DMM controls - Page 1
Forum section: electronics / testgear

author: spanakop
author_rank: Contributor
timestamp: April 27, 2021, 10:45:45 am
content: Given the added design overhead in coming up with a mechanical dial with decent feedback and robustness etc, along with the design of all of the PCB tracks, wouldn't it be simpler to have a bunch of buttons to select each function?Granted there would be a lot of buttons on the front, but it's surely better than having one rotary dial and you physically moving it around. The DER DE-5000 LCR meter and some Aneng meters are examples of where it works well. It seems odd in that we still have mechanical switches when we have decent electronic switches available that have been used for a long long time.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 27, 2021, 11:06:57 am
content: The rotary dial would last 30 years or more. I doubt the buttons would last that long.

author: Fungus
author_rank: Super Contributor
timestamp: April 27, 2021, 11:15:55 am
content: It's good having a big mechanical thing on the front that always points to the range in use.Quote from: spanakop on April 27, 2021, 10:45:45 amIt doesn't seem to be a problem in practice.Buttons have been tried lots of times. I don't think anybody found the right formula yet.Fluke even makes a meter with just two positions on the dial (well, three if you count "off" as a position).

author: Fungus
author_rank: Super Contributor
timestamp: April 27, 2021, 11:20:59 am
content: Quote from: BeBuLamar on April 27, 2021, 11:06:57 amThey could, but they wouldn't be simple rubber-dome buttons.They'd have to mechanical, so we're back to cost/complexity of mechanical things with good feedback, etc. The dial might start to look attractive compared to that.

author: HKJ
author_rank: Super Contributor
timestamp: April 27, 2021, 11:27:54 am
content: Quote from: spanakop on April 27, 2021, 10:45:45 amThey already exist, both in as cheap meters (Mostly automatic) and as expensive meters. They has one or more relays to handle the selection in addition to electronic switching.

author: spanakop
author_rank: Contributor
timestamp: April 27, 2021, 11:34:43 am
content: I have old 80's Casio calculators that are still good and most if not all modern DMM's also have buttons on the top row, so it is possible to have buttons perform functions that are expected to last the life of the device.True the cheaper auto DMM's and expesive units with relays do exist that have all buttons, but I still think designing and manufacturing a rotary dial function over buttons is still "complex". I can't see any reason other than it's traditionally done this way, to not start offering all button devices now.

author: joeqsmith
author_rank: Super Contributor
timestamp: April 27, 2021, 11:37:31 am
content: My bench DMMs use buttons exclusively. I bought a couple of very old Fluke 97 scope meters which also only have buttons.Many of the handheld DMMs I've looked at use buttons to select secondary functions. One uses a relay to perform the actual switching. You can change the state of the relay with a simple magnetic hanger. This can cause the meter to display very low voltages when high voltages are present. There are a few handheld DMMs I have seen using relays like this.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 27, 2021, 11:38:47 am
content: Quote from: Fungus on April 27, 2021, 11:15:55 amI have one of those. It's all I need most of the time. I don't really need to pull out my 87V or 289.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 27, 2021, 11:45:45 am
content: Quote from: spanakop on April 27, 2021, 11:34:43 amAlthough it's traditional for the analog VOM to have a dial it's not so for a DMM. In fact early Fluke DMM's only had buttons. But those buttons are not simpler nor cheaper than the dial they use now.

author: HKJ
author_rank: Super Contributor
timestamp: April 27, 2021, 11:46:12 am
content: Quote from: spanakop on April 27, 2021, 11:34:43 amNot really, the molds for the mechanic already exists, there is no need to design a new switch for each meter. If you look at the backside of a rotary switch you will often see extra slots for more sliders, i.e. the design can be used for more advanced switching without doing any changes to the molds.Anyway a typical rotary switch do not need to switch much:1) It need to signal the position to the DMM chip.2) It need to short the uA shunt and move the sense connection to before it when in mA.3) It need to switch the current generator onto the V/ohm/etc terminal when a range requires that.For more advanced meters it may also need to switch a capacitor in on VAC.Everything else can be done electronically and most of it is. I have seen 3) done electronically on a single cheap meter and 2) done electronically on some very expensive DMM's.

author: Fungus
author_rank: Super Contributor
timestamp: April 27, 2021, 11:46:47 am
content: Quote from: spanakop on April 27, 2021, 11:34:43 amMultimeters are often used in conditions that would kill a calculator in five minutes.

