Rigol Probe query...Oscilliscope newb. - Page 1
Forum section: electronics / beginners

author: necroscope
author_rank: Regular Contributor
timestamp: October 15, 2012, 03:05:52 am
content: Just recieved my new Rigol DS1102E and have got it all set up and calibrated the probe and ready to troublshoot a few PCB's,The question i have is the aligator clip on the ground for the probe is too big to latch onto the ground pin of most TTL ic's,Can you buy a different ground clip to suit the rigol probe and are all the aftermarket probes made with the same connectors ect and if i were to run an extention to the main ground on the pcb would this interfere with the calibration of the probe,Please forgive my simple questions but this is my first scope and the first time i have used one.thanks.

author: w2aew
author_rank: Super Contributor
timestamp: October 15, 2012, 03:34:00 am
content: I'm not sure about the availability of different ground leads for the Rigol probes. In all cases though, you really want the ground lead to be as short as practically possible. The importance of this goes up as the frequency of your signals goes up (or as your risetime gets shorter). For best signal integrity in the scope, use the shortest ground lead possible. Extra ground lead length adds inductance the ground path resulting in ringing and distortion of high speed signals - not to mention how increasing the loop area between the probe tip and ground will increase the amount of noise the probe will pick up.In the short term, if you can't find a suitable ground lead and clip, solder a short length of bus wire to the ground pin of your ICs (if possible) and attach the clip to that. You can unsolder it when you're done. For high speed circuits, wrap your temporary ground wire around the coaxial ground shield adjacent to the probe tip to minimize the ground lead length and loop area.

author: necroscope
author_rank: Regular Contributor
timestamp: October 15, 2012, 03:50:57 am
content: Thank you for the advice,extending the ground is out of the question then,How would it affect the probes performance if i were to remove the alligator clip and solder on a mini grabber or similar product like in the following link?http://www.display3000.com/shop_english/electronics/logic-analyzer/grabber-small-and-professional-for-logic-analyzer.html

author: LoyalServant
author_rank: Regular Contributor
timestamp: October 15, 2012, 04:32:10 am
content: You can buy minigrabber ground leads for scope probes.Now.... you can change the group clip and not hurt anything.I buy sets of el cheapo $30 probes to modify when I have the need to do something unique.My take on that is not to modify the original set of probes hence buying the throwaway probes.You just got your scope.. it's probably best you not alter the leads just yet.Just my two cents.

author: necroscope
author_rank: Regular Contributor
timestamp: October 15, 2012, 04:47:53 am
content: Quote from: LoyalServant on October 15, 2012, 04:32:10 amThanks mate,I will get some el cheapo's to modify,Do you have a link to anywhere that sells the minigrabber ground leads for scope probes? or do they have a certain name or brand google is just throwing up Q9 aligator clips it is like looking for a needle in a haystack.

author: LoyalServant
author_rank: Regular Contributor
timestamp: October 15, 2012, 05:25:49 am
content: I was actually trying to remember where I got them.I think it was at a hamfest some 15 years ago so I know that's not much help.They were an original part for a LeCroy scope if I remember correctly.Ebay and amazon turned up nothing...Surprised these buggers are hard to find and I know I have seen them in a catalog.I tossed all my Digi Key catalogs out in favor of the online version..... probably should have kept one!

author: PA4TIM
author_rank: Super Contributor
timestamp: October 15, 2012, 06:32:57 am
content: You can cut off the clip and solder a new one to it, i had to do it on both Rigol probes within a few months. The wires were broken inside. One probe more or less still works after 3 year ( but they are terrible) the other died within a few months. So buying cheap probes for 30 dollar and alter those is not a good idea, they are probably better ( and more expensive) as the original probes.Keep the ground leads as short as possible escpecially on squarewaves to avoid over/ underschoot and ringing. Your scope is 50MHz so you can see squarewaves upto 5 MHz in every detail, And 10MHz for a estimation of what is goinig on. So above that you probably have no problem, the overshoot and ringing will not be visible any more and digital signal will start to look as sinewaves.http://www.pa4tim.nl/?p=3059there are some pictures of Rigol probes with and without groundleads and also a compare with other probes. My Rigols were 100 MHz versions ( from my DS1102A that i have sold again because I reky started to hate the #%^} thing.

author: necroscope
author_rank: Regular Contributor
timestamp: October 15, 2012, 08:58:26 am
content: Thanks for the advice PA4TIM,you know when you compare the rigol probes to the $8 free shipping from china ones on ebay they pretty well look identical,I dont think i will lose any sleep refitting a grabber clip after all you cant get much more Dodgey bros than an aligator clip anyways.I dont fully understand what i am doing yet but i think i was seeing that ringing buisness today on some ic's usually when i wen to the next ic using the earth pin of the ic before it,once i had the alligator clip wedged in i didnt really want to disturb it,it certainly makes a big difference to see whats going on rather than using my trusty logic probe and datasheets/schematics(if available) I still cant tell the difference between a faulty output and a good one but at least i can see some activity happening instead of just a high/low led on a probe.. :-)