Probe attenuation on Philips PM3320A - Page 1
Forum section: electronics / general

author: joelby
author_rank: Frequent Contributor
timestamp: December 14, 2009, 08:16:28 am
content: Hi all,Earlier this year I acquired a vintage Philips PM3320A DSO and got some probes and after much fiddling decided that it was a bit faulty as it wasn't able to measure DC voltages at all, and even the voltages of signals seemed suspect. I eventually decided that it was an expensive write-off and got a Rigol DS1102E after discovering this blog (maybe Dave should buy a shipping container of them and re-sell them to people here?).Anyway, I just noticed that the probes I bought for the Philips are 100x. Sure enough, using the Rigol probes at 1x I can measure DC voltages perfectly. So, does anyone know if it's possible to set attenuation on this particular Philips scope, or on similar Philips scopes? I've dug around the menus and can't see a setting, and don't have the user manual for it.Cheers, Joel

author: Unknown
author_rank: Unknown
timestamp: December 14, 2009, 08:40:11 am
content: Hi Joel,I have not seen this unit, but *most* scopes have the probe division set from the channel menu ie on a tek you push the channel button (eg CH1) then you can set the coupling (DC,AC,GND) division ratio, bandwidth limit etc.Hope this helps (I did a quick search for a manual online and came up with not much)

author: joelby
author_rank: Frequent Contributor
timestamp: December 14, 2009, 09:05:24 am
content: Thanks for your reply. Yep, that's right where I'd expected to find it too. All it has are AC, DC, GND, and a DC offset control. I've got the service manual, which mentions passive probe attenuators and says "Offset read out is changed accordingly".Actually, at the very end of the manual it mentions a Philips probe: "This 10 x attenuator probe is provided with a special BNC plug with built-in resistor for automatic range indication to advance the V/DIC reading by 10x". Sounds annoying!

author: Neilm
author_rank: Super Contributor
timestamp: December 14, 2009, 07:39:32 pm
content: I don't know that unit but I have used Philips scopes in the past. The scope probe has another connector on the BNC connector. It shorts out a ring around the BNC connector that the scope reads and automatically selects the gains. So much easier than changing a setting in a menu. It has nothing to do with wanting to tie you into using their probe...

author: joelby
author_rank: Frequent Contributor
timestamp: December 15, 2009, 12:51:53 am
content: Thanks a lot, Neilm! There is a small pin to the left of the two input BNC connectors - this must be it. I'll see if I can find out what the appropriate resistors to use are and have a fiddle.

author: qno
author_rank: Frequent Contributor
timestamp: December 15, 2009, 11:54:21 am
content: Hi Joel,I have a PM3394 and there the probe attenuation is in the UTIlities menu.You can select :1,:10 etc.There is also a scale factor. If you are using a strange divider you can scale it to any number you like.This comes in handy when measuring current by measuring the voltage over a resistor in an existing circuit.

author: joelby
author_rank: Frequent Contributor
timestamp: December 16, 2009, 02:24:55 am
content: I don't have the Setups and Utility buttons the PM3394 has, but hopefully it might mean the setting is buried in there somewhere. Thanks!