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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#41
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Analogue moving coil meter range extension?
On Thu, 21 Sep 2017 17:21:23 -0700, mike wrote:
Words like exactly, "as good as possible" have no place in a specification. a common enough phrase for an in-house spec. Such phrases should be cleared up later of course, once the specifier knows what the engineers can actually do and what the options cost. Specs are numbers and test methods. Specs include allowable variations due to initial component tolerances, component age, temperature, vibration, misuse. Some do. Some are 'how can you get it as cheap as possible and still have it sell & not destroy our repuation.' Some are 'we want to beat what's out there, how good could you get it?' Some are 'we want it to do this.' etc etc etc. The 'human' bit: A small (key fact) analogue (key fact) panel meter connected to a lead acid battery (key fact) needs reading and those readings interpreting and so ITRW, we are 'most likely' to not require much in the way of precision or we wouldn't be using those things in the first place. ;-) 1% is doable for some analogue meters. That's enough precision for a lot of tasks. NT |
#43
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Analogue moving coil meter range extension?
mike wrote:
On 9/21/2017 8:13 PM, tabbypurr wrote: End rant. He's making a one off for use at home, not commissioning a new design of military hardware. The task is the same no matter who the customer. At least the extra option should be there. |
#44
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Analogue moving coil meter range extension?
On Fri, 22 Sep 2017 15:38:26 -0700 (PDT), wrote:
On Friday, 22 September 2017 05:05:35 UTC+1, Jeff Liebermann wrote: On Thu, 21 Sep 2017 20:59:03 -0700 (PDT), tabbypurr wrote: simple but time consuming producing a new dial paper "The Windows programs for drawing analog meter scales" http://www.tonnesoftware.com/meter.html $35 for the full version. fails to solve the issue AND adds pointless cost. NT The consensus seems to be to use an expanded scale analog voltmeter. If the OP is going to build such a thing, he needs a new scale on his analog meter. That can be done with the free version of the software. (I just checked and it will do an expanded scale). I usually ignore one line pontifications, but I'm curious. Why does a new meter scale fail to solve the issue? Ummm... what issue? -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#45
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Analogue moving coil meter range extension?
On Fri, 22 Sep 2017 15:39:14 -0700 (PDT), wrote:
On Friday, 22 September 2017 05:22:46 UTC+1, Foxs Mercantile wrote: On 9/21/2017 10:59 PM, tabbypurr wrote: simple but time consuming producing a new dial paper With the low current Zener, it doesn't look like that will be necessary. Oh, you've found a zener that's 10v +/- 1%? NT The meter isn't even that accurate. You're not going to be able to read the meter to +/- 0.1V. Also, I coulnd't find where anyone specified the accuracy required. If you really want 1% accuracy, maybe a 10.0V precision reference, such as the TI REF102: http://www.ti.com/lit/ds/symlink/ref102.pdf However, there's a problem. The IC requires a V+ of 11.4-36VDC which will probably require a battery or other power supply. Hmmm... I sorta blundered across this idea: http://www.qsl.net/kh6grt/page4/expscale/expscale.htm It doesn't expand the entire meter scale from 10-15VDC. Instead, it compresses 0-10V into a small part of the meter scale, and expands the 10-15V over the rest of the scale. However, it requires +12v and -12v power. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#46
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Analogue moving coil meter range extension?
On Saturday, 23 September 2017 17:35:36 UTC+1, Jeff Liebermann wrote:
On Fri, 22 Sep 2017 15:38:26 -0700 (PDT), tabbypurr wrote: On Friday, 22 September 2017 05:05:35 UTC+1, Jeff Liebermann wrote: On Thu, 21 Sep 2017 20:59:03 -0700 (PDT), tabbypurr wrote: simple but time consuming producing a new dial paper "The Windows programs for drawing analog meter scales" http://www.tonnesoftware.com/meter.html $35 for the full version. fails to solve the issue AND adds pointless cost. NT The consensus seems to be to use an expanded scale analog voltmeter. that's part of the spec If the OP is going to build such a thing, he needs a new scale on his analog meter. yes That can be done with the free version of the software. (I just checked and it will do an expanded scale). it can I usually ignore one line pontifications, but I'm curious. Why does a new meter scale fail to solve the issue? Ummm... what issue? The issue with using an inaccurate zener is that the meter scale most likely won't run from 10.0v, and will thus need calibrating over its scale. That also means a new scale with marks in new places - a pita to do. Far easier to knock off 10v exactly then just change the numbers on the scale. NT |
#47
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Analogue moving coil meter range extension?