author: HKJ
author_rank: Super Contributor
timestamp: April 27, 2021, 12:05:38 pm
content: Here is a meter with all buttons:But there are two meters where the range switch is only a signal about selected range and do not switch any measurement voltages, with the two other meters the range switch will switch some measurement voltages.In usage I prefer the rotary switch.

author: Fungus
author_rank: Super Contributor
timestamp: April 27, 2021, 12:09:23 pm
content: Quote from: BeBuLamar on April 27, 2021, 11:38:47 amThe only problem I see with it is the input impedance - only about 3kOhms.That image must be old. The 113 on theFluke web siteis CAT IV 600V.

author: Fungus
author_rank: Super Contributor
timestamp: April 27, 2021, 12:13:29 pm
content: Quote from: HKJ on April 27, 2021, 12:05:38 pmHere's another one:

author: spanakop
author_rank: Contributor
timestamp: April 27, 2021, 12:16:59 pm
content: Quote from: Fungus on April 27, 2021, 11:46:47 amTrue, they wouldn't last very long, not even five seconds. But my point is that using these kinds of buttons can last a very long time. As I said, the top row of buttons are already on DMM's are there, why not expand it to the other functions.If you're going to design a hand held instrument to do the functions of a DMM, why would you even start with a rotary dial. And as joeqsmith mentioned, I missed the fact that bench DMM's are almost all buttons.

author: HKJ
author_rank: Super Contributor
timestamp: April 27, 2021, 12:23:26 pm
content: Quote from: Fungus on April 27, 2021, 12:13:29 pmThe switch handles all the switching required, i.e. switching the current generator to the V/ohm terminal and notifying the chip about the position.

author: HKJ
author_rank: Super Contributor
timestamp: April 27, 2021, 12:25:23 pm
content: Quote from: spanakop on April 27, 2021, 12:16:59 pmBench DMM's are filled with power hungry relays, you can't do that in a handheld DMM.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 27, 2021, 12:28:25 pm
content: Quote from: Fungus on April 27, 2021, 12:09:23 pmMost of the time the 3KOhms is OK. I wouldn't want to check 480VAC or 600+ VDC DC bus voltage on an inverter drive or servo drive though. Yes mine said CAT IV 600V. The 3K impedance is good for checking SSR output.

author: HKJ
author_rank: Super Contributor
timestamp: April 27, 2021, 12:32:49 pm
content: Quote from: BeBuLamar on April 27, 2021, 12:28:25 pmThe 3kOhm is only at low voltage, it will be much higher at mains voltage.Here is a curve from a Fluke 289:

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 27, 2021, 12:46:08 pm
content: I don't know but when I check 240V and 480V with it it causes a spark both with the 113 and the 289 in low Z.

author: HKJ
author_rank: Super Contributor
timestamp: April 27, 2021, 12:53:30 pm
content: Quote from: BeBuLamar on April 27, 2021, 12:46:08 pmWhen you connect the meter the resistance will be 3kOhm, but a fraction of a second later it will be much higher. It is a PTC where the resistance increases when it is heated. The steady state power will probably be around 1 Watt.

author: Cymaphore
author_rank: Regular Contributor
timestamp: April 27, 2021, 03:51:19 pm
content: My personal experience:It depends on where the device is in use.On a lab bench, it doesn't really matter so much.In "the field" it's a whole different story. When crawling arround in a dark cabinet, accidentially pressing one of those many buttons or pressing the wrong one can be a real showstopper.Rotary switches that can be single hand operated and that tell you about the selected range in a haptic way are superior in such an environment.So it depends on what you're doing and how you're doing it. Probably other people have good reasons for using those all-button meters (for example Metrix).

