- Analogue moving coil meter range extension? - 19 Updates
- Does anyone have a schematic for Florida - 6 Updates
| T i m <news@spaced.me.uk>: Sep 21 06:51PM +0100 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? Once I have the 10V (that might need it's own drive resistor?) for the -ve side of the meter I think I'd need a 20k resistor in series with the meter to my 10-15V supply (a lead acid battery)? R = V/I = 5 / 250 x 10^-6 = 20k ohms. Or ... I could use a straight potential divider on the grounds that a moving coil meter isn't going to be that accurate in the first place? Maybe: -Ve, 10k, 5k, +Ve with 20k in series with the meter across the 5K? Am I close please? ;-) Cheers, T i m |
| "pfjw@aol.com" <pfjw@aol.com>: Sep 21 11:30AM -0700 There should be a way to rig a simple resistor to do what you need. You may have to re-scale the meter, but that should do it. Perhaps an adjustable wire-wound resistor that you could tweak until *your* voltage range matched the meter range? https://www.alliedelec.com/search/productview.aspx?SKU=70023692 As a one-off, the cost would not be too excessive. And the meter would be just as 'accurate' as before. But there should be no reason to get fancy. It would all depend on how much current is going through the resistor(s). Peter Wieck Melrose Park, PA |
| tabbypurr@gmail.com: Sep 21 12:05PM -0700 On Thursday, 21 September 2017 18:51:33 UTC+1, T i m wrote: > 5K? > Am I close please? ;-) > Cheers, T i m How accurate do you want the readings? Add your errors together. MC meters are usually pretty good on accuracy. NT |
| T i m <news@spaced.me.uk>: Sep 21 08:22PM +0100 On Thu, 21 Sep 2017 11:30:17 -0700 (PDT), "pfjw@aol.com" >There should be a way to rig a simple resistor to do what you need. I put forward 3 ways that were pretty simple. ;-) > You may have to re-scale the meter, but that should do it. I might adjust the scale reading from 1 to 5 to 10 to 15 but I didn't really want to do much more. > Perhaps an adjustable wire-wound resistor that you could tweak until *your* voltage range matched the meter range? The problem with any variable resistor is stability. I could be of for very fine tuning though. >https://www.alliedelec.com/search/productview.aspx?SKU=70023692 That's a bigun. ;-) >As a one-off, the cost would not be too excessive. Ok. Ironically the moving coil meter itself is more expensive than a digital display or even a wattmeter but I actually want to go old skool here. > And the meter would be just as 'accurate' as before. Ok. > But there should be no reason to get fancy. No, no reason maybe but if going a 'bit' fancy gives me a better solution and not for a lot of money or effort I don't mind going for it. ;-) >It would all depend on how much current is going through the resistor(s). Hopefully, no more than the 250uA required for FSD Peter. ;-) Cheers, T i m |
| T i m <news@spaced.me.uk>: Sep 21 08:24PM +0100 On Thu, 21 Sep 2017 12:05:59 -0700 (PDT), tabbypurr@gmail.com wrote: <snip> >How accurate do you want the readings? As accurate as the meter can be itself, ideally. >Add your errors together. MC meters are usually pretty good on accuracy. Ok, hopefully the biggest issue will be parallax error and my old eyes. ;-) Cheers, T i m |
| tabbypurr@gmail.com: Sep 21 12:35PM -0700 On Thursday, 21 September 2017 20:24:48 UTC+1, T i m wrote: > <snip> > >How accurate do you want the readings? > As accurate as the meter can be itself, ideally. Your total error is all the errors added together, so you'd need some exceptional circuitry to not add anything significant to the meter's error, which might be 1% or so. More realistic would be to keep the electronic errors within 1%. To get that you'd be using an opamp to knock 10v off, with 0.1% resistors everywhere it matters. Avoiding anything getting hot always helps keep the errors down, so anything that gets warm heatsink it, and operate parts way under their limits. Not that that will be a problem with this meter. NT |
| tabbypurr@gmail.com: Sep 21 12:37PM -0700 On Thursday, 21 September 2017 20:22:43 UTC+1, T i m wrote: > On Thu, 21 Sep 2017 11:30:17 -0700 (PDT), "pfjw@aol.com" > <pfjw@aol.com> wrote: > >There should be a way to rig a simple resistor to do what you need. there isn't > I might adjust the scale reading from 1 to 5 to 10 to 15 but I didn't > really want to do much more. > > Perhaps an adjustable wire-wound resistor that you could tweak until *your* voltage range matched the meter range? won't get you 10-15v range > digital display or even a wattmeter but I actually want to go old > skool here. > > And the meter would be just as 'accurate' as before. impossible > >It would all depend on how much current is going through the resistor(s). > Hopefully, no more than the 250uA required for FSD Peter. ;-) > Cheers, T i m :) Your opamp should do a nice job of protecting the meter, you just need to protect the opamp. NT |
