Where to buy a D'Arsonval movement? - Page 1
Forum section: electronics / projects

author: SpannersToSparks
author_rank: Regular Contributor
timestamp: April 21, 2017, 11:13:34 pm
content: HiI am doing The Art of Electronics Student Manual Course. Ive spent a few hundred and a good chunk of time on the published parts list, got a lab set up with oscilloscope, FG, multimeter, oscilliscope ... just sat down to get my teeth into it and...In the very first lab, he invites you to make your own voltmeter / ammeter (cool!)... using a part that he didn't list in the parts list (booooo).After some digging, it seems the part I need is a "D'Arsonval movement", just the bare naked mechanical movement found inside analog ammeters and voltmeters. Where do you buy these things from? Ebay, amazon, the web all returned a blank.Can I just buy a cheap analog voltmeter like this one and extract its mechanism?https://www.amazon.co.uk/d/DIY-Tools/SODIAL-0-300V-Round-Analog-Voltmeter/B00HPKCW7C/ref=pd_day0_60_8?_encoding=UTF8&psc=1&refRID=BM8492E9HTJG3G8EX3V6EDIT: Bit of an update. I have managed to find two companies that make them, one in Taiwan called Herrong, and one in the US called Hoyt meter. However neither seem to have an easy means of buying just a one off unit and sending to the UK.http://hoytmeter.com/product/meter-movements/http://www.herrong.com/KH.htm

author: edpalmer42
author_rank: Super Contributor
timestamp: April 22, 2017, 03:15:40 am
content: I don't know exactly what's in the Student Manual, but I think you've veered a bit off course.Don't look for a D'Arsonval movement, just look for an analog meter. Does the manual say anything about what the sensitivity should be? If so, look for an analog meter that's similar. e.g. "50 ua full scale" or "1 ma full scale". Check your favorite 'cheap analog multimeter' store and see what the most sensitive DC current range is. It will probably work just fine.Ed

author: vk6zgo
author_rank: Super Contributor
timestamp: April 22, 2017, 03:33:04 am
content: No,you don't need the naked , unprotected "guts".Such meter movements come enclosed in a panel mount, & are called "moving coil" milliammeters or microammeters, depending upon their full scale deflection (FSD).Nobody calls them "D'Arsonval" any more-----except Uni labs, & possibly, in India.Common FSDs are 1mA (older types usually), 500uA, 100uA , & 50 uA.You can still buy them "over the counter" in Oz at Jaycar, at $A 17.95.Emboldened, I looked at Maplins in the UK.Their answer was "Duhh! not found".RS Components in the UK do have them "over the counter", But, hold onto your hat!They are about 15.00 pounds sterling!!I would suggest that you look out for "Hamfests" , (or as they are more commonly called in the UK, "Radio Rallies") in your area.You may be able to pick up a meter for a couple of quid.( the older 1mA ones are likely to be the more common).

author: vk6zgo
author_rank: Super Contributor
timestamp: April 22, 2017, 04:34:06 am
content: You do realise that you don't really have to make a physical voltmeter/ammeter from scratch, don't you?The majority of people that I know in the Electronics field learnt the theory, looked at some diagrams, perhaps "tore down" an existing meter, "called it good", & went on with their lives.There is only just so much fun you can have sticking a resistor in series with a meter!Ammeters are more fun,with their low resistance "shunts", but even with them, most of it is in the Maths."The Art of Electronics " was probably first written when most Electronics geeks had a couple of moving coil meter movements lying around in their "junk box".During WW2 these things were made in their millions, so many "War Surplus" ones (mainly 1mA FSD) were hanging around for years.Sadly, many have now gone to Landfill!.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 22, 2017, 05:00:04 am
content: Quote from: vk6zgo on April 22, 2017, 03:33:04 amD'Arsonval is the technical or scientifical term for it, credit to the first inventor. it has nothing to do with India. moving coil is just laymen term to it. people are less interested in building it because its more mechanical skill rather than electrical skill i guess, more like trying to build an electromagnetic motor from scratch, hell who call them "electromagnetic" motor anymore? people know them as brushed, BLDC, steppers etc. also just like semiconductors that we loved to use. there are field and people who are interested in learning on how to build them from raw sand.

