Rigol Oscilloscope Probes - Page 1
Forum section: electronics / testgear

author: leafi
author_rank: Regular Contributor
timestamp: August 05, 2013, 02:19:37 am
content: Hey everyoneI have the option to keep either the RP3300 or the RP3300A probes with my DS2072. I would like to know if you all know if the A version is better than the not A.The A version is fixed 10X where the non-A is 1X-10X switchable.The A version has 13+/-3 pF of input capacitance where as the non-A has 16 +/- 5pF.The A Bandwidth is speced at 300Mhz where as the non-A is speced at 350Mhz.The A is much thinner which will make probing that much easier but I would like to be able to measure power supply noise which a 10X probe will hinder with this scope due to the internal noise of the scope. (Using 1X you can measure the ripple cleaner even thought the BW is only 8Mhz.)The A does not spec the rise time so it is hard to compare that.The A does come with 2 different low inductance ground springs which is nice where the non A has 1. I do not have a sig gen to be able to test the probes out to 300 Mhz so I can not really get a feel for which one is better.Any opinions?Thanks

author: Unknown
author_rank: Unknown
timestamp: August 05, 2013, 09:08:50 am
content: From your description, the RP3300A just seems like a better probe. I would keep the RP3300A. I use 10x probes a lot more than 1x probes, and actually use a dedicated Tek P6101 1x probe that I got cheap for the times I want to measure ripple or something similar. You can always get a cheap 1x/10x probe, which I guess should be fine for the ~audio frequencies of a 1x probe. The effective bandwidth of a 1x probe is often lower than you would expect anyhow because of the low input impedance at MHz frequencies.

author: leafi
author_rank: Regular Contributor
timestamp: August 05, 2013, 03:56:38 pm
content: Based on Bandwidth the RP3300 are better @ 350Mhz vs the RP3300A @ 300Mhz.I think I will keep the A probes most of my other probes are 1X/10X and I hate the switch.

author: Mr Simpleton
author_rank: Unknown
timestamp: August 05, 2013, 04:01:10 pm
content: I'd say keep the A probes.If you are using a 70 MHz scope, you will not notice the 300 vs 350 MHz bandwith. But this do change a bit if you look at 200 MHz with 300 vs. 350 MHz probes.

author: Unknown
author_rank: Unknown
timestamp: August 05, 2013, 04:14:24 pm
content: I'm skeptical about the 350 MHz figure. In general switchable probes have worse performance than non-switchable probes. For example, Tek's fastest 1x/10x probe is 200 MHz, Lecroy's fastest is 300 MHz and Agilent's fastest is 350 MHz, while they all make 500 MHz fixed 10x probes. It could very well be that the RP3300 was too aggressively specified, and they fixed that in the RP3300A.

author: nctnico
author_rank: Super Contributor
timestamp: August 05, 2013, 04:17:21 pm
content: First calculate the impedance of a 1:10 probe at 200MHz and then look at how much a typical circuit can drive at such frequencies. As a rule of thumb you can't use high impedance probes to measure frequencies over 100MHz.

author: leafi
author_rank: Regular Contributor
timestamp: August 05, 2013, 05:16:50 pm
content: Quote from: nctnico on August 05, 2013, 04:17:21 pmI guess that is why things switch to active probes when they go faster. I have some 1.5GHz active probes for my TDS7404 but I do not like to turn that on because I want it to last. Plus it only has 1M sample depth :-/You all wouldnt happen to know if there is a keygen for that do you? :-)

author: signals
author_rank: Contributor
timestamp: August 05, 2013, 09:16:35 pm
content: I'd probably go for the A model just because it doesn't have the cheesy switch on the side of the probe. I just had the yellow plastic "switch" piece on the side of my RP3300 fall off the probe and into the DUT this afternoon. Was fun fishing it back out.

author: leafi
author_rank: Regular Contributor
timestamp: August 05, 2013, 10:28:14 pm
content: Thank you all for your feedback. I think I agree that the 3300 may have been over spec'ed but I do not have a way to confirm that. I have other 1X probes so Ill keep the 3300A. Thanks everyone. Now I just need a sig gen so I can test that.

author: Electro Fan
author_rank: Super Contributor
timestamp: August 05, 2013, 11:00:53 pm
content: Quote from: nctnico on August 05, 2013, 04:17:21 pmnctnico, any chance you might be up for walking us through an example of such a calculation with a brief explanation of the underlying theory/principle? Thanks, EF

author: nctnico
author_rank: Super Contributor
timestamp: August 05, 2013, 11:56:50 pm
content: Quote from: Electro Fan on August 05, 2013, 11:00:53 pmZ=1/(2pi * f * C) So a 10pf probe will have an impedance of 80 Ohms at 200MHz. Thats a long way from 10M Ohm at DC... Now imagine measuring a circuit with a meter which puts a resistor of 80 Ohms between a testpoint and ground.