Analog multimeter jacks - Page 1
Forum section: electronics / testgear

author: FenderBender
author_rank: Super Contributor
timestamp: December 10, 2012, 03:28:34 am
content: Hello,For my birthday, one of my relatives got me an analog multimeter kit. I've always wanted a AVO and it looks like the one I'm going to build up is a pretty good one.Now, I've used an analog meter but none of them have had this. I've searched through the manual but I'm still confused!1.) What is this "Output" jack used for? From what I read, if you have an AC signal with a DC offset or something? How would you hook it up?2.) It looks like you can measure up to 250mA using the "P" and "N" jack. If I wanted to measure up to 10A (which I wouldn't dare! Unfused!), I would have to use the "10+" jack and...."N"? or is it "P"?3.) What is DCV NULL?Thanks so much in advance!

author: grenert
author_rank: Frequent Contributor
timestamp: December 10, 2012, 04:15:01 am
content: Quote from: FenderBender on December 10, 2012, 03:28:34 amA null meter allows you to balance voltages between the + and - terminals (the two voltage sources have their grounds tied together). The null setting places the needle at the center of the scale, which then becomes zero. There is a special blue scale on the dial which shows you the scale for the null function which has a zero in the middle. See the little centered needle in the picture next to the ohms zero knob? You would use that to adjust the needle to the middle to prepare for a null measurement.Have fun building your meter!

author: FenderBender
author_rank: Super Contributor
timestamp: December 10, 2012, 04:40:22 am
content: Thanks for that! I'm sure this is probably all obvious to many of you. Unfortunately, I kind of missed the whole analog meter era.

author: Bored@Work
author_rank: Super Contributor
timestamp: December 10, 2012, 06:26:15 am
content: www.elenco.com/admin_data/pdffiles/m1250.pdf

author: FenderBender
author_rank: Super Contributor
timestamp: December 11, 2012, 01:16:46 am
content: Quote from: Bored@Work on December 10, 2012, 06:26:15 amI did read that. Just wondering if someone could elaborate on that whole "Output" thing.But thank you!

author: c4757p
author_rank: Super Contributor
timestamp: December 11, 2012, 01:33:46 am
content: Looking at the schematic, the "output" jack seems to be AC coupled to the input. Not sure why that would ever be useful, and seems a bit of a safety issue to me. Probing AC, the full voltage will be on that jack with nothing plugged into it, just waiting for something to fall in, at an impedance of about 56K for 60Hz mains, giving a couple of milliamps. Personally I would probably leave out C1 to disable the jack.

author: Harvs
author_rank: Super Contributor
timestamp: December 11, 2012, 01:35:39 am
content: Attached is a cropped screen grab of the schematic diagram in that manual. The "Output" terminal is nothing more than the pos terminal with a coupling capacitor.Hence in the manual it talks about measuring a AC component with a DC offset. So using the "Output" terminal instead of the pos you'll block any DC component, same as AC coupling on a oscilloscope.God knows why they called it "output". From the logic in my brain it's got nothing to do with outputting anything. They could have simply called it AC coupled.

author: robrenz
author_rank: Super Contributor
timestamp: December 11, 2012, 01:35:54 am
content: From the manual you readOutput Jack Test (allows measurement of AC voltage when superimposed on a DC voltage.)1. Plug the red lead into the OUTPUT socket and the black lead into _COM.2. Set the range switch to the appropriate ACV position. Touch the test leads to the power source and observethe reading. Then, multiply by the appropriate scale factor.Translation: Capacitor coupling of signal to eliminate DC component and read only AC component.

author: FenderBender
author_rank: Super Contributor
timestamp: December 11, 2012, 01:38:36 am
content: Hmm well I'll be darned....Don't get why it's called "Output"?But yeah that's precisely what I thought from reading it, but I didn't think there would be a dedicated jack for it?

author: Tube_Dude
author_rank: Regular Contributor
timestamp: December 11, 2012, 01:40:27 am
content: Quote from: FenderBender on December 11, 2012, 01:16:46 amIt's all in the pdf..."Output Jack Test (allows measurement of AC voltage when superimposed on a DC voltage.)1. Plug the red lead into the OUTPUT socket and the black lead into _COM.2. Set the range switch to the appropriate ACV position. Touch the test leads to the power source and observethe reading."Edit- Robrenz was faster...

author: FenderBender
author_rank: Super Contributor
timestamp: December 11, 2012, 01:54:36 am
content: Yeah thanks I got it. I was convinced it meant some sort of external output, like to a scope or something?!?! I don't even know.I'll just shut up now.Thanks guys.

author: Tube_Dude
author_rank: Regular Contributor
timestamp: December 11, 2012, 02:04:41 am
content: Good examples of measurement of AC voltage when superimposed on a DC voltage, is to measure the AC ripple in the main filter capacitors of a DC power supply, amp, DC power rails,....

author: FenderBender
author_rank: Super Contributor
timestamp: December 11, 2012, 02:08:23 am
content: Quote from: Tube_Dude on December 11, 2012, 02:04:41 amScope works too, but it's a simple neat tool I'd say.

author: Tube_Dude
author_rank: Regular Contributor
timestamp: December 11, 2012, 02:12:44 am
content: Quote from: FenderBender on December 11, 2012, 02:08:23 amSurely scope too, but when you don't have a scope around, or in field conditions...

author: T4P
author_rank: Super Contributor
timestamp: December 11, 2012, 04:21:46 am
content: In the past i had a Sanwa (which they cloned, but it didn't have transistor sockets which they never had) and the 'OUTPUT' jack for connecting to the bases of transistors

author: FenderBender
author_rank: Super Contributor
timestamp: December 11, 2012, 06:10:18 am
content: Yeah this one seems like a pretty good kit. Quality of the plastic, components and everything is top notch. I'll get some pictures up when I assemble it. Working on fixing up my soldering setup first so I can produce some good results on this.

author: mzacharias
author_rank: Frequent Contributor
timestamp: December 11, 2012, 11:09:18 am
content: Quote from: FenderBender on December 11, 2012, 01:16:46 amFor use at the plate of a tube amp or maybe inside the coupling cap of a single-ended transistor amp. Virtually useless these days. We just use the AC coupled setting on a 'scope for this.Back then 'scopes were too expensive for most people (good ones anyway).

author: FenderBender
author_rank: Super Contributor
timestamp: December 13, 2012, 02:13:34 am
content: Righto! Thanks.