author: Cubdriver
author_rank: Unknown
timestamp: April 27, 2021, 04:35:32 pm
content: If you look at most modern meters, you'll see that the 'rotary switch' is mostly part of the main PCB. It has a carrier with contact(s), and the switch detents are molded into the case itself, with a plastic spring detent mechanism. Minimal parts count for a very functional switch that is both east to actuate and at the same time protected fairly well from accidental movement. It physically switches connections, and they then stay connected. The pushbuttons on the top row of such meters are momentary, and activate logic level functions - they don't/cant do switching like the purely mechanical rotary switch can - you'd need them to turn on/off internal circuits that could then do the switching, and likely with more loss than a purely mechanical contact that's just there, not to mention they'd draw power (not good in a handheld, battery powered device) while the mechanical switch's contacts are purely passive in that regard.If you look at the pushbuttons on bench meters, they're either logic level and drive power consuming components, or are mechanical, in which case they are likely considerably more complex than the simple rotary switch currently used. Look at the early Fluke handhelds that had the buttons along the left side - those are a mechanical nightmare compared to the low parts count rotary currently in use - they each consist of many components (individual contacts staked into a base, a slider, moving contacts in the slider, a spring to force the slider to its 'home' position, a mechanism to lock the slider in the desired location, for ganged switches some means to interconnect them to each other to disengage one when another is pushed.Look at these from a Fluke 8200 bench meter, for instance:Before even adding the keycaps and the stuff to hold them together and couple the mechanism, I can count AT LEAST 12 parts in EACH switch - from the front, the plunger, the spring retainer, the spring, the switch body, six fixed contacts and two moving ones. There may well be more, too - the plunger may fit into an internal carrier for the moving contacts, and they may be spring loaded themselves. It's a pretty complex little piece of hardware. now add six more of them and interconnect them to work properly in unison - more fun.In short, manufacturers largely stick with the rotary switch because it's simple and it works.-Pat

author: tooki
author_rank: Super Contributor
timestamp: April 28, 2021, 01:35:37 am
content: Quote from: HKJ on April 27, 2021, 12:25:23 pmMany handheld DMMs use relays. For example, the Keysight U1252B.

author: Black Phoenix
author_rank: Super Contributor
timestamp: April 28, 2021, 04:52:28 am
content: Quote from: Cubdriver on April 27, 2021, 04:35:32 pmBut you have to admit that a rotary switch may be simpler to implement and can be a joy to use when the parts don't have almost any play and are solid, but a good old school mechanical switch well maintained is "orgasm" for the fingers in terms of feeling.It's the same as rotary encoders, simple and work but a genuine Alps is a different beast.

author: Fungus
author_rank: Super Contributor
timestamp: April 28, 2021, 06:31:27 am
content: Quote from: tooki on April 28, 2021, 01:35:37 amYep. There's even some cheapo Anengs with relays inside them.

author: HKJ
author_rank: Super Contributor
timestamp: April 28, 2021, 07:08:39 am
content: Quote from: Fungus on April 28, 2021, 06:31:27 amThe cheap DMM's uses a single power hungry relay, the DMM's I posted before uses a few pulse controlled relays, that is a bit more tricky to control, but do not use any power in either position. Bench meters usually have more relays and will often use the power hungry version (344xxA series use 3 pulse controlled relays, DMM6500 uses 6, probably the power hungry type, same with East Tester ET3240, Siglent SDM3045X uses 5).It is possible to make handheld DMM's with buttons as can be seen on my photo above, but it is not the same as bench meters, they are designed differently. Using relays will usually increase power consumption and that is not something that is wanted in a good handheld DMM (But the cheap Chinese do not care). Gossen have succeeded in keeping the power consumption low, even with relays, but not everybody like their solution (See what Joe says about a Gossen meter).

author: shakalnokturn
author_rank: Super Contributor
timestamp: April 28, 2021, 07:22:29 am
content: Other than added complexity would there be a good reason not to use static relays?

author: HKJ
author_rank: Super Contributor
timestamp: April 28, 2021, 07:32:45 am
content: Quote from: shakalnokturn on April 28, 2021, 07:22:29 amThey are sensitive to high magnetic field, i.e. a hanger for a DMM may change the relay making the DMM show a wrong value.

author: 2N3055
author_rank: Super Contributor
timestamp: April 28, 2021, 07:33:20 am
content: Quote from: shakalnokturn on April 28, 2021, 07:22:29 amThey do. Metrix does, Gossen does.. That is why JoeQ could confuse them with permanent magnets...

author: HKJ
author_rank: Super Contributor
timestamp: April 28, 2021, 08:03:33 am
content: Quote from: 2N3055 on April 28, 2021, 07:33:20 amI have not seen Joe confuse a Chauvin Arnoux meter, they may be susceptible for magnetic interference or they may have added protection against it. There are two way to protect: Magnetic shielding or a position sense connection from the relay to the processor.The only guy I have ever heard about having problems with the relays is Joe, maybe because these meters are seldom used on a hanger.Note: Chauvin Arnoux is the brand behind Metrix and manufactures the meters.

