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Old 24th Mar 2017, 8:02 am   #1
stevehertz
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Default The swing of a needle vs accuracy and direct readout

I have my trusty AVO 8 and I also have a DVM (bought from Tandy, but works well). The latter provides accurate readings due to its high impedance and direct read out. However, when trying to view/measure a moving (say) voltage it is a right pain to understand what is going on, the LCD readout flickers all over the place. My question is, is there available a DVM that (somehow) has managed to combine the two aspects that I mention, ie accuracy and direct readout combined with something that shows 'trend' or movement? Maybe an instrument that has a traditional needle and a LCD display?
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Old 24th Mar 2017, 8:16 am   #2
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Default Re: The swing of a needle vs accuracy and direct readout

As far as combined LCD display and an analogue display i think they exist (or existed) but i can't remember the last time i saw one.

I too have a micronta/tandy/radio shack DMM. It is still great on the resistance range (albeit high resistances take a few seconds of sampling to reach a proper reading) but DCV are non-linear, and ACV have always been low (since day one.) Interestingly it does have trim pots inside but i have never touched them, as i think calibration at a given reference point would then initiate poor readings elsewhere.
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Old 24th Mar 2017, 8:22 am   #3
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Default Re: The swing of a needle vs accuracy and direct readout

Some DMMs include an analogue 'thermometer' readout in addition to the digits. However that is less responsive than an analogue meter and lacks the angular indication of a pointer.

No doubt for some obscure evolutionary reason, human perception is very sensitive to an angular readout. Hence we rely on it for most clocks & watches and car dashboard instruments. A quick glance is all that's required - no actual reading of numbers is involved.

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Old 24th Mar 2017, 9:01 am   #4
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Default Re: The swing of a needle vs accuracy and direct readout

As Martin said, quite a lot of up-market digital meters had bar-graph readout added to their display. It was a relatively cheap thing for manufacturers to add. Some of the posher ones even had it curved into an arc to give more of the feel of a moving pointer display. But they were used as a selling point and the makers could pump up the prices making a very significant boost to the profit

Users ultimately found them disappointing. There was rarely enough resolution to be useful, and there was usually a frustrating delay. Also, it moved around in jumps each time the digital display was updated because it was that data just displayed differently. Real time it was not.

So users never bothered looking at the things and soon sussed out they weren't worth any extra money.

I have several digital meters and I can't even tell you which ones have bar-graphs, but I can tell you where both my AVO 8s are, and the meter on my bench at home is an AVO EA113.

Most often, I measure voltage with an oscilloscope. That is very fast and immediate. It isn't very accurate, but that's OK most of the time. If I need anything more accurate, a meter gets used and I have a couple of standards lab grade 5 and 6 digit DMMs which only see very infrequent use.

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Old 24th Mar 2017, 9:28 am   #5
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Default Re: The swing of a needle vs accuracy and direct readout

I too prefer the "angular readout" of the analogue meter. In servicing (as opposed to laboratory) use, you very rarely need particularly high accuracy, you don't always even need to wait for the needle to come to a stop to see all you need.

For me, the needle position (or a CRT trace) gives a better mental image of what's going on in a circuit than a row of numbers, particularly if the row of numbers was auto-ranging. I have a few analogue meters with a centre zero setting (including the readily available Pro'sKit MT-2017) which are very useful for understanding what's going on in circuits with dual polarity power rails.

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Old 24th Mar 2017, 11:18 am   #6
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Default Re: The swing of a needle vs accuracy and direct readout

I have to agree with the views so far, particularly - and certainly in the case of most vintage stuff - you don't actually need 'Nth degree' accuracy levels. The old fashioned 'swing of a needle' tells the engineer much more than somewhat 'staid' numerical readout. I think I'll stick with what I've got and use each of them as best appropriate at the time.
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Old 24th Mar 2017, 9:42 pm   #7
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Default Re: The swing of a needle vs accuracy and direct readout

I had a couple of fluke 8600 bench DMM's, with both a 3.5 digit led readout, and a small analogue moving coil meter next to the display.