On Saturday, 23 September 2017 17:52:35 UTC+1, Jeff Liebermann wrote:
On Fri, 22 Sep 2017 15:39:14 -0700 (PDT), tabbypurr wrote: On Friday, 22 September 2017 05:22:46 UTC+1, Foxs Mercantile wrote: On 9/21/2017 10:59 PM, tabbypurr wrote: simple but time consuming producing a new dial paper With the low current Zener, it doesn't look like that will be necessary. Oh, you've found a zener that's 10v +/- 1%? NT The meter isn't even that accurate. We don't know the meter's accuracy. 1% is common enough, but it might be worse. (For all we know it might even be a moving iron thing.) You're not going to be able to read the meter to +/- 0.1V. Even my most rock bottom multimeters, under $3 each new, are easy to read to 1%. Decent meters do much better. Also, I coulnd't find where anyone specified the accuracy required. If you really want 1% accuracy, maybe a 10.0V precision reference, such as the TI REF102: http://www.ti.com/lit/ds/symlink/ref102.pdf However, there's a problem. The IC requires a V+ of 11.4-36VDC which will probably require a battery or other power supply. Hmmm... I sorta blundered across this idea: http://www.qsl.net/kh6grt/page4/expscale/expscale.htm It doesn't expand the entire meter scale from 10-15VDC. Instead, it compresses 0-10V into a small part of the meter scale, and expands the 10-15V over the rest of the scale. However, it requires +12v and -12v power. Nice idea, though I don't expect the op needs it. I'm sure one could design a circuit that can use opamps that are happy on the 10-15v and halve V_in. NT |
#48
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Analogue moving coil meter range extension?
On 9/22/2017 1:29 AM, T i m wrote:
On Thu, 21 Sep 2017 21:41:44 -0700, mike wrote: On 9/21/2017 8:13 PM, wrote: End rant. He's making a one off for use at home, not commissioning a new design of military hardware. The task is the same no matter who the customer. It can and maybe should be, in an ideal world. I say that because I hate having to deal with 'fools who rush in' or those expecting me to make technical / choice decisions on their behalf (like getting them some 'size 10, brown, lace up leather shoes'). ;-( The more steps you skip, the more problems you have. 'May have'. The more you think like a project manager, the better managed your home projects. Agreed. I like to understand as much about something as I can. However, my ability to do so, time available to do so and the pertinence of doing so don't always allow me to do so or to do so to the level I would like. Sometimes you just have to get stuck in. ;-) Once you acquire the habit, you'll find that it adds little to the time in the beginning and greatly simplifies the end. Agreed 100%. And it wastes far less time for rocket scientists in residence. Quite ... however, this is a 'discussion' group and so does have an element of that, along with the hard science / fact stuff. Part of the 'human' bit is not making a post (especially the initial one) too long (I fail most of the time) as it will put people off reading it and if there were any further points that need refining they could be done with a simple Q&A. e.g. I initially outlined the fairly close detail at a level relevant to my needs and understanding (IMHO anyway). I didn't expand on what I was going to actually use it for because it didn't really matter to the question. I left it open to the reader to ask any supplementary questions as they felt relevant. ;-) Cheers, T i m Metrology is an interesting topic. When someone asks me how to measure something, my first thought is, "exactly how will the answer to your question improve YOUR life tomorrow?" Sometimes I actually say it. The "jolt" to their thought process forces them to express what they're trying to accomplish...or admit to themselves that they have no idea. I find that almost all questions end up in the "won't affect them at all" category and I can dispense with trying to teach them something they'll never use. If the answer won't change the future, don't bother with the question. It's similar to pointless social interaction. People you don't know ask questions, like "how are you?" They think they know what you'll say. Respond with something like, "I have this rash on my dick and think I need to find a different street corner... got any ideas?" to see how much they really care about how you are. ;-) But I digress... If I had an electric boat, the ability to measure voltage to six decimal places would not be my priority. What I want to know is, "can I get back to the dock?" You can do that more accurately with a sharpie and nonlinear meter than you can react to a change in wind direction. The river current and wind and the shape of the curve of distance covered vs velocity and temperature would be far more important variables to me. Amp hours consumed would be important. Battery voltage that would be strongly impacted by whether I'm going up or down stream at what net velocity is a poor substitute. An integrating current meter, a water speed speedometer and a GPS would much more interesting. If you knew the water flow direction and speed, you probably wouldn't have to measure anything else other than what you can get from the GPS. Drifting downstream for a minute would give you those two numbers. But, since you're dead set on measuring voltage... The basic problem is that the voltage you want to measure is the biggest voltage you have to power your circuit. That's why I split my original post into the concept (battery) and the implementation (zener). A series zener needs to draw ZERO current at 10V and still be 10V at MUCH higher current ratio. You will have to live with some amount of nonlinearity. You could stack an AA-cell or two on top of your battery system and alleviate that problem. I maintain that a digital voltmeter is the best option. They're dirt cheap on EBAY. All the above is based on an extreme extrapolation of very limited information. That's why the system spec is so important. |
#49
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Analogue moving coil meter range extension?
On Sunday, 24 September 2017 12:06:45 UTC+1, mike wrote:
A series zener needs to draw ZERO current at 10V and still be 10V at MUCH higher current ratio. You will have to live with some amount of nonlinearity. In fact you could re-zero the meter so it reads 10v spot on. Add an extra mark for where it points when unpowered so you can see if it ever decalibrates. You could stack an AA-cell or two on top of your battery system and alleviate that problem. yuck. 2 resistors beats 2 cells any day. I maintain that a digital voltmeter is the best option. They're dirt cheap on EBAY. but noncompliant with the basic spec NT |
#50
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Analogue moving coil meter range extension?
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#51
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Analogue moving coil meter range extension?
