Can you identify this scope probe? - Page 1
Forum section: electronics / beginners

author: dalpets
author_rank: Contributor
timestamp: June 17, 2014, 03:54:50 pm
content: I just received a second hand Trio analog 35Mhz oscilloscope (circa 1980) . It came with a HP? probe.Hand engraved on the probe is GP88100 250Mhz 20pF.It also has a slide switch with three settings viz.,"|:|, ref, I0:1".Could you tell me what the first two settings are & when to use them. It also has an inset calibration screw. Do you know how I would calibrate with that?I have no documentation on the probe & I am new to scopes.Thanks

author: cs.dk
author_rank: Unknown
timestamp: June 17, 2014, 05:16:19 pm
content: 1:1 is a "direct connection", in that sense that if you probe 1V you will read 1V on the scope - Your imput-inpedance will still be in effect though, so it's not just a wire!. Ref is often connecting the probe-tip to ground, what to use it for, i never managed to figure out.10:1 is a voltage-divider/attenuator, Probe 1V and you will read 100mV on the scope-screen.The compensation is used to get a right square-wave from the embedded signal-generator - It shoult be on front of the scope. See more her:Google for a manual for the scope - Many of these older scopes have very well written manuals. If it's a manual from a Hameg, Tek, what ever is not that important, as many of them shows and tells the "basic" usage. Only special-features needs the right manual.I've got an Aaron 20 MHz scope, and a Tek 2246 - Besides from the scope features, the how-to's are practically the same.What model is your Trio-scope?Have a look at Dave's and Allan's video's - They are quite good to tell how to do some basics (and more advanced of course)1X vs. 10X probes:Please don't forget the scope training class here - It is really good:https://www.eevblog.com/forum/beginners/oscilloscope-training-class-%28long%29/

author: w2aew
author_rank: Super Contributor
timestamp: June 17, 2014, 05:21:57 pm
content: cs.dk has got the description correct. For more information about 1x and 10x probes (1:1 and 10:1), please check out my video...

author: cs.dk
author_rank: Unknown
timestamp: June 17, 2014, 05:26:33 pm
content: Just because my limited knowledge - What is the point with the ref-setting on the probe?

author: w2aew
author_rank: Super Contributor
timestamp: June 17, 2014, 05:35:48 pm
content: Quote from: cs.dk on June 17, 2014, 05:26:33 pmIt gives you a quick way to connect the probe to ground so that you can see where the "ground" level is on the scope. With today's digital scope, this is usually indicated clearly on the screen. However, on the analog scopes, there is no on-screen indication of where ground is. So, by hitting the "ref" button, you momentarily connect the probe to ground, then you can adjust the vertical position control on the scope to move the "ground" level to a convenient spot on the screen.Also useful when you have multiple probe connected, and need to figure out which one is which on screen (again, useful on the old analog scopes where every trace is the same green/blue color).

author: dalpets
author_rank: Contributor
timestamp: June 18, 2014, 02:49:22 am
content: Quote from: cs.dk on June 17, 2014, 05:16:19 pmIt's a CS 1577A. It came with a comprehensive manual. Only had it for one day at this stage. Still fumbling around, though. I'm getting some somewhat offbeat traces & so I think, as a complete newcomer, I may need to come to terms with a DIY calibration of the CRO and/or probe.Are there more modern probes that I could use with this CRO that may be more adaptable/useful ?I presume that more sophisticated modern probes can be calibrated, as well as the CRO.I have two new CE certified 40mhz probes from China with 1x,10x, but no pF value. How would I establish the pF value for them? Am I over playing the importance of being able to calibrate probes?Thanks for your contributions.

author: w2aew
author_rank: Super Contributor
timestamp: June 18, 2014, 03:13:38 am
content: The video above will answer your questions about the probes. Basically, if you can successfully adjust the compensation on the them with your scope, then they'll like work fine for you.If you're serious about learning how to use a scope, then take the time to watch some of Dave's videos or mine. The "scopes for dopes" video that is in the sticky thread in thus forum will certainly set you we'll on your way.