author: spanakop
author_rank: Contributor
timestamp: April 28, 2021, 08:08:31 am
content: I Cymaphore has a good point here.Quote from: Cymaphore on April 27, 2021, 03:51:19 pmHowever, there are already protection mechanisms in place for accidentally activating or leaving a current measurement when you really want voltage for example (I have done this long a go, I wasn't paying attention, wasn't a pretty sight, lesson learn't there).There are many electronic devices that have moved away from mechanical designs or have been replaced by better designs altogether; cassettes, video players, spinny hardrives, radios etc off the top of my head. Even oscilloscopes. Gone is the CRT potentiometers, lever switches, now you have digital displays and rotary encoders. How many devices have a mechanical switch for powering on, a lot are simple push buttons now. I'm sure there are other examples.By removing the dial, you can also make it a little more compact, that dial and the supporting PCB tracks, take up a lot of room. That space could be taken up by a bigger display perhaps, more functions.I haven't got any objection to rotary dials, I do like the Brymen DMM's, I just think in this day and age they are not really needed anymore. It has been done already for some meters, I think they need to move forward and innovate a little more.

author: HKJ
author_rank: Super Contributor
timestamp: April 28, 2021, 08:37:22 am
content: Quote from: spanakop on April 28, 2021, 08:08:31 amIt is not always these changes are a advantage, like the soft power button that means the device uses power all the time, or a pushbutton that requires a lot of presses to select a value, instead of a rotary switch that can be directly turned to the desired position.Quote from: spanakop on April 28, 2021, 08:08:31 amLook at the photos I posted: The CA has space enough for a rotary dial and it has a very large display. The Gossen with a rotary dial is the most advanced meter of the four by a good margin.My guess on why CA uses buttons is because it can be fully computer controlled and then the switch would not match the actual function (Gossen have that issue).Quote from: spanakop on April 28, 2021, 08:08:31 amDials are a very effective way to select and adjust settings, often way superior to switches, using buttons may make a meter harder to use. I am using the CA as my main meter at the current time and I do not see the buttons as any advantage.

author: shakalnokturn
author_rank: Super Contributor
timestamp: April 28, 2021, 08:49:32 am
content: Quote from: 2N3055 on April 28, 2021, 07:33:20 amA bistable (mechanical) relay and static (semiconductor) relay are different devices.AFAIK bistable relays are used in some handheld DMM's.It will take a hell of a permanent magnet to confuse a static relay though...

author: HKJ
author_rank: Super Contributor
timestamp: April 28, 2021, 09:48:34 am
content: Quote from: shakalnokturn on April 28, 2021, 08:49:32 amI have never hard solid state relays called static before and they are not very static, they require a few mA to turn on and stay turned on, this will often double the power consumption on a DMM.The mosfets used to handle current shunts are not relays, they are not isolated and do not need any power to stay on.

author: 2N3055
author_rank: Super Contributor
timestamp: April 28, 2021, 10:06:36 am
content: Quote from: shakalnokturn on April 28, 2021, 08:49:32 amHehehe that is true..Sorry, I didn't understand you meant SSD by static relay..True, SSD is less power than bistable magnetic, but still some consumption..For slow changes, bistable magnetic average consumption converges to 0....

author: Cymaphore
author_rank: Regular Contributor
timestamp: April 28, 2021, 12:52:35 pm
content: If one works with electronics in a lab environment, magnetic interference, HRC-fuses and even shielding is in many cases not even a thing. Nice to have, but no problem. You probably care more about high resolution, precision and such things.If one works with synchronous motors and traction inverters, you usually prefer shielding and fuses over digit-count.It's all about the intended use case.That's why so many people out there are frequently complaining about HVAC and electrician meters (too few counts, AC comes first, missing duty cycle, etc., etc.). These are usually not "general purpose" meters, but rather focus on very specific use cases and take care of specific needs.Same with buttons vs. rotary switches. I don't think one of those solutions is generally better than the other. It depends on what it's used for and how it needs to be operated.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 28, 2021, 01:29:12 pm
content: Whenever I used the Fluke 287 or 289 I always turn it off when trying to turn on the back light. They put the power on/off button right where the backlight button is on the 87V. Also it takes me a second to realize that I have to turn it on with the button and not the dial.

author: David Hess
author_rank: Super Contributor
timestamp: April 29, 2021, 09:46:58 pm
content: A mechanical switching has advantages over electronic switching unless relays are used, and relays are expensive.