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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I need a scope with four channels. I need to be able to measure the voltage difference between channel 1 and 2, and channel 3 and 4. My current scope can only has the ADD and INVERT for channel 1 & 2. Any recommendations? Capturing a triggered signal would be nice, too.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Let the voltage on channels 1 and 2 be v1 and v2. Invert channel 2 to get -v2. Add channels 1 + (inverted 2) to get v1 + (-v2) = v1-v2. Et viola, vive la difference.
To fix the "4 channel" part of the specification, you may need google and some $$
Registered Member #347
Joined: Sat Mar 25 2006, 08:26AM
Location: Vancouver, Canada
Posts: 106
We'll need to know a little more to make suggestions.
What's your budget? New or used? Analog or digital? Bandwidth requirements? Memory depth? (digital only)
I don't know of any portable analog scopes that can do two separate math channels like you describe, possibly some large mainframe scopes with the proper plug-in modules could do it. The cheapest way to do this may be two 2-channel analog scopes.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Yes, I know how to use the add and invert. I need these features for both 1/2 and 3/4.
In answer to Dr. Slack, I am willing to pay some $ to get a new scope, as mine will not do this. I would like to get used to save some money; I don't care if it is analog or digital, although digital would probably allow me to save images off of a triggered response.
Any suggestions? The guy selling this one said he thought it could
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I have a Tektronix 7603, a 75MHz analog scope with two dual trace vertical amp plugins, each of which has Add and Invert buttons. So it could display two traces at once, one being 1-2, the other being 3-4.
I paid about $180 for it used. Very used, it belonged to the Ministry Of Defence and looked like it had been run over by a tank. Having said that, it worked fine and still does.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Also worth noting is that the diferential probe will give you much better results than the add/invert maths, as it will have much better common mode rejection and the likes.
But if you would rather be able to use the extra channels individually, you will need a fancier scope the the tds2104, I have used one before and I can confirm that it had only one math function (which could be used for 1-2 2-1 3-4 4-3 1+2 3+4 or fft) I am not sure which scope can handle that, and I think it is somewhat rare (even if it is only a simple firmware issue) but I can say I have only seen it on the high speed scopes we have in our lab (talking 5 figures before you even start buying input cards!)
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Oscilloscope Recommendation