On Monday, 25 September 2017 01:53:43 UTC+1, mike wrote:
On 9/24/2017 6:31 AM, tabbypurr wrote: On Sunday, 24 September 2017 12:06:45 UTC+1, mike wrote: A series zener needs to draw ZERO current at 10V and still be 10V at MUCH higher current ratio. You will have to live with some amount of nonlinearity. In fact you could re-zero the meter so it reads 10v spot on. Add an extra mark for where it points when unpowered so you can see if it ever decalibrates. Yes, you can , but it's still nonlinear. It's a matter of how much nonlinearity you can tolerate. It's my assertion that the measured quantity is so crude that you don't need to worry much about anything. Just learn what it reads and calibrate your expectations to match. You could stack an AA-cell or two on top of your battery system and alleviate that problem. yuck. 2 resistors beats 2 cells any day. Can't argue with that assertion, but, if you can provide a circuit that is precisely linear and accurate over the WHOLE range using two resistors, I'd like to see it. I'm betting it's more than two resistors. What I meant is divide the input to your opamp so it's away from the rails and you don't need any rail boosting. NT |
#52
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Analogue moving coil meter range extension?
On Sun, 24 Sep 2017 17:52:51 -0700, mike wrote:
On 9/24/2017 6:31 AM, wrote: On Sunday, 24 September 2017 12:06:45 UTC+1, mike wrote: A series zener needs to draw ZERO current at 10V and still be 10V at MUCH higher current ratio. You will have to live with some amount of nonlinearity. In fact you could re-zero the meter so it reads 10v spot on. Add an extra mark for where it points when unpowered so you can see if it ever decalibrates. Yes, you can , but it's still nonlinear. It's a matter of how much nonlinearity you can tolerate. It's my assertion that the measured quantity is so crude that you don't need to worry much about anything. Just learn what it reads and calibrate your expectations to match. (I've been a bit preoccupied elsewhere but still following the thread with interest and will reply individually when I get the chance) That was part I had already considered in that: The meter is fairly small. The meter is glued shut. The meter is only marked in whole volts. So, as you say, afa this experiment is concerned it was a cheap toe-dipping into the concept of meter range enhancement, partly because I think analogue display still have some merit and partly for the S&G's. ;-) snip I try to adjust expectations to meet the ACTUAL requirements before delving into complex solutions to implement a nonsense requirement. In this case the actual requirements were fairly simplistic as it was an experiment. A feasibility study if you will. As you say, a DMM can be bought for next to nothing (and I have several and one I'm already using) but that wasn't the (entire) point. Yes, the customer is always right. My job is to alert him to the consequences of his demands. ;-) Another non-complient solution is to use the two resistors and a zener to make a 9V-15V meter and hope that most of the nonlinearity of the two resistor solution happens in the 9-10V range. With a very small buck converter you could get a higher voltage supply to ensure a voltage reference of some sort had sufficient overhead to work correctly when close to the 10V threshold? That way, the characteristics of the zener knee are important over a 5:1 current range instead of an infinite ratio. ITRW, as long as it's starting to work reasonably by 10.5V it shouldn't really be an issue. I'm far too lazy to do the math on how nonlinear it will be. I do like the idea of printing my own scale and if this basic one works, I might go for a bigger / better meter that I can open etc. There's also an elephant in the room. Unless you start with a meter that happens to have scale markings ranging from 10 to 15, you're gonna need a new scale no matter what you do with the electronics. Unless it's already marked 0, 1, 2, 3, 4 and 5 'Volts' and you know just have to add 10 to all of them. I would imaging the needle pointing up the middle to 12.x would be a sufficient comforter. ;-) If you're not gonna do that, might as well just mark calibrations on the face with a sharpie. Only if I can get the thing open and it wouldn't be worth damaging it to try. Makes no sense to go to great lengths in one part of the project only to create something that still doesn't do what you want. My only hope is that it works 'better' than a similarly sized and accuracy meter that is marked 0 to 15 and using it over a tiny proportion of the range. As has been suggested, if you aren't happy to try to KISS then you are then going to be worrying about thermal stability and scale linearity and I'd like to leave that for the Mk2. ;-) Cheers, T i m |
#53
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Analogue moving coil meter range extension?
On Fri, 22 Sep 2017 14:13:13 -0700 (PDT), whit3rd
wrote: On Thursday, September 21, 2017 at 10:51:33 AM UTC-7, T i m wrote: Hi All, Not a 'repair' question as such but I was thinking of using an old skool 250uA FSD moving coil panel meter to read the 10 to 15V DC range (a lead acid battery charge / discharge indicator), next to a 0-30A Ammeter (inc shunt etc). I was thinking of using either a voltage reference such as LM4040DIZ-10.0 or could I get away with a simple zener (BZX55C?) with associated resistor(s) please? You can use any zener under 10V to do a 10V zero offset (just divide down the input voltage until that 10V input matches the zener knee). So, with an arbitrary zener (I'd use a TL431 as a 2.5V reference, they're convenient and accurate) and a trimmer acting as voltage divider, it just remains to make a range-setting resistor in series with the meter. Hmm, that's crafty. ;-) I'm trying to picture how the voltage rise would still be linear but I think I can see how it would be. The -ve of the meter is held at some voltage threshold low enough to ensude a low change in difference between the voltage measured and the ground. A variable (to start with at least) resistor set as a pd then sets the upper voltage to give FSD at 15V. The important thing, is to doodle up a really nifty scale for your meter that indicates 10V to 15V, with clear markings, along the pointer's arc, maybe with a bunch of subdivision marks. Yeah, that sounds like a interesting project for a Mk2 meter. ;-) took a plotter and a bit of custom software to draw the arcs and labels, I saw the link to some free software for doing such but not had chance to try it yet. then some fiddling with the faceplate of the meter to affix it (warning: you need to worry about laser-print ink, paper, glue compatibility). Ok. ;-) Cheers, T i m |
#54
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Analogue moving coil meter range extension?