They are military spec (USA) and the moving coil meter is only really useful for seeing relative voltages, such as peaking a circuit.

The meter FSD was auto-ranged with the digital display.

It also doubled as a battery indicator by pressing a small button.

Also some bench DMM's have an analogue output on the rear which gives a voltage relative to the display value (not the DMM range), which can be hooked up to an analogue meter for a better visual display.

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Old 24th Mar 2017, 11:52 pm   #8
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Default Re: The swing of a needle vs accuracy and direct readout

I rather like the bargraph on my Fluke 89; I guess you get used to a particular bit of kit; nice large display digits, and large 'thick' bargraph.
Pictured with my old Beckman, hooked-up to my even older Farnell bench supply.

I think it was one of the Fluke 87 versions (old one?) that just had a 'cursor' that rides along the bottom of the screen - useless !
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Old 25th Mar 2017, 12:34 am   #9
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Default Re: The swing of a needle vs accuracy and direct readout

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Originally Posted by stevehertz View Post
My question is, is there available a DVM that (somehow) has managed to combine the two aspects that I mention, ie accuracy and direct readout combined with something that shows 'trend' or movement? Maybe an instrument that has a traditional needle and a LCD display?
With a modern bench meter you can always couple up a PC to it (eg via GPIB) and create the equivalent of an analogue movement in graphics. Some meters are quite fast in terms of readings/second and you could make a PC display that shows a needle and a realtime graph of the trend and also log the results to a file.
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Old 25th Mar 2017, 12:59 am   #10
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Default Re: The swing of a needle vs accuracy and direct readout

I've never found the Fluke cursor display particularly beneficial, either.

A cheap meter with a needle, for adjusting for a maximum or minimum, is brilliant. If you want to know what that peak actually is, you need accuracy, but that's when the DMM scores.

Like Radio Wrangler and stuarth, I also find an oscilloscope excellent for adjusting for a peak or trough. Although it's clearly a sledgehammer/ nut situation, the 'scope is such a useful piece of kit that it's always there and available!

A magic eye valve of course is also super for adjusting for max or min voltage, and response is super-fast, plus it's virtually immune from damage by a signal overload. Only down side is that these days they're a limited resource!
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Old 25th Mar 2017, 10:06 am   #11
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Default Re: The swing of a needle vs accuracy and direct readout

Quote:
Originally Posted by The Philpott View Post
I too have a micronta/tandy/radio shack DMM. It is still great on the resistance range (albeit high resistances take a few seconds of sampling to reach a proper reading) but DCV are non-linear, and ACV have always been low (since day one.) .
I have a cheap digital multimeter and on checking found that the impedance on AC was far less than that on DC so there would be a tendency to read low.

The, more expensive, Fluke meter I have got appears identical (and much higher) on both AC and DC.

I think 'horses for courses' and tend to use analogue meters for current measurements as I like to get a feel of the rate of change of current, and digital for voltage (as this is what I am usually varying manually as in valve tests etc).
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Old 25th Mar 2017, 10:07 am   #12
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Default Re: The swing of a needle vs accuracy and direct readout

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Originally Posted by stevehertz View Post
Maybe an instrument that has a traditional needle and a LCD display?
You mean like this?
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Old 25th Mar 2017, 10:50 am   #13
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Default Re: The swing of a needle vs accuracy and direct readout

That's the sort of thing i had seen (pictures of.)

Provided the internals are electrically sound (and calibrated) i suppose there's an element of double redundancy! I can well imagine the design going out of favour due to customers moaning that the displays read slightly differently from each other.
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Old 25th Mar 2017, 11:47 am   #14
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Default Re: The swing of a needle vs accuracy and direct readout

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You mean like this?
Thanks for that. It seems that Metrix make/have made quite a few MMs with analogue and digital functions. Does anyone have anything to say about their products? I've been on their web site.
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Old 25th Mar 2017, 11:58 am   #15
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Default Re: The swing of a needle vs accuracy and direct readout

Metrix are part of ITT.

