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| What are - for you - the 3 biggest disadvantages of your benchtop DMM(s)? |
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| joeqsmith:
--- Quote from: tautech on September 02, 2020, 09:44:03 pm --- --- Quote from: bdunham7 on September 02, 2020, 09:27:42 pm --- --- Quote from: Fungus on September 02, 2020, 08:55:49 pm ---Nowhere in CAT documents does it say the the meter should survive. --- End quote --- The 8842A isn't actually 'CAT rated' as far as I know, at least neither CAT xx/yyyV or any reference to IEC1010 appears anywhere on it. I wonder when that started to be a thing--my earliest product that I can lay hands on that has a CAT rating insignia is my old Scopemeter--CAT III/600V. However, I don't think this was any type of CAT event. I think it was subjected to a severe overvoltage, not a transient. I think it is open for discussion as to whether the meter 'survived'. IMO it did survive--just a little more repair needed than replacing a fuse. --- End quote --- No it didn't survive, it needed to be repaired before further use. You saved it from going in a dumpster that's all. --- End quote --- We may think of a loved one who lived through all the treatments of cancer as surviving. However, I don't see it this way when it comes to test equipment. If it was exposed to an event that required repairs, it didn't survive. Rather I would say it was repairable or salvaged. |
| wizard69:
--- Quote from: Fungus on September 02, 2020, 08:55:49 pm --- --- Quote from: bdunham7 on September 02, 2020, 04:04:07 pm ---I just took apart an old 8842A that apparently was connected to excessive voltage--at least 1500V---with some power to back it up. The entire front end protection--4 MOVs and 2 fusible resistors--were incinerated. I removed the burnt parts and subbed in 2 regular 1K resistors (to be repaired properly later, of course) and the meter works properly and is in cal. No evidence of any external damage, the circuit board is unharmed (but sooty) and I'm sure nobody died. I'd say that is 'robust' although I can't quantify that. --- End quote --- Nowhere in CAT documents does it say the the meter should survive. --- End quote --- CAT is about keeping the user safe. The meter may not be functional but it shouldn't harm the user when an accident happens. |
| bdunham7:
--- Quote from: joeqsmith on September 03, 2020, 02:51:45 am ---If it was exposed to an event that required repairs, it didn't survive. Rather I would say it was repairable or salvaged. --- End quote --- OK, fair enough. I did say it was a debatable point. Would you say the same for a meter that required the replacement of an internal fuse after exposure to excess current? If not, then why would you have a different opinion when the items that 'failed' (actually they worked) are protective devices specifically intended for this purpose? Of course, I'll grant that the MOVs might not fall into the same category as the fusible resistors, incineration isn't their normal mode of operation. :o My gripe here isn't about the definition of 'survived', it is that the aversion to repairability is causing people to completely shun 'repairable' failure modes. Why have MOV protection when they could fail? Just let the CPU take the hit--after all dead is dead. I suppose that's true for cheap consumer products and things we send into space, but I don't think it should be for expensive instruments--at least where it is practical to build them otherwise. |
| tautech:
--- Quote from: bdunham7 on September 03, 2020, 01:36:03 am --- --- Quote from: tautech on September 02, 2020, 10:06:27 pm ---You repaired it to a condition that works for you, congrats and I mean that however for most that rely on a bench meter for trusted best possible accuracy they would bin it. Obtaining the equipment to verify its performance will cost more than replacing it. --- End quote --- Calibrating it would be part of a proper repair and I will certainly do a complete check at some point. I understand that the 'average user' doesn't have the means to check the performance, but my point is that in its day, this product would be sent in for service and calibration, not binned. New stuff, well that does get binned. But as far as trusting it, at least on the DCV ranges that I've checked so far, it is still more accurate toasted than any product your company sells brand new, so there's that. :) --- End quote --- Yes well I could tell you a horror story of a mate that recently bought a spanking new DMM6500 but I shouldn't. :-X Let's just say it got sent back to the US to get sorted and arrived back here in NZ still not right. ::) |
| joeqsmith:
--- Quote from: bdunham7 on September 03, 2020, 03:07:09 am --- --- Quote from: joeqsmith on September 03, 2020, 02:51:45 am ---If it was exposed to an event that required repairs, it didn't survive. Rather I would say it was repairable or salvaged. --- End quote --- OK, fair enough. I did say it was a debatable point. Would you say the same for a meter that required the replacement of an internal fuse after exposure to excess current? If not, then why would you have a different opinion when the items that 'failed' (actually they worked) are protective devices specifically intended for this purpose? Of course, I'll grant that the MOVs might not fall into the same category as the fusible resistors, incineration isn't their normal mode of operation. :o My gripe here isn't about the definition of 'survived', it is that the aversion to repairability is causing people to completely shun 'repairable' failure modes. Why have MOV protection when they could fail? Just let the CPU take the hit--after all dead is dead. I suppose that's true for cheap consumer products and things we send into space, but I don't think it should be for expensive instruments--at least where it is practical to build them otherwise. --- End quote --- In the case of the fuse, we are talking about a user serviceable component. Of course, you may consider all component user serviceable but that's not what I am referring to. The manuals for a meter will commonly detail how to test and replace the fuses, along with providing details about what to replace them with. In some cases, meters like my HP34401 and Fluke 8000A, the fuse (for the current measurement) can be accessed without opening the case. The fuse was designed to prevent damage to the user (say an arc flash) as well as protect the meter. Other parts, like MOVs, surge rated resistors.... are soldered in place. They are not called out in the manual as something the user should be servicing. If the only damage was the fuse, then I would say the fuse blew but the meter survived. Say some idiot uses the wrong fuse or even better, jumps the fuse they blew and then the meter is exposed to something that damages other components, I would say you not only damaged your meter but you were an idiot for not following the manufactures requirements. Once the parts are soldered into the board, they become part of a larger assembly and require special skills to service. Of course this doesn't prevent some people from attempting to do repairs they may not be qualified to do. Again, as we have seen in many posts, there are people who are not qualified to change a fuse. As to your comment about repairability, I imagine in cases where we have unqualified people working on safety equipment, we run into cases where they create an unsafe condition (say the person jumping the HRC fuse). If something were to happen, I would assume the manufacture will be named on the suit. We may see a time when fuses are no longer user serviceable. As I said, the MOVs, PTC, GDTs, surge rated resistors, high speed clamps that you find are there to try and make the meter more robust so it survives various events the user exposes the DMM to. If we exceed the limits of what any of these combined parts can handle, we have damaged the meter. If we can salvage or repair it, comes down to the cost/time. If these parts save the downstream ICs, then I will typically repair them. If not, they are normally scrapped. |
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