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#55
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Analogue moving coil meter range extension?
On Fri, 22 Sep 2017 10:53:54 -0500, "Dave M"
wrote: snip I forgot to mention that for the zener solution, you really need to select as low power a zener that you can find, such as 400mW or lower. The 1N4104 is a 10V, 250mW zener, with a test current of 1uA, and a max current of 25ma, well within your requirements. In stock at Mouser.com. Cheers, Dave, I'll have a look. As has been mentioned elsewhere, if we used a lower voltage zener (and as high a tolerance as can be found in the right spec and the right price *because*) to set the voltage on the -Ve leg of the meter and then tweak the voltage up via resistors (variable initially) to give a FSD at 15V then that should be sufficient? I can't help feeling I've missed something with that solution though, like the linearity ... ? ;-( Cheers, T i m |
#56
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Analogue moving coil meter range extension?
On Monday, 25 September 2017 04:43:06 UTC+1, T i m wrote:
On Sun, 24 Sep 2017 17:52:51 -0700, mike wrote: On 9/24/2017 6:31 AM, tabbypurr wrote: On Sunday, 24 September 2017 12:06:45 UTC+1, mike wrote: A series zener needs to draw ZERO current at 10V and still be 10V at MUCH higher current ratio. You will have to live with some amount of nonlinearity. In fact you could re-zero the meter so it reads 10v spot on. Add an extra mark for where it points when unpowered so you can see if it ever decalibrates. Yes, you can , but it's still nonlinear. It's a matter of how much nonlinearity you can tolerate. It's my assertion that the measured quantity is so crude that you don't need to worry much about anything. Just learn what it reads and calibrate your expectations to match. (I've been a bit preoccupied elsewhere but still following the thread with interest and will reply individually when I get the chance) That was part I had already considered in that: The meter is fairly small. The meter is glued shut. The meter is only marked in whole volts. If it's not an accurate meter just add a zener, job done. NT |
#57
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Analogue moving coil meter range extension?
On Monday, 25 September 2017 10:01:42 UTC+1, mike wrote:
On 9/24/2017 6:05 PM, tabbypurr wrote: On Monday, 25 September 2017 01:53:43 UTC+1, mike wrote: On 9/24/2017 6:31 AM, tabbypurr wrote: On Sunday, 24 September 2017 12:06:45 UTC+1, mike wrote: A series zener needs to draw ZERO current at 10V and still be 10V at MUCH higher current ratio. You will have to live with some amount of nonlinearity. In fact you could re-zero the meter so it reads 10v spot on. Add an extra mark for where it points when unpowered so you can see if it ever decalibrates. Yes, you can , but it's still nonlinear. It's a matter of how much nonlinearity you can tolerate. It's my assertion that the measured quantity is so crude that you don't need to worry much about anything. Just learn what it reads and calibrate your expectations to match. You could stack an AA-cell or two on top of your battery system and alleviate that problem. yuck. 2 resistors beats 2 cells any day. Can't argue with that assertion, but, if you can provide a circuit that is precisely linear and accurate over the WHOLE range using two resistors, I'd like to see it. I'm betting it's more than two resistors. What I meant is divide the input to your opamp Thereyougo...opamp is a lot more complex than two resistors...or a couple of AA cells. I'm pretty sure we all know that, and what the options are, and what the pros & cons are. And that adding AA cells rather than 2 resistors on the input is not an option with any upside. NT |
#58
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Analogue moving coil meter range extension?
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#59
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Analogue moving coil meter range extension?
On Monday, 25 September 2017 12:37:05 UTC+1, T i m wrote:
On Mon, 25 Sep 2017 03:41:49 -0700 (PDT), tabbypurr wrote: snip That was part I had already considered in that: The meter is fairly small. The meter is glued shut. The meter is only marked in whole volts. If it's not an accurate meter just add a zener, job done. Well, I'm not sure if it's electro mechanically any more or less 'accurate' than any similar style meters and being smaller with a shorter / lighter needle it's possible it could be better than some ... but regarding the potential display markings and readability, you may well be right. ;-) Cheers, T i m If it's only marked in whole volts, reading it with accuracy won't happen, so it won't be especially accurate. NT |
#60
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Analogue moving coil meter range extension?