| "pfjw@aol.com" <pfjw@aol.com>: Sep 21 01:18PM -0700 Like this? http://thumbs.ebaystatic.com/images/g/XAMAAOSw-0xYRaJT/s-l225.jpg Right off the shelf. Several others from similar sources with a table of resistance values to make the desired range (in volts) and either blank faces or sequential numeric faces. Sorry for pointing to an Euro-meter, but just that they are out there. Had I known, the "meter man" at Kutztown would have had exactly what you want in the size you want it, new or used. He has hundreds. Now you have to wait until spring. Peter Wieck Melrose Park, PA |
| "Ian Field" <gangprobing.alien1@virginmedia.com>: Sep 21 09:43PM +0100 "T i m" <news@spaced.me.uk> wrote in message news:vas7scdd02ptrj9igjpnhf4p46p35ehkfv@4ax.com... > 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? Most people just use a Zener and maybe a few normal (or SB) forward volt drops to trim the offset. I was thinking the TL431 programmable Zener could be calibrated to exactly what you need - but it needs a minimum current through it (possibly 1mA or so). You can probably incorporate a TL431 into some kind of bridge circuit with the movement spanning the 2 arms, but it will almost certainly need some kind of power supply. |
| T i m <news@spaced.me.uk>: Sep 21 09:44PM +0100 >> >How accurate do you want the readings? >> As accurate as the meter can be itself, ideally. >Your total error is all the errors added together, I know. >so you'd need some exceptional circuitry to not add anything significant to the meter's error, which might be 1% or so. More realistic would be to keep the electronic errors within 1%. Understood. >To get that you'd be using an opamp to knock 10v off, Why not a zener or precision voltage IC? >with 0.1% resistors everywhere it matters. As long as the final result calibrates correctly, does it matter what the tolerances are / were? >Avoiding anything getting hot always helps keep the errors down, With 250uA FSD I can't anything much getting warm? >so anything that gets warm heatsink it, and operate parts way under their limits. Not that that will be a problem with this meter. Quite. So, precision reference, zener, resistor bridge? With a precision reference and zener my meter wouldn't start doing anything till the measured voltage started to exceed 10V, even if I was ramping from 0 to 15V (and that's fine for a 12V lead acid). With a resistor bridge with a 1/3 split I should be able to get FSD at my 15V but anything less wouldn't work (would it?) ... so it's going to have to be either of the first two ... or something else? Basically, as long as I hold the negative of the meter at the same voltage as the positive at anything 10V and below, the meter won't do anything. Then as the +ve of the meter exceeds 10V and goes to 15V, a meter set to read 0-5 volts should follow ok, giving me reasonable / best possible accuracy across the working range of the battery. The only prerequisites are to ensure the -ve of the meter is held exactly at +10V (from a supply ranging from 10.5 to 14.4V) and that the meter current limiting resistor is correctly matched (to give the 250uA required for FSD at 5V PD). As long as any reference would be suitably driving at anything above 10V and not overdriven at 15V then we should be good to go? Cheers, T i m |
| T i m <news@spaced.me.uk>: Sep 21 09:51PM +0100 On Thu, 21 Sep 2017 21:43:31 +0100, "Ian Field" >> associated resistor(s) please? >Most people just use a Zener and maybe a few normal (or SB) forward volt >drops to trim the offset. Ok. >I was thinking the TL431 programmable Zener could be calibrated to exactly >what you need - but it needs a minimum current through it (possibly 1mA or >so). Well that's ok? >You can probably incorporate a TL431 into some kind of bridge circuit with >the movement spanning the 2 arms, but it will almost certainly need some >kind of power supply. Because the reference voltage will be too close to the minimum voltage expected Ian? If that is the case I could use a very light bang converter to bring the supply up to say 15 V and power it from the source that is being monitored in use (running an electric outboard from a 93Ah battery). Cheers, T i m |
