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Forum section: electronics / beginners

author: sdouble
author_rank: Frequent Contributor
timestamp: June 21, 2014, 03:26:04 pm
content: Hi everybody,first of all i just wanted to say that i'm not a electronics fan. Electronics makes me suffer. I hated analog electronics at the university, but now, I have to play with analog parts and even design some sensitive bits. My business is to detect relativistic ions passing though detectors. i had to design very low noise charge sensitive preamps. This works relastively well. I have to power my (200) preamps with +12V -2.5V rails in a very "dirty" environment : magnets, pumps, cavities : awful electro-magnetic place. I was using simple banana connections from my bench (agilent) low voltage power supply but the noise pick up was terrible. what i'm doing now is that i use banana to bnc adapters and transmit my low voltage through a good coax (lmr195). it works muuuuch better.Now my question :is that a good practice or non-sense ?thaks for your advices.

author: SeanB
author_rank: Super Contributor
timestamp: June 21, 2014, 03:33:09 pm
content: Yes, you did find out that power supply rejection is very important. The shielded power lines are a good idea, and even better would be to use a length of twinax with the shield grounded at one end, and use the 2 cores as power rail and ground. That way you have a shielded twisted pair and better rejection of the noise.

author: sdouble
author_rank: Frequent Contributor
timestamp: June 21, 2014, 03:58:58 pm
content: I'm not accainted with twinax cabling but this shouldn't not be a big deal. Moreover it could save me some space on my pcbs. just nees to find some pcb mount connectors of that kind.

author: VK5RC
author_rank: Unknown
timestamp: June 22, 2014, 04:02:28 am
content: Looking at this post, twinax seems over priced, would two runs of coax, with the centre cables carrying the supply and return ; and the shields grounded, provide the same Isolation?

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 22, 2014, 04:14:13 am
content: Shielded twisted pair cable is used EXTENSIVELY in the audio segment of electronics and there are many kinds and sizes of connectors available for it.It would handle your rails inside a shield. You could even find 3 conductor shielded if you wanted to shield the power ground node, as well.I would think that proper shielding of the preamps, and filtering the power ingress through the shielded environment would go along with shielding the power wiring.Note that Cat5 and Cat6 cable is also available in a shielded variety, along with shielded connectors, and is dirt-cheap. We actually use Cat5 and Cat6 cable to run noise-free audio through (because the twisted-pair are SUPER-BALANCED).

author: VK5RC
author_rank: Unknown
timestamp: June 22, 2014, 10:44:58 am
content: DohShielded cat 5 much better price!

author: SeanB
author_rank: Super Contributor
timestamp: June 22, 2014, 11:38:18 am
content: If you need high current then industrial shielded control cable is cheap as well, though the connectors can be quite big and bulky.

author: theatrus
author_rank: Frequent Contributor
timestamp: June 22, 2014, 04:22:52 pm
content: Belden has a whole line of 2-wire+foil shield cable in industrial jackets designed for RS-485 communications. The wire is often beefier 20-18 gauge so can run decent currents.Provide your own connectors or use terminal blocks.