On Monday, September 25, 2017 at 10:13:48 AM UTC-4, wrote:
If it's only marked in whole volts, reading it with accuracy won't happen, so it won't be especially accurate. How so? I suggest that you are mistaking "accuracy" for "precision". They are not even a little bit the same thing nor follow necessarily one from another. A gauge or meter that reads (is marked) in whole numbers but is dead-on is far more accurate than a gauge or meter marked in thousandths, but is always two units off. Although the latter meter is extremely precise. I have a metered Iso-Variac that reads in volts measured in tens, and amps measured in tenths on a 0 -1 or 0 - 4 scale. But they are 4" meters so that even very slight needle movements are visible. The human brain is pretty good at interpolation. Peter Wieck Melrose Park, PA |
#61
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Analogue moving coil meter range extension?
T i m wrote:
On Fri, 22 Sep 2017 10:53:54 -0500, "Dave M" wrote: snip I forgot to mention that for the zener solution, you really need to select as low power a zener that you can find, such as 400mW or lower. The 1N4104 is a 10V, 250mW zener, with a test current of 1uA, and a max current of 25ma, well within your requirements. In stock at Mouser.com. Cheers, Dave, I'll have a look. As has been mentioned elsewhere, if we used a lower voltage zener (and as high a tolerance as can be found in the right spec and the right price *because*) to set the voltage on the -Ve leg of the meter and then tweak the voltage up via resistors (variable initially) to give a FSD at 15V then that should be sufficient? I can't help feeling I've missed something with that solution though, like the linearity ... ? ;-( Cheers, T i m I gave the wrong zener current for the 1N4104 . I just looked at Mouser's basic info for the diode, but neglected to follow up and look at the actual datasheet. According to the datasheet, the zener test current is actually 250uA, whereas Mouser states it as 1uA. Quite a difference, but after looking at the datasheets for some other 10V/200mW zeners, (datasheets that had actual graphs for Iz vs. Vz) I see that they actually start conducting well below 1uA, so I feel confident that the 1N4104 will do the job for you. All the other zeners that I found are SMD devices, so I doubt that you'll be interested in any of those. With that Zener in the circuit, I doubt that you'll have any noticible nonlinearity; certainly not with the meter scale only having a 1-volt resolution. Forget about the accuracy on the low end as well (except at the volt marks), because you can't resolve to a basic meter accuracy specification of +-3% of FSD. Dave M |
#62
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Analogue moving coil meter range extension?
On Mon, 25 Sep 2017 07:53:49 -0700 (PDT), "
wrote: On Monday, September 25, 2017 at 10:13:48 AM UTC-4, wrote: If it's only marked in whole volts, reading it with accuracy won't happen, so it won't be especially accurate. How so? I suggest that you are mistaking "accuracy" for "precision". They are not even a little bit the same thing nor follow necessarily one from another. +1 A gauge or meter that reads (is marked) in whole numbers but is dead-on is far more accurate than a gauge or meter marked in thousandths, but is always two units off. Yup, that's the thing ... and why many battery meters are calibrated with red, amber and green sections. Now whilst that would work for me re charge (voltage) and loosely therefore charge status, it wouldn't be useful to pin down the discharge / charge status (unlike say a CCA tester) as the terminal volts are a function of load. Although the latter meter is extremely precise. Yup and I have some of those. Highly repeatable but always 'out' by some amount. ;-( I have a metered Iso-Variac that reads in volts measured in tens, and amps measured in tenths on a 0 -1 or 0 - 4 scale. But they are 4" meters so that even very slight needle movements are visible. The human brain is pretty good at interpolation. And it was the latter thought that I was using when it came to this meter. ;-) Take something that offers a very 'human' way of displaying something (like an analogue car fuel or specifically, temperature gauge that starts at say 60 DegC) and retain the merits but improve the general meaning / readability. Mileage / trip counters are more suited to being 'digital' etc. ;-) Cheers, T i m |
#63
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Analogue moving coil meter range extension?
On Monday, 25 September 2017 15:53:59 UTC+1, wrote:
On Monday, September 25, 2017 at 10:13:48 AM UTC-4, tabby wrote: If it's only marked in whole volts, reading it with accuracy won't happen, so it won't be especially accurate. How so? I suggest that you are mistaking "accuracy" for "precision". They are not even a little bit the same thing nor follow necessarily one from another. A gauge or meter that reads (is marked) in whole numbers but is dead-on is far more accurate than a gauge or meter marked in thousandths, but is always two units off. Although the latter meter is extremely precise. I have a metered Iso-Variac that reads in volts measured in tens, and amps measured in tenths on a 0 -1 or 0 - 4 scale. But they are 4" meters so that even very slight needle movements are visible. The human brain is pretty good at interpolation. Peter Wieck Melrose Park, PA With very coarse markings you won't get accurate readings. End of relevant material. I have no motivation to argue over the simple and immaterial. NT |
#64
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Analogue moving coil meter range extension?
On 9/25/2017 3:35 PM, Dave M wrote:
I see that they actually start conducting well below 1uA, so I feel confident that the 1N4104 will do the job for you. All the other zeners that I found are SMD devices, so I doubt that you'll be interested in any of those. Previously I wrote: The simplest is a 20K resistor in series with a 10v zener diode. Use a low current Zener so the knee works right at low values. Something like this: http://www.mouser.com/ds/2/395/BZX55C2V0%20SERIES_D1610-1099630.pdf Note, this is a DO-35 package. -- Jeff-1.0 wa6fwi http://www.foxsmercantile.com |
#65
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Analogue moving coil meter range extension?