| tabbypurr@gmail.com: Sep 21 02:37PM -0700 On Thursday, 21 September 2017 21:44:35 UTC+1, T i m wrote: > Understood. > >To get that you'd be using an opamp to knock 10v off, > Why not a zener or precision voltage IC? which one? > >with 0.1% resistors everywhere it matters. > As long as the final result calibrates correctly, does it matter what > the tolerances are / were? There are 2 ways to get accuracy. 1. adjust/calibrate 2. build it accurately I don't know which suits you better. Long ago I used to use selected 5% resistors where 1% were wanted, but they don't stay as accurate as 1%ers. > >Avoiding anything getting hot always helps keep the errors down, > With 250uA FSD I can't anything much getting warm? no :) > With a precision reference and zener my meter wouldn't start doing > anything till the measured voltage started to exceed 10V, even if I > was ramping from 0 to 15V (and that's fine for a 12V lead acid). If you had a perfect-knee perfectly accurate voltage zener then sure, but where will you find one of those? > With a resistor bridge with a 1/3 split I should be able to get FSD at > my 15V but anything less wouldn't work (would it?) ... so it's going > to have to be either of the first two ... or something else? or resistors on the input of an opamp so it only turns on once 10v is reached > As long as any reference would be suitably driving at anything above > 10V and not overdriven at 15V then we should be good to go? > Cheers, T i m There's always protection to consider. NT |
| Foxs Mercantile <jdangus@att.net>: Sep 21 04:54PM -0500 Sigh.... The simple answer is put a 62K 5% resistor in series with the meter. It's read about 4% low (240 uA instead of 250 uA.) You wanna get a little closer? put a 100K and a 150K in parallel. Wanna make it adjustable? Put a 100K trimpot in parallel with a 180K resistor. This ain't rocket science folks. -- Jeff-1.0 wa6fwi http://www.foxsmercantile.com |
| T i m <news@spaced.me.uk>: Sep 21 11:41PM +0100 On Thu, 21 Sep 2017 16:54:07 -0500, Foxs Mercantile <jdangus@att.net> wrote: >Sigh.... >The simple answer is put a 62K 5% resistor in series with the meter. >It's read about 4% low (240 uA instead of 250 uA.) Ok, so with our source at 15V we get 240 uA and ~FSD on our meter. That's 14.88V across the resistor and 0.12V across the meter, therefore the meter is ~500 ohms? At 10V we get 2/3 of 240 uA (160uA) and so our voltage across the meter is now 0.0256 (~1/5th of FSD) and so the meter will read 1 volt and not 0? >You wanna get a little closer? put a 100K and a 150K in parallel. >Wanna make it adjustable? Put a 100K trimpot in parallel with a 180K >resistor. The problem is that the voltage across the meter will fall in proportion to the voltage across the entire network, not just across the meter component (which is why I ruled it out in my second post). ;-) >This ain't rocket science folks. Maybe not but can appear as such to some (I think). ;-) Cheers, T i m |
| Foxs Mercantile <jdangus@att.net>: Sep 21 05:59PM -0500 On 9/21/2017 5:41 PM, T i m wrote: > Ok, so with our source at 15V we get 240 uA and ~FSD on our meter. > That's 14.88V across the resistor and 0.12V across the meter, > therefore the meter is ~500 ohms? No that's 15 volt across the resistor only so it's ~240 uA. With the internal meter resistance it would be slightly less current. > At 10V we get 2/3 of 240 uA (160uA) and so our voltage across the > meter is now 0.0256 (~1/5th of FSD) and so the meter will read 1 volt > and not 0? No, it's still assuming the meter resistance is close to zero. at 160 uA, it will read 2/3 scale at 10 volts. > The problem is that the voltage across the meter will fall in > proportion to the voltage across the entire network, not just across > the meter component (which is why I ruled it out in my second post). No, you're NOT measuring voltage across the meter. You're measuring current through the meter. It's a series circuit. (The meter and the series resistor.) As such in this case, the series resistance is much higher than the internal resistance of the meter, and that defines what the current will be for a given voltage. I.e. 60K ohm, 15 volts, 250 micro-amps. -- Jeff-1.0 wa6fwi http://www.foxsmercantile.com |
