Rigol - leaders in electrical safety - DM3068 - Page 1
Forum section: electronics / testgear

author: try
author_rank: Regular Contributor
timestamp: January 17, 2016, 09:46:38 am
content: Hi folks,there is someone currently offering a Rigol DM3068 on Ebay Germany.He uploaded a couple of pictures. One of them contains the manual and some spare fuses.Have a look at the fuses!They are so cute!http://www.ebay.de/itm/RIGOL-DM3068-Digitales-Tischmultimeter-6-1-2-Stellen-neuwertig-/141879082745?hash=item2108a6fef9:g:3F4AAOSwoydWmml~As far as I remember Dave never took one apart.Now you know why.RegardstryDisclaimer: I am not the seller. I am not affiliated with the seller and this thread is definitively no promotion!

author: ataradov
author_rank: Super Contributor
timestamp: January 17, 2016, 09:59:37 am
content: What's wrong with the fuses? Seem like pretty standard fuses to me.

author: ketil b
author_rank: Regular Contributor
timestamp: January 17, 2016, 10:14:46 am
content: They look similar as the ones in all my Keithley meters.

author: Gyro
author_rank: Super Contributor
timestamp: January 17, 2016, 10:22:48 am
content: I think the OP's point is that the fuses ARE pretty standard (ie. glass 20mm). However I note from the picture that the meter is only rater CAT I 1000V and CAT II 300V so it is unsuitable for use on high energy circuits.

author: EEVblog
author_rank: Unknown
timestamp: January 17, 2016, 10:23:01 am
content: Are they mains fuses perhaps?Poor form if they are the current fuses.Although bench meters usually are as highly rated as handheld meters, lower CAT rating. Because they are held by the user and hence less of a danger to the user when they explode, and you generally won't use a bench meter on supply side mains stuff.

author: EEVblog
author_rank: Unknown
timestamp: January 17, 2016, 10:23:54 am
content: Quote from: Gyro on January 17, 2016, 10:22:48 amI still would have supplied HRC fuses, they aren't that expensive.Even some gear have them on the mains side, they aren't expensive.

author: wraper
author_rank: Unknown
timestamp: January 17, 2016, 10:30:46 am
content: Quote from: EEVblog on January 17, 2016, 10:23:01 amIIRC only one type of them are mains fuses. Others certainly are for input protection. This meter has CAT1 1000V and CAT2 300V

author: Kleinstein
author_rank: Super Contributor
timestamp: January 17, 2016, 11:07:17 am
content: If the meter huses HRC fuses inside, it would be nice to have a replacement. The fuses itself are not that expensive, but getting a single one of the right type may cause extra shipping costs and delay.However don't expect Rigol to beat Keysight or Flike in this respect - though it would be rather easy.Some could also be mains fuses, especially if different sizes are used for 110 and 230 V operation.Bench meters also have the space to have a cheap and a HRC fuse in series - so you normally one have to change the cheap one.

author: H.O
author_rank: Frequent Contributor
timestamp: January 17, 2016, 11:22:46 am
content: The included fuses are 125mA for the AC-power input and 250mA for the low current range, these can be changed without opening the instrument. The fuse for the 10A range is internal and no spare is supplied with the instrument. I don't know what type it is but I can open my 3068 tomorow and check.Are you (the OP) claiming that the fuses aren't OK considering the CAT rating of the instrument? I'm certainly not sticking my 6.5 digit bench multimeter across (or in series with) the 400V 3-phase supply comming into the house - something the DM3068 isn't rated to do.EDIT: There you go, the internal fuse for the 10A range, although not one of the beefy HRC fuses looks to be "more" than your standard 5x20mm glass fuse,

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 17, 2016, 12:11:58 pm
content: Quote from: EEVblog on January 17, 2016, 10:23:01 amMost bench meters are in larger, metal boxes, so an exploding fuse is far less likely to cause any external hazard than in a small (=limited volume) plastic handheld case, so no need for expensive fuses, at least to protect the user.The meter may come off worse from a Cat4 overload event due to flash damage, but I would think safety standards are only about protecting the user, not the equipment (providing it remains in a safe state).

author: try
author_rank: Regular Contributor
timestamp: January 17, 2016, 12:14:22 pm
content: PA0PBZ,thanks for posting that picture with the cover removed.Have they painted the fuse surface in white color or is it really one of the better fuses?The truth is hidden deeply in their service manual:[...1. FuseThe DM3068 has three types of fuse, which are: power fuse, current input fuseon the rear panel and internal current input fuse on the mainboard, theparameters are as follows:115V Power fuse: AC, 250V, T250mA, slow- melt, 5x20mm230V Power fuse: AC, 250V, T125mA, slow- melt, 5x20mmReplaceable 200mA current input fuse on the rear panel: AC, 250V, F500mA,quick-melt, 5x20mmInternal 10A current input fuse on the mainboard: AC, 250V, F10A, quick-melt,6x32mm...]I just looked up some parts from my ESKA catalogue to have an idea how much protection is available for a fuse sized 6,3mmx30mm (10A current input)632.128 FF 12,5A 500V 1.500A632.528 F12,5A 500V 1.000A632.028 F12,5A 250V 1.000AThere are higher extinguishing currents available but they are rated below 250V.This is far away from that 30kA extinquishing ability of HRC? fuses.Anyway, even if the current fuse setup may comply with today's regulations I would have expected better ones.Most probably the three bags correspond to mains 125V, mains 250V and 200mA current input.