On Sunday, September 24, 2017 at 8:43:06 PM UTC-7, T i m wrote:
On Sun, 24 Sep 2017 17:52:51 -0700, mike wrote: I'm far too lazy to do the math on how nonlinear it will be. I do like the idea of printing my own scale and if this basic one works, I might go for a bigger / better meter that I can open etc. Yep, that's a good idea. And, there's NO NONLINEARITY unless you apply bias less than the zener voltage breakdown, because of Norton's theorem: any bunch of resistors and voltage sources (the zener is a voltage source) is identically a current source with a shunt resistance. Offset by a constant, you can get; nonlinearity, you can't. The meter magnetic field is the only source of nonlinearity (and meter manufacturers do pretty well on keeping that uniform). |
#66
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Analogue moving coil meter range extension?
On Tuesday, 26 September 2017 03:21:57 UTC+1, whit3rd wrote:
On Sunday, September 24, 2017 at 8:43:06 PM UTC-7, T i m wrote: On Sun, 24 Sep 2017 17:52:51 -0700, mike wrote: I'm far too lazy to do the math on how nonlinear it will be. I do like the idea of printing my own scale and if this basic one works, I might go for a bigger / better meter that I can open etc. Yep, that's a good idea. And, there's NO NONLINEARITY unless you apply bias less than the zener voltage breakdown, because of Norton's theorem: any bunch of resistors and voltage sources (the zener is a voltage source) is identically a current source with a shunt resistance. Offset by a constant, you can get; nonlinearity, you can't. The meter magnetic field is the only source of nonlinearity (and meter manufacturers do pretty well on keeping that uniform). zener v/i curves vary, some are terrible near zero i, some straighter. NT |
#67
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Analogue moving coil meter range extension?
On Mon, 25 Sep 2017 20:08:01 -0500, Foxs Mercantile
wrote: On 9/25/2017 3:35 PM, Dave M wrote: I see that they actually start conducting well below 1uA, so I feel confident that the 1N4104 will do the job for you. All the other zeners that I found are SMD devices, so I doubt that you'll be interested in any of those. Previously I wrote: The simplest is a 20K resistor in series with a 10v zener diode. Use a low current Zener so the knee works right at low values. Something like this: http://www.mouser.com/ds/2/395/BZX55C2V0%20SERIES_D1610-1099630.pdf Note, this is a DO-35 package. So, if the / any issue to the zener solution is the closeness of any knee to the bottom end of the required voltage range, would the using the / a lower reference and a potential devider to set the fsd on 15 volts be a better idea still (or have I missed something again)? ;-( Cheers, T i m |
#68
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Analogue moving coil meter range extension?
On Mon, 25 Sep 2017 15:35:28 -0500, "Dave M"
wrote: T i m wrote: On Fri, 22 Sep 2017 10:53:54 -0500, "Dave M" wrote: snip I forgot to mention that for the zener solution, you really need to select as low power a zener that you can find, such as 400mW or lower. The 1N4104 is a 10V, 250mW zener, with a test current of 1uA, and a max current of 25ma, well within your requirements. In stock at Mouser.com. Cheers, Dave, I'll have a look. As has been mentioned elsewhere, if we used a lower voltage zener (and as high a tolerance as can be found in the right spec and the right price *because*) to set the voltage on the -Ve leg of the meter and then tweak the voltage up via resistors (variable initially) to give a FSD at 15V then that should be sufficient? I can't help feeling I've missed something with that solution though, like the linearity ... ? ;-( I gave the wrong zener current for the 1N4104 . I just looked at Mouser's basic info for the diode, but neglected to follow up and look at the actual datasheet. According to the datasheet, the zener test current is actually 250uA, whereas Mouser states it as 1uA. Quite a difference, but after looking at the datasheets for some other 10V/200mW zeners, (datasheets that had actual graphs for Iz vs. Vz) I see that they actually start conducting well below 1uA, so I feel confident that the 1N4104 will do the job for you. Thanks for the follow up Dave. All the other zeners that I found are SMD devices, so I doubt that you'll be interested in any of those. Well, I have worked with SMD's but a wired device and could use on at a pinch (soldered to the side of the meter contact etc) bit a wired device is probably easier. With that Zener in the circuit, I doubt that you'll have any noticible nonlinearity; certainly not with the meter scale only having a 1-volt resolution. Forget about the accuracy on the low end as well (except at the volt marks), because you can't resolve to a basic meter accuracy specification of +-3% of FSD. Understood. I was thinking more on the idea of when using a lower voltage zener to be well clear of the lower voltage levels being considered and then the potential divider to set the FSD when the input is 15V? And also, wouldn't the impact of the battery voltage changing from say 10.5 to 14.4V be lessened (re the series current limiting / biasing resistor) if the voltage difference between the reference and the supply is greater? That seemed like the best of all worlds (for the KISS solution)? Cheers, T i m |
#69
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Analogue moving coil meter range extension?
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#70
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Analogue moving coil meter range extension?