| Foxs Mercantile <jdangus@att.net>: Sep 21 06:11PM -0500 How things work: Amp meters, by definition are suppose to be low resistance items. When you're measuring current through a circuit, you don't want to waste any of the available voltage across the meter. As an example of this, current shunts for meters are usually rated at X-amps for 50-100 mV across the shunt. On the other hand, volt meters are put in parallel with a load, and to be accurate, they should be many time higher than the load resistance so they don't pull the supply voltage down that you're trying to measure. Back in the "good old days" for example, they would specify taking a voltage reading with a "minimum 20K ohms/volt" meter. If your trying to measure 100 volts, if you have a 150 volt range on the meter, this would be a load resistance of 3 megohms across the circuit you're measuring. In the example given for a 250 uA meter, that's only 4K/volt. But for measuring 10-15 volts, most supplies are good for anywhere from 1-25 amps, so the extra 250 uA is hardly noticeable. -- Jeff-1.0 wa6fwi http://www.foxsmercantile.com |
| tabbypurr@gmail.com: Sep 21 04:16PM -0700 On Thursday, 21 September 2017 22:54:17 UTC+1, Foxs Mercantile wrote: > Wanna make it adjustable? Put a 100K trimpot in parallel with a 180K > resistor. > This ain't rocket science folks. It's also plainly noncompliant with the project requirements. NT |
| T i m <news@spaced.me.uk>: Sep 22 12:23AM +0100 On Thu, 21 Sep 2017 14:37:35 -0700 (PDT), tabbypurr@gmail.com wrote: <snip> >> Why not a zener or precision voltage IC? >which one? That was my question. ;-) >> the tolerances are / were? >There are 2 ways to get accuracy. >1. adjust/calibrate But adjustability sometimes brings with it lower precision (noise). >2. build it accurately Ok. >I don't know which suits you better. Whatever works best on the day. ;-) >Long ago I used to use selected 5% resistors where 1% were wanted, but they don't stay as accurate as 1%ers. Ok. >> >Avoiding anything getting hot always helps keep the errors down, >> With 250uA FSD I can't anything much getting warm? >no :) ;-) >> anything till the measured voltage started to exceed 10V, even if I >> was ramping from 0 to 15V (and that's fine for a 12V lead acid). >If you had a perfect-knee perfectly accurate voltage zener then sure, but where will you find one of those? Pass, hence the questions. >> my 15V but anything less wouldn't work (would it?) ... so it's going >> to have to be either of the first two ... or something else? >or resistors on the input of an opamp so it only turns on once 10v is reached Ok, but you still need to hold the -Ve end of the meter *at* 10V as the source goes between 10 and 15V? A LM4040DIZ-10.0 works like a zener so that would probably do. If I've read the datasheet properly the (10V) device requires a minimum of 100uA and a maximum of 15mA. http://www.ti.com/lit/ds/symlink/lm4040-n-q1.pdf So, if we ignore the meter and assume a worst case battery voltage of 10.5V then we have .5V to get 100uA so that's 4k7 and giving us 1mA at 15V. We would also have 20500 ohms (20k series resistor and 500 ohms of the meter) in parallel with the chip feed to help ensure it stays over 100uA. >> 10V and not overdriven at 15V then we should be good to go? >> Cheers, T i m >There's always protection to consider. I think about all that would work (without affecting the accuracy / functionality) is a very small series fuse and reverse biased diode across the input to the meter circuit ? Cheers, T i m |
| T i m <news@spaced.me.uk>: Sep 22 12:35AM +0100 On Thu, 21 Sep 2017 18:11:32 -0500, Foxs Mercantile <jdangus@att.net> wrote: >In the example given for a 250 uA meter, that's only 4K/volt. >But for measuring 10-15 volts, most supplies are good for anywhere >from 1-25 amps, so the extra 250 uA is hardly noticeable. But still, ohms law applies and with just a series resistor to limit the current for FSD, zero on the meter (re-marked to display 10V) won't reflect the required 10V. For the meter to read zero there would have to be zero volts across it and with just your series resistor that would only happen when the supply voltage = zero. So, a simple series resistor won't work for a meter reading from 10 (not 0) to 15V (but I'll be happy for you to explain it otherwise). ;-) So, you need something to hold the -ve of the meter at 10V (and the +ve of the meter to supply via a ~20k resistor) to allow the meter to work in the range of 0 to 5V, marked to show 10 - 15V. I hope that makes the requirement clearer. ;-) Cheers, T i m |
