How bad of an idea would it be to have external switchable banana jacks for DMM? - Page 1
Forum section: electronics / beginners

author: xlzslayer
author_rank: Contributor
timestamp: March 27, 2025, 01:32:18 am
content: The idea is that you'd wear out your jacks less by having an external switch board of sorts to switch between different test probes without plugging and unplugging them. Does it make sense to implement? if so, what would be the proper way to implement this, perhaps a special type of switch is required?perhaps rigging a plastic adapter box of sorts that plugs straight into the multimeter?

author: bdunham7
author_rank: Super Contributor
timestamp: March 27, 2025, 02:42:24 am
content: Other than getting a model with a scanner card (certain Siglent and Keithley models are popular for this) I don't see how it is worth the hassle and risk unless you are switching connections many, many times.

author: pqass
author_rank: Super Contributor
timestamp: March 27, 2025, 02:58:18 am
content: I don't think wearing out jacks is a thing. They are much more robust than plugs. That's why jacks are in the expensive thing whereas plugs are on replaceable leads. Every connection (whether soldered, crimped, or just contacting) can introduce tiny voltages (thermal emf) that will affect sensitive measurements so it makes sense to minimize them.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 27, 2025, 08:20:49 am
content: Usually the wear of the jacks is not a problem.In some cases it can still make sense to have a switch instead of switching cables by hand: handling the cables with the hand will warm up the plugs and it needs some time (e.g. 20 s range) for the temperature and linked thermal EMF to settle. With a reasonable quality switch one gets less thermal issues.Switching can also be faster.If this about simple meters, I would consider getting another meter.Plugging a box directly to the meter may add mechanical force to the jacks. More likely to break the jacks from excessive force that to wear them out.

author: tooki
author_rank: Super Contributor
timestamp: March 27, 2025, 08:47:05 am
content: Quote from: xlzslayer on March 27, 2025, 01:32:18 amThe only banana jacks that “wear out” in any sense are the jacks in the very cheapest meters which are simple rolled tubes of super cheap sheet metal. In better meters, the jacks are solid metal tubes, which you aren’t going to wear out, even after decades of use. The only exceptions are the split jacks (used for input jack detection) used on many handheld meters. Those jacks are half-moons of metal in a plastic housing. But unless you abuse the jack, breaking the plastic, those also just last.Switching inputs isn’t uncommon in bench meters, as others have said. Many bench meters have switchable front/rear input jacks, and many offer scanner cards, which are really little more than banks of relays that switch a bunch of inputs (usually connected via screw terminals or a big d-sub connector), and output to banana plugs that go in the rear input jacks.For voltage and 4-wire resistance measurements, the added contact resistance these introduce is irrelevant. For thermocouple measurement, the scanner card itself usually has cold-junction compensation. IIRC, current measurements are not supported through scanner cards.Keithley’s main scanner cards have been reverse-engineered and duplicated, so it’s easy to learn how they function.Does it make sense to build a scanner card/box/device just to save wear and tear on banana jacks? Absolutely not. But if it can simplify your actual measurements/test procedures, then go for it.

author: Smokey
author_rank: Super Contributor
timestamp: March 27, 2025, 09:05:35 am
content: Quote from: tooki on March 27, 2025, 08:47:05 amhttps://www.eevblog.com/forum/circuit-studio/example-project-relay-scan-card-for-k2000-dmm/?allhttps://www.eevblog.com/forum/circuit-studio/example-project-20-channel-solid-state-scan-card-for-k2000-dmm/?allhttps://www.eevblog.com/forum/projects/diy-scanner-card-for-daq6510/?all

author: reodor
author_rank: Contributor
timestamp: March 27, 2025, 12:22:54 pm
content: The safety rating of the meter would not be valid while you're using this adapter.You'd have several sets of leads dangling off your meter at all times. If you ask me, one set is annoying enough.Just buy more meters

author: xlzslayer
author_rank: Contributor
timestamp: March 27, 2025, 03:30:22 pm
content: I see, thanks for the input guys, much appreciated. Guess it's not really worth it, as it would really just be for the sake of convenience on my part. You'd also wear out the plugs less of course, but yeh I'll just scrap the idea for now, thank you all!

author: BeBuLamar
author_rank: Super Contributor
timestamp: March 27, 2025, 04:15:31 pm
content: I have DMM's went bad but never the jacks except the jacks of one of the Fluke 87V that makes the meter thinks it has a test lead plugged into it all the time.

author: David Hess
author_rank: Super Contributor
timestamp: March 31, 2025, 02:29:27 pm
content: Old style banana jacks and plugs never fail. Newer ones which include shrouds break eventually, leaving them more dangerous when they cannot be replaced because of lack of availability and incompatibilities; every meter that I have with shrouded "safety" banana jacks and plugs uses a different version.Some multimeters have a front panel switch to select between front and back inputs.