author: mtdoc
author_rank: Super Contributor
timestamp: April 22, 2017, 05:00:19 am
content: As I posted in reply to the OP's concerns in the "Learning the Art of Electronics" thread - I think they are misreading those early pages in the book which are directed at a classroom environment with an ammeter movement already ready to go. After all LTAOE is was written to accompany a University lab course. I don't believe it was meant for the home user to have to go find one.In any case that part is not critical.But if someone wants to experiment with analog panel ammeters,they're very cheap on eBay

author: SpannersToSparks
author_rank: Regular Contributor
timestamp: April 22, 2017, 10:39:53 am
content: So for clarirication, here is the text from the 2016, recent print version of the book:"An analog multimeter or VOM is just such a movement, with switchable resistor networks attached. We would now like you to reinvent the multimeter". Not USE a multimeter. He then presents a diagram of the mechanism - not a multimeter. For added clarification on whether he wants you to use the multimeter, or the naked mechanism, he adds:"Please note: We want you to work with a simplebare meter movement, not with a multimeter. (Its more fun that way)."The experiment isnotcalling for you to play around with an off the shelf analog meter. As to its utility - I want to do it. This is not a uni course, or a work course. Its a "doing it for myself because I want to" course.Thanks for the input.

author: Kilrah
author_rank: Unknown
timestamp: April 22, 2017, 12:02:37 pm
content: The best source for a needle movement is probably to take an old junk analog meter and remove all the resistor networks and switches.You can then pretend you never had a meter but just the movement, characterize it, calculate all the components you need to make it measure what you want, and with a bit of luck it happens you should have a lot of them handy to build your own meter since you just removed them.Indeed the course example kinda makes no more sense in this day and age. Back then it was super cool to be able to take junk parts and build yourself a useful device that you'd be able to use for the rest of your training and that would otherwise be somewhat expensive... but nowadays the source for the parts you need IS the very device you'd be building and it basically comes for free.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 22, 2017, 12:24:04 pm
content: Understanding how a D'Arsonval meter "motor" works, and even tearing one down, is one thing. Actually constructing one from scratch is essentially watchmaking (the old mechanical style). It seems hardly practical, especially here in the 21st century, to expect to make a functional D'Arsonval meter movement.Now, if you want to play around with a compass and a coil of wire, that will illustrate the basic principle.

author: Ian.M
author_rank: Super Contributor
timestamp: April 22, 2017, 12:31:10 pm
content: If you do a lot of OPAMP work, there's a certain utility in having a 50uA-0-50uA center zero panel meter, in a box with a switchable selection of series resistors and shunts to implement various FSDs up to say +/-10V and +/-10mA.However, other than opening such a panel meter to carefully replace the scale with one that is marked 20-0-20, 50-0-50 and 100-0-100 *WITHOUT* even touching *ANY* other part of the mechanism, there is absolutely *NO* point in screwing around with a bare, uncased D'Arsonval movement - they are just too fragile and difficult to adjust for anyone who isn't a miniature watchmaker to work on with good odds of success. I've done a bit of light meter fixing back in the day - straightening bent pointers, rebalancing movements etc. and the results were always a total toss-up. If you made contact with the hairsprings, you'd have to readjust zero and recalibrate FSD. The slightest bit of dust could result in stiction and a meter you had to tap for every reading. Then there was static electricity - something as simple as cleaning the scale or cover glass could leave a charge behind that attracted the pointer and resulted in errors that if you attempted to adjust them out, would leave you with large opposite errors after the charge leaked away.

author: max_torque
author_rank: Super Contributor
timestamp: April 22, 2017, 12:39:09 pm
content: Quote from: Richard Crowley on April 22, 2017, 12:24:04 pm^^ this, or an old bottle cork, two needles, and a length of copper wire:OK, that's a 'motor' but the effect is the same, as all you are demonstrating is that driving a current through a wire running perpendicular to a magnetic field generates a MMF.......

author: Rerouter
author_rank: Super Contributor
timestamp: April 22, 2017, 01:25:21 pm
content: Quote from: Ian.M on April 22, 2017, 12:31:10 pmI think your over-selling it a little, though i will admit part of my day job is calibrating and balancing these things to a linearity better than 0.5%Dust, and more likely metallic dust will be your biggest issue on older movements, you really need to have it clean before you begin anything else.If the pointer is bent or at the wrong height now is the time to fix it.next up you balance it at 2 deflection points, generally 1/3 and 2/3 for a 270 degree movement, this is more for cross checking yourself as your test tilts may be biased on an axis, you treat it like a helicopter blade, your corrections are 90 degrees away from the axis your tilting on,almost done, next is the scale, this is primarily the hairspring tension, if he isn't bent, you just need to pick 2 or 3 points on the movement that are even divisions, and adjust the tension until it deflects an even amount each time, even if the numbers are not there correct value.and finally is the zero. it may not be the mechanical zero, most movements will have a tiny bit of excess force at 0 to hold it against the stop, the first 2% of travel may be hidden, your balance may change slightly by adjusting the pointer, but in general its within the noise, as a meter should be better than 1% on the zero when the span is set correctly for a half decent movement.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 22, 2017, 02:04:46 pm
content: Quote from: max_torque on April 22, 2017, 12:39:09 pmadd control spring to the motor you get the D'Arsonval meter.http://www.engineersedge.com/instrumentation/electrical_meters_measurement/darsonval_movement.htmbuilding it is easy without watchmaking tools as long you are willing to make 10X mockup of what a factory can do. building motor or 8080 computer is much harder but... people eventually did it in this agefor education purpose ok, i have no objection.

