or so.

The advantage to a storage scope & USB is you can do nice captures for presentations, etc.

Another alternative is to get a used 100Mhz scope on Ebay.
100Mhz is really what you want. Anything less is kind of slow unless you are ONLY doing audio work. Everything these days is pretty high speed. If you mess around with microcontrollers (or plan to), consider 100Mhz.
You will need 2 channels / Dual trace / at a minimum.

Lots of used scopes are being sold off as the baby-boomers retire.

[queglay]

thanks for the reply.

how come the techtronix scope only go down to 40mhz when i would want to be able to measure down to khz, or even potentially hz?

[wrtner]

hello this is my first post. I've been experimenting with the bedini ssg for a few months now.

I'm looking at getting a tektronix oscilloscope.

I think that the SSG would benefit from a relatively low quality
scope of the sort that is software, and you plug into your sound
card. Free - the software is public domain.

However, when it comes to studying the pulses given off, it is
quite another matter. They can be at least 700 - 800 volts, and
happen very sharply.

Oscilloscopes are items most people do not get right first time.
Get the software and a long cable with attenuation for your
sound card. And get a cheap s/h model from ebay to feel
your way in the field. (If you still know your old Physics teacher
from school, you might be able to take the gear in and test it
on the best scope that they have).
Paul-R

[queglay]

thanks. by s/h does that mean sample/hold?

[jibbguy]

Regarding the "40 Mhz"; that refers to the maximum Frequency you can see clearly with it without "roll off" attenuation from it's circuitry (a filter capacitor that blocks any F's higher than that from being seen).... Not the "minimum"; for that it is always all the way down to "DC" there are settings in the software that controls this device to let you choose the desired Time Base ("y-axis resolution").

I would use a separate PC "cpu box" with an old mother board for a cheapy "sound card scope"; as they have an alarming propensity for burning up, and it usually kills the entire motherboard in the process.

That "DSO-2090" appears to be fairly pretty decent USB unit (which provides some protection for the PC as the amplifier "front end" is in a separate box). The Frequency Response of "40Mhz" is not too bad for about 80% of the F-E techs i've seen so far (but more is better of course).

But please note that the "100 MHz max. sampling rate" is another figure of much importance here. It means that if you are using 2 channels at once, "50 Meg" sample rate is the fastest you can go, which may allow some very fast transients to be "Aliased" (not seen). When using only one channel at a time, you can sample at the max of "100 Meg". You need 10 samples per waveform to get any sort of accuracy when looking at signals that are not repeatable or simple Sine or Square waves... So you can say that the actual USABLE Frequency Response of that scope is: "10 MHz" for ONE CHANNEL, and "5 MHz" for TWO CHANNELS (that is assuming 10 samples per waveform to eliminate "Digital Signal Aliasing").

Another important spec is the DC Max Protected Voltage: Which is "35 Volts" (...kinda low and disappointing).

Now this can be "350 Volts" if you use a "X10 Probe" instead of the standard probe they provide (...you can buy them at the Shack)... But you must then remember that the readings on the scope are 10 times lower than stated. That "350 V DC" would be enough to look at Peak to Peak of 120VRMS wall power, but not much more. If you put a "19 Megohm" resister in line with the standard scope probe, that would then give you around "700 Volts DC" max (... In that case, the 19 megohms plus the 1 meg Ohms inherent to the device, gives a total input impedance of "20 Meg".. Then the voltage seen on the screen would have to be multiplied by "20").

This is because the standard unit has 1 Megohm of Input Impedance inside of it, and the standard "x1" Probe has no additional resistance inside of it. An optional "x10 Probe" would have a 9 Meg resistor inside to bring that total R to 10 Megohms. Many of these Probes have a switch for "x1" or "x10", which is useful but dangerous if you forget to move the switch.

One last "Spec of Interest": This thing has "8 Bit Resolution" which means there are 256 steps in the voltage reading ("x" axis). At 5 Volts full scale, that is an error of "19 mV's: (one Bit of resolution; one digital "step"). "10 Bits" is common these days and provides more accuracy, however again (... just like "Maximum Allowed Voltage", and "Maximum Sample Rate"), it raises cost.

This is a "Single Ended to Ground" device (not truly Isolated), so you must be careful where you put the "Signal Low" ground lead of the probe: It cannot be connected to a point "off ground" or bad things can happen (check the spot you wish to put the probe's ground lead with a multi-meter first, reading V between it and actual Ground). Most scopes are "Single-Ended"; the exceptions being the battery powered portable "scopemeters" like the "Fluke 199" we've been talking about (they are usually much more expensive, however). You can do without Isolation for most applications, but reading directly across Coils (which generally float off-ground) is usually a big "no-no"... They don't replace smoked input circuitry under Warranty

[queglay]

man the limitation to connect it to ground sucks. i was under the impression
that much of the bedini type stuff would require conection across the coil.

thanks alot for that very comprehensive breakdown, I've got some food for thought.

[jibbguy]

Your Welcome

I forgot to mention, that if you set a scope to "AC Coupled" that you don't even need to hook up the ground lead to read an AC signal . So you can still read across them and just leave the ground lead open, and just not see the DC component (because when "AC Coupled" it won't read any DC.. But when set to "DC Coupled" it reads both AC and DC together).

[tjnlsn255]

I have the Vellman PCSU1000 USB PC two channel scope with external trigger and I like it very much.

I got it at MB Electronics online...

Of course my local electronics surplus store had a nice used Textronics for $120 right after I purchased my Vellman PCSU1000.... oh well.....

All I can say is I really enjoy having a scope .... a picture is worth a thousand words.....

The Vellman web site has online support and downloads for their scopes also... I downloaded the software for Windows XP and it works great.....

Good luck in your search..... it is worth every penny.....

Be happy.....

Tj

[mlindeblom]

JYETech Low cost

I just bought the 062 Digital Oscilloscope from Seeed Studio | Arsenal and freelancer for interaction engineering for $33USD in DIY kit. It is not a kit for the inexperienced due to very small SMD parts. The fully assembled version is $49 USD.

It gives me a good idea of what's going on in my SSG.

It doesn't compare to the 200Mhz Tek scope, I am used to; however: it allows me to:

a) measure cap discharge timing
b) hall effect measurements
c) classic h wave views
d) build 555 circuits to spec

The best measure of rise time for a SSG is to use neon across the coil without a charge battery. Look for a white to purple flash before the parts burn up. I don't know how you measure RE other than with a gas discharge tube. This method is for test circuits only unless you have lots of money for replacement parts.

[queglay]

on the dso 2090 i see-

Voltage Range:
- 10mV ~ 5V/div @ x1 probe
- 100mV ~ 50V/div @ x10 probe
- 1V ~ 500V/div @ x100 probe
- 10V ~ 5000V/div @ x1000 probe

does that mean the max voltage i can plug into it is 10v with a x1000 or i will cause damage?

and if the max is 10V, why would it be 5000V per division on the screen?

thanks alot for the tips guys.

[FuzzyTomCat]

Hi queglay,

Here are a few Tektronix PDF's on scopes and probes you may find informative.

XYZs of Oscilloscopes

ABCs of Probes

Regards,
Glen

[queglay]

thanks for those guides, very useful.

do you guys think the dso 2090 would be able to measure those super fast transients of radiant energy at all?

[wrtner]

thanks. by s/h does that mean sample/hold?

Actually, I meant secondhand.

But sample and hold is good. I associate it with the more expensive
digital scopes.

Paul.

[Inquorate]

First Oscilloscope

Bought my first Oscilloscope on ebay, 50mhz dual trace, $300 au.

Yippee!