On Tuesday, 26 September 2017 10:07:36 UTC+1, T i m wrote:
On Mon, 25 Sep 2017 15:35:28 -0500, "Dave M" wrote: T i m wrote: On Fri, 22 Sep 2017 10:53:54 -0500, "Dave M" wrote: snip I forgot to mention that for the zener solution, you really need to select as low power a zener that you can find, such as 400mW or lower. The 1N4104 is a 10V, 250mW zener, with a test current of 1uA, and a max current of 25ma, well within your requirements. In stock at Mouser.com. Cheers, Dave, I'll have a look. As has been mentioned elsewhere, if we used a lower voltage zener (and as high a tolerance as can be found in the right spec and the right price *because*) to set the voltage on the -Ve leg of the meter and then tweak the voltage up via resistors (variable initially) to give a FSD at 15V then that should be sufficient? I can't help feeling I've missed something with that solution though, like the linearity ... ? ;-( I gave the wrong zener current for the 1N4104 . I just looked at Mouser's basic info for the diode, but neglected to follow up and look at the actual datasheet. According to the datasheet, the zener test current is actually 250uA, whereas Mouser states it as 1uA. Quite a difference, but after looking at the datasheets for some other 10V/200mW zeners, (datasheets that had actual graphs for Iz vs. Vz) I see that they actually start conducting well below 1uA, so I feel confident that the 1N4104 will do the job for you. Thanks for the follow up Dave. All the other zeners that I found are SMD devices, so I doubt that you'll be interested in any of those. Well, I have worked with SMD's but a wired device and could use on at a pinch (soldered to the side of the meter contact etc) bit a wired device is probably easier. With that Zener in the circuit, I doubt that you'll have any noticible nonlinearity; certainly not with the meter scale only having a 1-volt resolution. Forget about the accuracy on the low end as well (except at the volt marks), because you can't resolve to a basic meter accuracy specification of +-3% of FSD. Understood. I was thinking more on the idea of when using a lower voltage zener to be well clear of the lower voltage levels being considered and then the potential divider to set the FSD when the input is 15V? And also, wouldn't the impact of the battery voltage changing from say 10.5 to 14.4V be lessened (re the series current limiting / biasing resistor) if the voltage difference between the reference and the supply is greater? That seemed like the best of all worlds (for the KISS solution)? Cheers, T i m You want a zener with a nice straight line at the low current end. One linked to from here has that. NT |
#71
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Analogue moving coil meter range extension?
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#72
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Analogue moving coil meter range extension?
On 9/26/2017 11:26 AM, T i m wrote:
On Tue, 26 Sep 2017 06:46:01 -0700 (PDT), wrote: You want a zener with a nice straight line at the low current end. One linked to from here has that. Yeah, ok ... but what about the question re using a lower value zener to get it away from the 'knee', especially as it's no more difficult to do? Here it is again. The simplest is a 20K resistor in series with a 10v zener diode. Use a low current Zener so the knee works right at low values. Something like this: http://www.mouser.com/ds/2/395/BZX55C2V0%20SERIES_D1610-1099630.pdf Note, this is a DO-35 package. -- Jeff-1.0 wa6fwi http://www.foxsmercantile.com |
#73
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Analogue moving coil meter range extension?
On 9/26/2017 9:26 AM, T i m wrote:
On Tue, 26 Sep 2017 06:46:01 -0700 (PDT), wrote: snip Understood. I was thinking more on the idea of when using a lower voltage zener to be well clear of the lower voltage levels being considered and then the potential divider to set the FSD when the input is 15V? And also, wouldn't the impact of the battery voltage changing from say 10.5 to 14.4V be lessened (re the series current limiting / biasing resistor) if the voltage difference between the reference and the supply is greater? That seemed like the best of all worlds (for the KISS solution)? You want a zener with a nice straight line at the low current end. One linked to from here has that. Yeah, ok ... but what about the question re using a lower value zener to get it away from the 'knee', especially as it's no more difficult to do? Cheers, T i m Since we're just trying to be clever, Try this: https://i.imgur.com/irLisN7.jpg The transistor and zener make a temperature compensated ~7V reference (must use 6.2V zener with standard tempco). Two pots set the min and max voltages. Rk allows you to add current to the zener to get it past the most nonlinear portion of it's V-I curve. This circuit has the ability to calibrate out almost any component variation. It's relatively temperature independent. You can use any meter that will make full scale at less than about 7V. Downside is that the pots are vibration sensitive and subject to moisture/corrosion. Are we having fun yet? |
#74
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Analogue moving coil meter range extension?
On Tuesday, 26 September 2017 17:26:46 UTC+1, T i m wrote:
On Tue, 26 Sep 2017 06:46:01 -0700 (PDT), tabbypurr wrote: snip Understood. I was thinking more on the idea of when using a lower voltage zener to be well clear of the lower voltage levels being considered and then the potential divider to set the FSD when the input is 15V? And also, wouldn't the impact of the battery voltage changing from say 10.5 to 14.4V be lessened (re the series current limiting / biasing resistor) if the voltage difference between the reference and the supply is greater? That seemed like the best of all worlds (for the KISS solution)? You want a zener with a nice straight line at the low current end. One linked to from here has that. Yeah, ok ... but what about the question re using a lower value zener to get it away from the 'knee', especially as it's no more difficult to do? Cheers, T i m The zeners with the straightest knee are at 9-10v. Go look at the linked data sheets. NT |
#75
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Analogue moving coil meter range extension?