I have one of their RMS DMMs but the LCD has gone bad and can only be read at an extreme oblique angle. It got frozen in the car every winter. Nothing to lose by opening it, I suppose.

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Old 25th Mar 2017, 1:44 pm   #16
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Default Re: The swing of a needle vs accuracy and direct readout

Agreed, it's "horses for courses". When my son's phone stopped working but his internet still worked, I checked the voltage on the incoming AB lines with everything unplugged and instead of about 50VDC was rewarded with sharp kick to about 5V followed by a decay consistent with capacitive discharge, suggesting that the DC feed at the exchange was at fault. Using a digital display would have just produced a rapidly-changing numerical display.

I remember reading that the BBC did install digital clocks in their studios, but had to quickly reinstate the analogue ones as users found it much more difficult to rapidly work out how much more time was remaining from the numeric displays. With an analogue clock, you could just glance at the clock face and gauge how time was left by the angle of the hands rather than having to do mental arithmetic, and they did not require 4- or 6-figure digital accuracy.
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Old 25th Mar 2017, 8:13 pm   #17
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Default Re: The swing of a needle vs accuracy and direct readout

Quote:
I remember reading that the BBC did install digital clocks in their studios, but had to quickly reinstate the analogue ones as users found it much more difficult to rapidly work out how much more time was remaining from the numeric displays. With an analogue clock, you could just glance at the clock face and gauge how time was left by the angle of the hands rather than having to do mental arithmetic, and they did not require 4- or 6-figure digital accuracy.
Definitely, I concur with that. It's the same with a lot of touch control volume control stuff these days. The music you're listening to isn't the same constant volume every second, so for the few seconds that you're touching the control you don't really have much feedback as to how much effect your 'touching' has been. On the other hand, if you want to say lower the volume of a radio or a hifi amp with normal rotary volume control, then if it is say at '7', you're going to turn it down to, I dunno, 4 or 5, and not only does that 'have a meaning' in your neural network, you'll actually hear an instant dip in the volume; not so with touch control, it's more gradual, and if there's a gap or a lull in the music it's even worse. When those electronics and radio pioneers designed those radios and hifis all those years ago, they knew that a rotary analogue control would work better than a digital touch control one, and they made the right choice.
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Old 25th Mar 2017, 9:23 pm   #18
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Default Re: The swing of a needle vs accuracy and direct readout

I have a Metrix DMM I bought in the early '90's I think. Very good unit, never any trouble. It will flatten its battery if left on for weeks, but I think it has only had about 4 batts so far. It got left on for a week about one month ago.
I also have a Tandy, sold to me cheaply by a guy who got it in a Tandy sale about 25 years ago. I don't use it much, but it works perfectly. It is manual or auto ranging, and has a socket for the built in transistor tester, with a DECENT plug with three small clips for any none-fitting transistor testing.
I bought a tidy Philips meter, with the red LED readout scale. It took 4 (I think) C cells, but would flatten them overnight if left on, so it had to go. I later saw the equivalent Philips with similar sized (big) LCD display. Probably better, but the LED one was so easy to read.
I have other DVMs, but my analogues are mostly GEC Selectest.
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Old 25th Mar 2017, 9:56 pm   #19
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Default Re: The swing of a needle vs accuracy and direct readout

Hi,
There are some other Analog and Digital Display_dualmetering_ equipments to buy, and I wished to write over an Philips Type too, but Les was earlier on...
Karl
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Old 26th Mar 2017, 7:35 am   #20
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Default Re: The swing of a needle vs accuracy and direct readout

For sure, the dual analogue/digital meters seem to work best when the analogue part is a proper, old style 'meter' and not a crude digital attempt at one.
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