author: Ian.M
author_rank: Super Contributor
timestamp: April 22, 2017, 02:41:12 pm
content: It might be interesting to build a Kelvinmirror galvanometer. It's a moving magnet design using a torsion fibre suspension, so no precision pivots or hair springs are required.If you use a strand of Kevlar for the fibre and two modern small thin Neodymium magnets sandwiching the fiber and a paper damping vane, and use aHelmholtz coilto apply the deflection current, so you can use the plated magnet pole end as the mirror, shining a laser pointer in from the side of the coil, it should be reasonable to build.

author: mikerj
author_rank: Super Contributor
timestamp: April 22, 2017, 03:37:50 pm
content: Quote from: SpannersToSparks on April 22, 2017, 10:39:53 amThat'sEXACTLYwhat it's asking you to do, I fear you have misunderstood the question. H&H says a multimeter is a bare movement with a switchable resistor network, and want you to reinvent the multimeter using the same kind of bare meter movement. Just for emphasis they stress that it has to be a meter movement and not a multimeter.I seriously doubt they would expecting you to source just the guts of a moving coil meter mechanism and to mount it yourself etc. that would be ridiculous and more like precision mechanical engineering than electronic engineering. Get the biggest 50uA panel meter you can find since you'll be needing to put a custom scales on it if you want to measure resistance etc.

author: SpannersToSparks
author_rank: Regular Contributor
timestamp: April 22, 2017, 04:09:04 pm
content: Quote from: mikerj on April 22, 2017, 03:37:50 pmIt does not read that way to me, but thanks for your interpretation. I had already emailed the author on a related issue and fielded that question, so hopefully he can confirm.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 22, 2017, 04:10:59 pm
content: Re: "Meter Movement"It appears that the objective here is to learn how to design a circuit that allows one to measure Voltage, Current, and Resistance over several ranges with nothing but a power source and a few resistors and a simple meter. The exercise teaches how a VOM multi-meter (whether digital or analog) works. And it gives you the understanding how to measure and scale various electrical properties.For example, if you were making a bench power supply, you would understand the principles of using a shunt to measure current. Doesn't matter whether you are displaying the current on a vintage D'Arsonval panel meter, or feeding an Analog to Digital converter input.When the book says "bare meter movement" it means a simple analog panel meter. It does not mean the very fragile and delicate D'Arsonval motor mechanism INSIDE the case. Unless you intend to become an "electronic archaeologist" and repair the antique things it is sufficient to understand that the meter needle moves relative to the amount of current through the coil.If I were doing this experiment, I would get something like: 50UA DC PANEL METER - CAT# PMD-50UA$12.00 each"http://www.allelectronics.com/item/pmd-50ua/50ua-dc-panel-meter/1.htmlUsing a meter that already has all the Volt, Amp, Ohms scales printed on it (as that Ebay Simpson replacement) is "cheating" as it has already worked out the non-linear resistance scale, etc. The objective of the exercise appears to be working out the circuit configuration, resistance/shunt values, and creating your own scales, especially for resistance.

author: SpannersToSparks
author_rank: Regular Contributor
timestamp: April 22, 2017, 04:26:05 pm
content: Hi RichardHave replied to you in other thread, thanks again for the help, I will go down this path with the 50uA panel meter.

author: mtdoc
author_rank: Super Contributor
timestamp: April 22, 2017, 05:18:21 pm
content: Yes, I'm afraid you've misunderstood the intent of the author. The word "invent" was not meant to be taken literally.This is just the beginning of the book! That section is just meant to get you thinking about Ohm's law and the relationship between current and voltage in a practical example while simultaneously demystifying analog meter movements.If you look at the bottom of that page, there is a note toinstructorsabout being sure to place diodes to protect the meters. So clearly, the meters were to be supplied by instructors in a classroom environment.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 22, 2017, 05:27:15 pm
content: Yes. You might want to get two or three meters. Especially the very sensitive low uA meters are quite vulnerable to catastrophic damage.Multi-meters (analog or digital) are typically internally protected from most abuse, but a "raw" meter movement should be protected by back-to-back diodes when experimenting in an open circuit.