| mogulah@hotmail.com: Sep 21 11:03AM -0700 On Thursday, September 21, 2017 at 8:24:07 AM UTC-4, Michael Terrell wrote: > > Well, except for Donald Trump. Nothing is too horrible for that fuckwit. > How many billions have you made? How many thousands of jobs have you > created? "Compared with average business performance in the real estate sector, Trump squandered billions of dollars over the course of his career." Huffington Post-Jun 22, 2016 -- http://www.huffingtonpost.com/dmitri-mehlhorn/does-deadbeat-donald-have-any-money_b_10596614.html |
| "Michael A. Terrell" <mike.terrell@earthlink.net>: Sep 21 03:45PM -0400 > On Thursday, September 21, 2017 at 8:24:07 AM UTC-4, Michael Terrell wrote: > That DT is a successful *NEW YORK* real-estate developer, deadbeat and thief, and got there by stiffing contractors, bullying suppliers and vendors does not make him a good human being (he is not), an apt politician (he is not) or a creative force for the good (he is not). > That he is a billionaire is not due to his vision and creativity (Warren Buffet/Bill Gates et.al.). You make him sound like what you'd like to be. -- Never piss off an Engineer! They don't get mad. They don't get even. They go for over unity! ;-) |
| "Michael A. Terrell" <mike.terrell@earthlink.net>: Sep 21 03:45PM -0400 > "Compared with average business performance in the real estate sector, Trump squandered billions of dollars over the course of his career." > Huffington Post-Jun 22, 2016 > -- http://www.huffingtonpost.com/dmitri-mehlhorn/does-deadbeat-donald-have-any-money_b_10596614.html What? No quotes from Onion.com? -- Never piss off an Engineer! They don't get mad. They don't get even. They go for over unity! ;-) |
| "pfjw@aol.com" <pfjw@aol.com>: Sep 21 01:08PM -0700 On Thursday, September 21, 2017 at 3:45:10 PM UTC-4, Michael Terrell wrote: > You make him sound like what you'd like to be. Let me count the ways: a) I am happily married to my first wife (nearly 36 years). b) We have no debt. c) We have two houses. d) We have two successful, well-adjusted, happily married kids. e) Who have produced four well-adjusted and happy grand children. f) We have sufficient, reliable, income to last us for the rest of our natural lives, and still leave some for the kids. All of which we earned ourselves. g) We have roughly three times our gross annual income in savings, TSAs and other instruments in addition to the income. h) We have our health, we travel quite a bit, and we enjoy our lives. i) The cats and dogs are also healthy - the cats are both more intelligent than the average Republican as well, and I have the T-Shirt to prove it. The dogs are simply better than the average Republican. j) I sleep well and peacefully. tRump has nothing I want, nothing I would aspire to wanting, and has done nothing that catches my imagination or admiration. Clearly he lives an unhappy, frightened and tiny little world as proven by his tweets, choice of language, bullying behavior and pathological fascination with "winning". I wonder when he last got a good night's sleep, or if he will get one ever again in the future. Peter Wieck Melrose Park, PA |
| Trevor Wilson <trevor@SPAMBLOCKrageaudio.com.au>: Sep 22 07:05AM +1000 On 21/09/2017 10:23 PM, Michael A. Terrell wrote: >> I take no joy in hearing about the suffering of other human beings. >> Well, except for Donald Trump. Nothing is too horrible for that fuckwit. > How many billions have you made? **Do you mean: How many millions did I inherit from my father? How much real estate have I bought and sold? How many lies have I told in order to scam people out of their money? How many thousands of jobs have you > created? ** I suspect you intended to ask: How many people have lost everything because I declared bankruptcy 4 times? Answer: I never have. I have paid every single cent to every creditor I've ever done business with. Trump is a world-class arsehole. He is a dodgy businessman, who inherited a huge fortune and parlayed that fortune into a larger fortune, by lying, cheating and stealing. -- Trevor Wilson www.rageaudio.com.au |
| Foxs Mercantile <jdangus@att.net>: Sep 21 04:17PM -0500 On 9/21/2017 4:05 PM, Trevor Wilson wrote: > Trump is a world-class arsehole. He is a dodgy businessman, who > inherited a huge fortune and parlayed that fortune into a larger > fortune, by lying, cheating and stealing. You're wasting your breath on this one. Michael has spent the entire 8 years of President Obama bitching about "That Nigger in the White House." And replaying all the usual claptrap from the Right Wing echo chamber. Trivia, he's a mulatto, not a nigger. They couldn't even get THAT right. -- Jeff-1.0 wa6fwi http://www.foxsmercantile.com |
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