How do you integrate an analog voltmeter and ammeter in one package? - Page 1
Forum section: electronics / projects

author: bjcuizon
author_rank: Frequent Contributor
timestamp: July 23, 2017, 05:37:16 am
content: Hi, I was curious how you would put an analog ammeter and a voltmeter together in a single package like one of those analog meters on an old bench power supply where you can toggle between amps or volts with a switch.Like this:If anyone has a schematic, that would really help.I am also planning to put it on a DIY Power supply of mine.Thanks.

author: BravoV
author_rank: Super Contributor
timestamp: July 23, 2017, 05:59:20 am
content: I did post a fully stitched HP 6114/6115A schematic at other thread ->HP Models 6114A and 6115A Schematic Diagram ColoredNot sure if your HP 6111A has exact schematic though, but HP 6114/6115A has the same feature which serves the same functionalities.

author: Unknown
author_rank: Unknown
timestamp: July 23, 2017, 06:05:48 am
content: In voltage mode the switch has the panel meter in series with a high value resistor; the small amount of current flow through the resistor and meter is used to indicate on the voltage scale.In current mode, the switch is just changing the panel meter to be in parallel with a current shunt, a low value resistor which the current of the power supply output flows through. The shunt takes most of the current due to its low resistance, and the coil of the meter takes a small amount of current, which is used to indicate on the amp scale. The resistance of the current shunt is chosen in combination with the resistance and sensitivity of the meter such that the scale works out properly.

author: daqq
author_rank: Super Contributor
timestamp: July 23, 2017, 07:29:49 am
content: Nothing magical really - the meter is just a simple electromechanical system. They generally have a 0-60mV (or +/- 60mV) or so voltage input. That translates to how much the needle moves from its center position.You can translate any kind of signal into the 60mV range with proper electronics. For voltage, it's just a resistive divider, for current it's a shunt resistor. Depending on the measured quantity (and range) you draw the scale on the meter, which can have several scales.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 23, 2017, 05:28:40 pm
content: this.. no need switch you see them all in one go...http://www.ebay.com.my/itm/DC-Combo-Meter-12V-24V-36V-48V-60V-72V-Car-Battery-Voltage-Current-Power-Monitor-/192112841143?var=&hash=item2cbad151b7:m:mS_b9zui8fMxoo-3l_EWh5g

author: bjcuizon
author_rank: Frequent Contributor
timestamp: July 25, 2017, 04:55:33 am
content: Yeah, but I want that old retro analog look on it.None of this digital displayrubbishstuff.

author: TimFox
author_rank: Super Contributor
timestamp: July 26, 2017, 08:49:24 pm
content: Usually, the actual panel meter is characterized by its full-scale current (1 mA or 100 uA is typical) and a (small but important) internal resistance. You can use "multiplier" resistors (as above) to make that a voltage meter, and put a voltage meter across a shunt resistor for current readings. Also, you can switch both sides of the meter with a double-pole switch for flexible circuitry (as opposed to usual digital panel meters that have a common connection).

author: Vtile
author_rank: Super Contributor
timestamp: July 26, 2017, 09:00:19 pm
content: You can also buffer the meter movement (google the most common type: d'arsonval meter movement) with tubes, transistors or ICs like OPAs.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 29, 2017, 10:46:18 am
content: Quote from: bjcuizon on July 25, 2017, 04:55:33 amstrange. there are many people in this world love to keep old retro stuff, i mean real old, like d'arsonval meter, round display CRO, tubes etc, they even stack tons of those on their drawer in front of the bench, for what? only the cow knows... and then there is also another type of people, they love modern stuff like color tft or 20x4 lcd with encoder and switch with 100 level of menu in firmware, this type of people are also many. but then when i posted my stuff with a little bit of digital display and a little bit of analog trimpot adjustment, nobody got interested, i guess i'm the last standing man of my type...

author: bd139
author_rank: Super Contributor
timestamp: July 29, 2017, 11:07:38 am
content: I'm with you. Trimpots, analogue, TTL, nothing newer. There isn't a single CPU on my bench

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 29, 2017, 11:09:56 am
content: except mine has a cpuits a strange blend between retro and modern

author: bd139
author_rank: Super Contributor
timestamp: July 29, 2017, 11:13:05 am
content: I've just realised my HP 5315A has a CPU in it so I was wrong anyway

author: Rerouter
author_rank: Super Contributor
timestamp: July 29, 2017, 02:29:45 pm
content: full scale current of the meter movement, for current, you place it in parallel with the shunt (parallel resistor math, you scale the shunt so at your full scale the meter gets its full scale current) and for voltage, with a series resistor inline to limit the full scale current to reflect your full scale voltage.As for interfaces, if its something that you want to tweak on the fly, i prefer knobs / potentiometers, if its something i need to be specific, generally a UI of some kind be it button or encoder.

author: cdev
author_rank: Super Contributor
timestamp: July 29, 2017, 04:39:36 pm
content: (I'm sorry, I didnt read your original post so closely and wrote all this under the assumption you were a beginner starting out.. but its long and might help somebody so I will leave it)On an electronics bench supply, specifically, its very nice to have a number of things - one of which is dual meters, whatever their type, analog or digital doesn't matter so much for everyday work, so you can see both current and voltage at the same time. Almost all bench supplies will give you either dual meters or the ability to switch between voltage and current.Not so frequently but enough times for it to be important, Ive had it happen that some device starts drawing an unusual amount of current and if you are used to what it usually draws when it suddenly starts drawing more you will notice, if your power supply meter shows it to you.Its even better to have both dual meters and whats called "constant current" adjustment on a supply, which lets you limit the short circuit current drawn by some experimental device to a little bit more than what its supposed to draw. Then the chance is much lower that it could self destruct.Otherwise, you may not notice it getting hot until something starts smoking or smelling funny and by them its usually too late.With constant current you can fix a broken device without fear of causing more damage by applying power by setting the constant current first.Then not only will you prevent any shorts from causing more damage, you can then instead track them down by a process of elimination and fix them.Thats why a good bench supply is worth every penny you spend on it.Actually, right now there are some great deals on fairly modern GW Instek (one example is the GPC-3020 triple supply) bench supplies on ebay, they cost a fraction of what anything of similar quality would cost you new, and although there are better deals on old equipment you need to do a lot more research and know what you are getting, and with these particular supplies the risk is virtually zero of getting a bad unit, because many of them are literally brand new or close to it.If you don't already have all the expensive parts in your parts box to build a decent bench supply you might want to consider getting one of them. For around $50-60 you can get a supply that you can probably use for decades, that would cost you at least $150 new.You should still build your own, especially if you have some need (high current or high voltage or high precision) and or already have the parts, its fun and a good way to save money, but in practical terms if you are a beginner trying to set up a bench you would likely end up getting a decent bench supply a bit down the line anyway, and now as there still are these used but still quite current units on ebay for a fraction of what they usually cost, and they are a known quantity, (known to be good) I would consider a GPC-3020

author: bjcuizon
author_rank: Frequent Contributor
timestamp: July 29, 2017, 10:00:25 pm
content: Quote from: Mechatrommer on July 29, 2017, 10:46:18 amSorry Mechatrommer, I didn't mean I did not like your idea. I just wanted a bit of old school on my PSU... Anyway, I don't have these really ancient test gear on my bench (you know, the type of gear where no one knows when it was built) and those multi-hundred vaccum tube pile. Hehe...But I also love a bit of digital things as well. My fun gen is DDS anyway. - just to say.