True RMS vs averaging DMM

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sodderboy said:
I checked it, and although the 8060A can calculate dB DC, I cannot think why I would need it.
On the DC scale I am testing blood pressure (+/-V) and nervous system (various) voltages to numerical values not converted to dB. I'll re-read the 8050A post.
"The plus rail is down 3 dB" said me never.
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I use DC as a stimulus to check an attenuator (often stepped) rather than tone then use the 8050's DC dB and relative modes to read attenuation directly in dB.
This method seems to offer better measurement resolution and noise immunity.
The 8050A and 8060 both inject quite a bit of noise into the test leads.
My "0 dB" reference is often +10.000 VDC.
 
abbey road d enfer said:
The product I would like to buy apparently does not exist.
An auto-ranging DVM that displays simultaneously the DC content (average DC), the AC rms value and the peak-to-peak AC value. No need for AC average then.
The missing link netween DVM and 'scope.
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Your post reminds me of this multi-mode analog meter:

https://proaudiodesignforum.com/forum/php/viewtopic.php?f=12&t=688
Some of the B+K Precision bench meters have dual mode displays and start around $500 US.

https://www.bkprecision.com/products/multimeters#bench
To answer another post the 8050 has a "Zebra strip" transition from the display board to the LCD.
IIRC the LCD is snapped into a plastic box and the Zebra strip connects at right angles the LCD to the PC board.
I've never had a problem with the flex main board-to-display board ribbon cable but its a good idea to clean the board where it mates to the ribbon.
 
sodderboy said:
It's deeper than the ribbons. If it's like the '60A the LCD is connected to the PCB with a conductive rubber spacer that needs to have it's contacts cleaned. Have not had to do that often, but it works.
Mike
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I remember taking apart the LCDs and cleaning them in the case it might have been a conductivity issue, no dice..
 
57sputnik said:
Your post reminds me of this multi-mode analog meter:

https://proaudiodesignforum.com/forum/php/viewtopic.php?f=12&t=688
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Actually I was considering building the meter I described. I came to a somewhat similar arrangement except that I want the triple display (I'm not interested in Average).
This made me think: "do I need to measure positive and negative peak?" I think I just need peak-to-peak...

I could as well 3 DMM's, one in DC mode, the other in AC mode and the third with the addition of a peak rectifier, but it would take too much space on my bench.
 
The 8050A has a version with a battery charge light and one without. I think that means one has a battery and one doesn’t? For common to be floating do you need the battery version?
 
Gold said:
The 8050A has a version with a battery charge light and one without. I think that means one has a battery and one doesn’t? For common to be floating do you need the battery version?
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The charge light is the visible difference between the 8050A and the 8050A-01 (battery-powered).

Both the battery-powered version and the line-powered version have the "-" probe lead "isolated" from AC ground by a 47MΩ resistor. Not completely floating but close.
 
I always used apples to explain dB, and have never needed them when dealing with VDC.
PS: when in deep over a L-R monitor imbalance, mic lines issue, difference between console channels, etc. I have called dB "dooshe bags".
I confess, and I apologize. . .
Mike
 
My Uni-T 171b can give both AC and DC measurements simultaneously via the dual display ,also min/max and average reading , its a function I havent used much to be honest , the basic accuracy next to the other fluke meters isnt all that great . I probably should look at trying to better calibrate the Uni-T with the known good 187 as a reference .

Just to go back and answer Abbeys question about the original source voltage on my test , it was from a Martindale 440v proving unit , no guarantee it puts out a sinusoidal waveform , so maybe thats where the error crept in.
 
Looks like Ive got another Fluke meter on the way , model 177 true rms ,
Some small signs of wear on the face plate ,but in good working order ,
no test leads , 60 euros , too good to miss . I see ex British army Fluke model 25 meters going reasonably too , I'd emailed a seller to check if he had any he was willing to sell for parts or repair but heard nothing back .
They come in a hardshell case and are extremely rugged , probably make a good tough meter for the tool box .
 
Re Fluke Handheld meters--most have very limited AC accuracy even if they claim to be TRMS. The 177 is rated 1% +3 digits 45-500Hz. My Agilent U1253B 4.5 digit is a bit better at 1.5% 20Hz-15kHz, or 3.5% to 100 kHz + 120 digits. Bench DMMs (Keysight, Agilent, Keithley, etc.) are much better & more expensive.
 
I have the 187 if I need better accuracy from a multimeter but Im not allowing the metrology bug twist up my melon ,I dont need 8 digits accuracy so I end up fixated with stuff going on at a molecular level that I can do nothing about , A soundcard and REW beats the ass off most handheld meters for audio measurements and if you get the right interface its up there with the best audio test kit for a small fraction of the price . Im very glad now I didnt bother with a digital standalone scope , I have the visual splendor of the analog TEK and the number crunching power of the PC spitting out numbers slightly behind real time . What I want now is a cathode follower probe to test mic capsules and other audio sources with minimum loading effect.

I'll try my B&K cathode follower preamp/2801psu's , The cathode follower should have no difficulties driving the scope ,the multimeter and a hi-z instrument input , the 2801 also has the option of a transformer balanced audio output built in . The capsule bias voltage is variable via preset pot inside the unit , normally its trimmed to 200v for B&K capsules ,but no reason that cant be changed to a more suitable range for the usual LDC or SDC's .
 
moamps said:
Here is a Quora type question intended especially for those members who think that DIYers do not need oscilloscopes, but that a DMM is sufficient.
The linear power supply consists of a transformer, a full-bridge rectifier, a capacitor and a 7812 regulator. The regulator needs a minimum ratio of Vin-Vout=3V to work properly.
Average DMM in DC position measures 17V at the reg input. What is the maximum voltage that can be measured in the AC position at the reg input for the regulator to work correctly?

View attachment 96514
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So first guess is 2Vac, but since that's avg. and peak must be accounted for, it would be the top, second formula, restated to solve for A. So A= 2Vac * (2/pi) = 1.27Vac. I'd say 1.25Vac to be safe.
 
RogerAF said:
So first guess is 2Vac, but since that's avg. and peak must be accounted for, it would be the top, second formula, restated to solve for A. So A= 2Vac * (2/pi) = 1.27Vac. I'd say 1.25Vac to be safe.
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Pi is not relevant here.
The limit is an instantaneous value of 15V, which is 2V below the average value. Let's take this peak value of 2V. The waveform of ripple is constituted of a broken segment of sinewave and a segment of exponential. In a decent system, the two segments can be assimilated to straight lines, so we can use a triangle waveform for the actual ripple waveform.
The average value of a triangle wave is half its peak value, so the averaging meter should indicate less than 1V for correct operation. A true-rms meter should register about 1.15V.

P.S: I'm not the teacher here. :D
 

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