author: TechItApart
author_rank: Contributor
timestamp: January 17, 2016, 02:09:27 pm
content: OK noob question here, what's the problem with not using HRC fuse?I know the HRC fuses are better at stopping high current but doesn't a normal fuse work fine most of the time? The HRC fuses are an order of magnitude (or two) more expensive than regular glass fuses so I can see why Rigol used them.

author: Brumby
author_rank: Unknown
timestamp: January 17, 2016, 02:26:58 pm
content: HRC stands for High Rupture Capacity.When you have a high energy failure (like a short across the mains) an ordinary glass fuse will literally explode sending glass shrapnel and sputtered fuse wire flying through whatever space it occupies. The mess is obvious, but it may also cause secondary damage and represents a higher risk of injury if it escapes the equipment case. A HRC fuse, on the other hand is far less likely to do this - and the fuse casing may even survive.

author: m98
author_rank: Frequent Contributor
timestamp: January 17, 2016, 02:36:21 pm
content: Can't see the problem here, as precision bench multimeters are mostly used for low power stuff. Why would you need HRC-fused inputs when working on some analog or digital circuits?

author: TechItApart
author_rank: Contributor
timestamp: January 17, 2016, 03:19:22 pm
content: Quote from: Brumby on January 17, 2016, 02:26:58 pmThanks for the clarification. If the product is well designed shouldn't the glass fuse be inside a plastic fuse holder though? I imagine that would reduce the carnage to a minimum. I see why people think the Rigol is bad though - cheaping out on fuses = probably cheaping out elsewhere too.

author: H.O
author_rank: Frequent Contributor
timestamp: January 17, 2016, 04:53:26 pm
content: On the DM3068, the 5x20mm glass fuses for the mains and for the low current range ARE in protective holders, accessible from the back of the instrument. The 10A fuse for the high current range is clearly a ceramic type fuse which has a higher rupture capacity than a normal glass fuse. It's not painted white....Of course, you can almost always do things "better" but I don't see the problem here. Cheaping out and cutting coreners is one thing, not gilding the lilly is another.

author: Monkeh
author_rank: Super Contributor
timestamp: January 17, 2016, 05:09:32 pm
content: It's a 6½ digit bench meter, not an industrial hand-held DMM. It has no need for giant fuses which waste space and drive the price up.

author: ataradov
author_rank: Super Contributor
timestamp: January 17, 2016, 08:31:34 pm
content: Quote from: H.O on January 17, 2016, 04:53:26 pmExactly.The metal parts could have been done from titanium, since it is better in all possible respects.People seem to remember a few "good" things to do and repeat them as a mantra regardless of a particular situation.

author: TheSteve
author_rank: Unknown
timestamp: January 17, 2016, 08:35:35 pm
content: Given the price difference between the DM3068 and the 34461A I'd really hope most people would save just a little longer and buy the Keysight. Then Rigol can use all the glass fuses they want...

author: electr_peter
author_rank: Unknown
timestamp: January 18, 2016, 06:38:57 pm
content: I do not see any problem with fuses at all. Rigol DMM in question is rated only for Cat I (1000V) and Cat II (300V) - similar rating as most bench 6.5 digit class DMMs. It is not supposed to be used on hazardous circuits - other appropriate DMMs are for that. And why would you want 6.5 digit DMM to measure AC mains, when, for example, most mains AC in EU is specified at 230V RMS+/- 10%?Glass fuses are appropriate here. Mains input fuse is also glass type, no issue here as well.If somebody is snobbish enough to put high cost (and hard to source) HRC fuses in anything then I suggest to fill whole DMM case with sand - HRC fuse is the same glass fuse with sand inside it after all...

author: commongrounder
author_rank: Frequent Contributor
timestamp: January 20, 2016, 06:19:25 pm
content: To expand on whatelectr_petersaid: There is more to HRC fuses than just minimizing damage from a shattered fuse case. HRC fuses have aninterruptrating. This means the ability to quench a high energy plasma arc during an overcurrent. Often these fuses are rated to quench a 10,000 amp arc, which would vaporize a regular fuse potentially causing a devastating arc flash inside (and probably outside) the meter case. That is why HRC fuses are so large for their capacity. They are filled with sand, which collapses in to the fuse element when it melts and quenches the arc. I think ceramic type fuses are suitable for bench meters. They, at least, won't shatter if a large, high voltage, capacitor were to accidentally discharge through them.

author: Nerull
author_rank: Frequent Contributor
timestamp: January 20, 2016, 08:29:57 pm
content: Which the meter has, making this whole thread moot.I do wonder what try is selling, though. New users don't sign up to slag off on a particular brand they don't own and have never seen for no reason.