Digital Multimeters.

[lord loh.]

Several Digital Multimeters have specifications like 3 3/4 digit multimeter.
**broken link removed** Multimeters

What does 3/4 and 4/5 mean ?

What is the use of a multimeter with a bargraph? What does the bar graph display?
https://mecoinst.com/catalog/details.asp?product_id=24

Added Later:http://metravi.com/901_II.html
Caims the multimeter to have "This is a 3-3/4 Digits 3999 Counts Autoranging Digital Multimeter"
What does the 3999 Counts mean ?

Thanks in advance.

 

[upand_at_them]

Although they don't explain it, the product descriptions give you enough information to figure out what 3-1/2 digits and 3-3/4 digits mean.

3-1/2 digits, 1999 count:
1999 is the maximum number it can display. Three nines are three full digits and since the first digit can only display a one it is called a 1/2 digit.

3-3/4 digits, 3999 count:
You get the idea.

As for the bargraph...I've never used or needed one. Seems like it's trying to be like a analog meter, which isn't a bad thing.

Mike

 

[lord loh.]

3-1/2 digits, 1999 count:
1999 is the maximum number it can display. Three nines are three full digits and since the first digit can only display a one it is called a 1/2 digit.

3-3/4 digits, 3999 count:
You get the idea.

Thanks for the explaination...

If I go along the second explaination, why shouldn't the firstone be called 3-1/4 Three full digits and one that can display only 1 2 or 3....

None of my instrumentation text books speak anything about this....

Thank you.

 

[fsahmed]

If u have used a meter with bar graph, u will notice that it gives u the value much faster than the digital display. This is its sole function, digital conversion takes time since it requires processing. Hence digital meters r slower than analog ones because the needle moves faster than the conversion. The bar graph is incorporated into digital meters for speed, it comes useful when u r troubleshooting, gives a general, relative idea of a value very fast, u dont have to wait for the actual figure to appear on the display.

 

[lord loh.]

Thanks fsahmed, I did use a bar graph meter once but only once and did not get much of an opportunity to observe it. I thought it showed the point that the measurement is occurring in the particular range.

My question about the 3-1/2 digit and 3-1/4 digit still remains.

And has anyone used TRMS? Can anyone give me a place where one could not do without TRMS?

If my understanding is correct, True RMS is the measure of an AC riding on a DC...

 

[Nigel Goodwin]

Thanks fsahmed, I did use a bar graph meter once but only once and did not get much of an opportunity to observe it. I thought it showed the point that the measurement is occurring in the particular range.

The bar graph facility is for doing adjustments, often you need to adjust a circuit for a peak or a dip - a digital display is next to useless for this, but an analogue display makes it simple, so the bar graph simulates a simple analogue meter.

My question about the 3-1/2 digit and 3-1/4 digit still remains.

Same as before really?, a full four digit meter would read to 9999 (and would probably waste range?), but most digital meters only read to 1999 - so they called this 3-1/2 digits. Later on some meters started going to 3999 instead, so they called this 3-3/4, it's just a name, it doesn't really matter!.

From my point of view, 3-3/4 is ideal, the 399.9V range covers almost everything I ever need, without range changing :lol:

And has anyone used TRMS? Can anyone give me a place where one could not do without TRMS?

Measuring ANY non-sinusoidal AC waveform.

If my understanding is correct, True RMS is the measure of an AC riding on a DC...

NO! - it's measuring an AC waveform of ANY shape, a conventional meter ONLY reads the value of a sinewave, it actually reads 'average', and it's calibrated for that average to be the same as a sinewave. If you try and read any other wave (for example a square wave) it will give completely the wrong reading.

 

[Dean Huster]

I think that few people really NEED true RMS capability for most run-of-the-mill measurements. We're usually working with sine waves, so the average-measure, rms-display meter works for 99% of the stuff you need. You know, we've gotten along pretty well in the years prior to the commonly-available true-rms meters, haven't we?

Whenever you have complex waveforms to measure, you're usually using an oscilloscope and looking for a lot of different characteristics that you can't see on a DMM, such as risetime, fall time, glitches, sag, pulse width, period, etc., especially on an incredibly-complex waveform such as a composite television signal.

I don't much like the bargraph on a DMM simply because it has stepped resolution. Each bar turns on only after you're reached the next step in the bargraphs range and that step may be a lot larger than you can tolerate if making fine peak or nulling measurements. A good example would be that of using a DMM with a good ACV frequency response to null out a homemade THD analyzer. You'd never see the best null with the DMM and that could affect the final measurement tremendously. If you need an analog meter's capability, use an analog meter!

Dean