On Tue, 26 Sep 2017 14:13:20 -0700, mike wrote:
snip Yeah, ok ... but what about the question re using a lower value zener to get it away from the 'knee', especially as it's no more difficult to do? Since we're just trying to be clever, I'm not mike, I'm just trying to refine the design of any solution to be as good as possible with the fewest possible components. ;-) Try this: https://i.imgur.com/irLisN7.jpg The transistor and zener make a temperature compensated ~7V reference (must use 6.2V zener with standard tempco). Ok. Two pots set the min and max voltages. Noted. Rk allows you to add current to the zener to get it past the most nonlinear portion of it's V-I curve. Understood. This circuit has the ability to calibrate out almost any component variation. That sounds like the sort of thing I was hoping to hear. ;-) It's relatively temperature independent. As long as it will cope with the -10 to +10 DegC range it should be fine here in the UK. ;-) You can use any meter that will make full scale at less than about 7V. And that's most small panel meters I'm sure. Downside is that the pots are vibration sensitive and subject to moisture/corrosion. Sure, but in my case they won't be subject to any real vibration and will be in a sealed enclosure. Also I would typically use a quality multiturn pot of the smallest value possible to give me sufficient 'trimming' around the end points and quality resistors to do the main bridge / work. Are we having fun yet? Well, it's certainly bringing some interesting and varied solutions out of the woodwork. ;-) It might also help me use up my stock of BC107's. ;-) Cheers, T i m |
#76
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Analogue moving coil meter range extension?
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#77
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Analogue moving coil meter range extension?
On 9/26/2017 7:49 PM, T i m wrote:
Too much information (variables) for me in most cases mate.;-) You keep missing it. Here it is again. The simplest is a 20K resistor in series with a 10v zener diode. Use a low current Zener so the knee works right at low values. Something like this: http://www.mouser.com/ds/2/395/BZX55C2V0%20SERIES_D1610-1099630.pdf Note, this is a DO-35 package. -- Jeff-1.0 wa6fwi http://www.foxsmercantile.com |
#78
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Analogue moving coil meter range extension?
On Wednesday, 27 September 2017 01:49:50 UTC+1, T i m wrote:
On Tue, 26 Sep 2017 15:29:19 -0700 (PDT), tabbypurr wrote: snip Yeah, ok ... but what about the question re using a lower value zener to get it away from the 'knee', especially as it's no more difficult to do? The zeners with the straightest knee are at 9-10v. Ok, so again that helps because I'd go for a 9V zener to get AFA I can from that 10V threshold and still retaining the sharpest knee. ;-) Go look at the linked data sheets. Too much information (variables) for me in most cases mate. ;-) Ah, you can use the 9V zener but it only comes in SM and you have to buy 1000. The 10V are easier to get but need a higher current ... etc etc. I don't play chess or poker or any game of chance for that matter (preferring FPS when I can shoot my fellow players in the face). ;-) The whole point to me of asking those who know is they are the ones who should all agree on a single 'best' solution. ;-) More than one way to skin a cat? (But for that as long as it does get skinned is good enough for me [1]). Cheers, T i m [1] I couldn't hurt one but I don't see the point in them ... apart from a source of whiskers for crystal sets and guts for violins. ;-) Just use a 10v zener. Job done. There's little point in the rest when the meter is so coarsely marked. You can adjust for 10v mechanically. You should find one in your scraps box. Catgut is made from sheep, goats etc. NT |
#79
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Analogue moving coil meter range extension?
On 9/26/2017 5:40 PM, T i m wrote:
On Tue, 26 Sep 2017 14:13:20 -0700, mike wrote: snip Yeah, ok ... but what about the question re using a lower value zener to get it away from the 'knee', especially as it's no more difficult to do? Since we're just trying to be clever, I'm not mike, I'm just trying to refine the design of any solution to be as good as possible with the fewest possible components. ;-) Try this: https://i.imgur.com/irLisN7.jpg The transistor and zener make a temperature compensated ~7V reference (must use 6.2V zener with standard tempco). Ok. Two pots set the min and max voltages. Noted. Rk allows you to add current to the zener to get it past the most nonlinear portion of it's V-I curve. Understood. This circuit has the ability to calibrate out almost any component variation. That sounds like the sort of thing I was hoping to hear. ;-) It's relatively temperature independent. As long as it will cope with the -10 to +10 DegC range it should be fine here in the UK. ;-) You can use any meter that will make full scale at less than about 7V. And that's most small panel meters I'm sure. Downside is that the pots are vibration sensitive and subject to moisture/corrosion. Sure, but in my case they won't be subject to any real vibration and will be in a sealed enclosure. Also I would typically use a quality multiturn pot of the smallest value possible to give me sufficient 'trimming' around the end points and quality resistors to do the main bridge / work. Use a small value pot with a fixed resistor on each end. Easier to set, more stable. Are we having fun yet? Well, it's certainly bringing some interesting and varied solutions out of the woodwork. ;-) It might also help me use up my stock of BC107's. ;-) Cheers, T i m |
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