Scope Cal - Page 1
Forum section: electronics / beginners

author: Ranger14
author_rank: Regular Contributor
timestamp: February 08, 2016, 07:49:15 pm
content: I am doing some work on a scope .. I want to check cal and performance of the scope . The right tools are the best option but is it possible to check the cal with dmm and function generator ??Or could I build something to check the scope withI don't have another scope to use but would like some input or thoughts..

author: tggzzz
author_rank: Super Contributor
timestamp: February 08, 2016, 07:58:46 pm
content: The scope is only half the instrument. The other half is the probe, or whatever you use to connect to the unit under test. Especially at higher frequencies, you calibrate the combination.Beyond that, define what you want to calibrate and to what level, and compare that with the scopes specifications.Then you can compare your signal sources to what you are trying to do.

author: Ranger14
author_rank: Regular Contributor
timestamp: February 08, 2016, 08:02:51 pm
content: A couple of the input resistors are shot or out of spec and need to be replaced ... The main purpose to make sure the scope ia not way out of cal and still usable for taken measurments ..

author: tggzzz
author_rank: Super Contributor
timestamp: February 08, 2016, 09:07:45 pm
content: So, define what you want to calibrate and to what level of accuracy. Without that we are likely to give you unhelpful (albeit correct) guidance.

author: Blackwarrior
author_rank: Unknown
timestamp: February 08, 2016, 09:21:33 pm
content: I must agree with tgg, I work for a calibration company in the NE England, we calibrate everything from dmm's to complex PAT testers, scales, you name it. We have calibration equipment that costs tens of thousands of pounds, all UKAS approved.It depends on whether you use your scope for hobby or professional purposes. If hobbiist, and your function gen and DMM is more accurate than your scopes spec then you can use those, if professional, then it should go to an approved calibration company.As tgg mentioned frequency, you need to test at low and high frequencies. Dave has lots of videos on YT on oscilloscopes, watch them, fantastic info, you can't get better.

author: Ranger14
author_rank: Regular Contributor
timestamp: February 08, 2016, 10:40:18 pm
content: This scope will used for noob hobbist and I am really just learning electronics...

author: Blackwarrior
author_rank: Unknown
timestamp: February 08, 2016, 10:56:20 pm
content: It may help us if you can give the models of each, scope, function generator and DMM..I think Even for the hobbiist you still need some accuracy with your kit. So let us know what you have and help won't be far away..

author: tggzzz
author_rank: Super Contributor
timestamp: February 08, 2016, 11:52:02 pm
content: Quote from: Ranger14 on February 08, 2016, 10:40:18 pmOK, let's try this another way.What makes you think the scope is out of calibration? What makes you think your other equipment (DMM, sig gen) is more accurately calibrated?BTW, since you are workingona scope rather thanwitha scope, you should be very very careful you understand where the dangerous (1-15kV) internal voltages are.And before you use a scope, you should read and understand the safety-related references inhttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/They might reduce the possibility of a loud noise followed by deathly quiet.

author: Ranger14
author_rank: Regular Contributor
timestamp: February 09, 2016, 04:57:12 pm
content: Quote from: tggzzz on February 08, 2016, 11:52:02 pmI not sure about my function gen but I have a 5v ref for my dmm .. The scope's caps are discharged and the unit is safe to work on ..I am not sure if the scope is out cal and how would I check if I don't have the tools to cal the unit ?? The unit has several resistor that need to be replaced on the channel 1&2 which would change cal if replaced cause they are 5%tol right ??Quote from: Blackwarrior on February 08, 2016, 10:56:20 pmThe scope is a Tek 2215 with current limited supplyToolAscel AE20125 function generatorFluke 87 Series IIFluke 775V ref .01%tol 3ppmWas looking to find a 50mhz or similar..

author: tggzzz
author_rank: Super Contributor
timestamp: February 09, 2016, 10:43:57 pm
content: Quote from: Ranger14 on February 09, 2016, 04:57:12 pmI presume you are completely familiar with the consequences of HV capacitor dielectric absorbtion, a.k.a. "soakage".

author: Ranger14
author_rank: Regular Contributor
timestamp: February 10, 2016, 01:33:15 am
content: Quote from: tggzzz on February 09, 2016, 10:43:57 pmLook I know your trying to help with being safe while working on scopes ..Please help me with the issues not scope safety..

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 10, 2016, 04:04:17 am
content: Replace the resistors with the correct (BOM specified) values. Then let's see if it needs to be calibrated or not.You will read in the Tek Service Manual about necessary equipment like Time Mark Generators and Voltage Standards and all the rest. Nowadays, _for all practical purposes_ you can get by with a good DDS FG (used as pulse generator in place of the Time Mark Generator) and your highly accurate Fluke 87 DMM to cross-check voltages.I'll bet a cheezburger that you will not _need_ to recalibrate the scope after you've replaced the bad resistors. (Assuming that is all that is wrong with it in the first place.)If you need to make precise quantitative readings for some reason, this scope is the wrong instrument anyway.