Randall 6/25/2018 7:23 PM
meter calibration
How often do you guys have your meter calibrated? Where do you send it, and how much does it cost? I have a Fluke 77 IV that is about 6 years old and has never been calibrated. How necessary is it, or is it close enough for what we do?
 
Chuck H 6/25/2018 7:46 PM
How much would it really affect the repair or building of guitar amps if a meter was off by five percent? And if it was off by that amount you would probably know because everything would seem a little off. I have never had a meter calibrated.
 
The Dude 6/25/2018 7:46 PM
Here's what Fluke says:

https://us.flukecal.com/blog/how-oft...-you-calibrate
 
nosaj 6/25/2018 7:56 PM
Quote Originally Posted by Randall View Post
How often do you guys have your meter calibrated? Where do you send it, and how much does it cost? I have a Fluke 77 IV that is about 6 years old and has never been calibrated. How necessary is it, or is it close enough for what we do?
For the ohms you could see how far it's off with a 1% resistor.

Most of the older tube circuits use +-20% so whatever makes you feel more confident in your tools. A questionable tool will always have you wondering if its you or the tool.

nosaj
 
g1 6/25/2018 9:28 PM
There is one trimmer in my old 77 for cal., not sure about the IV.
Agree with nosaj suggestion about a 1% resistor. I did mine by plugging the probes in to the wall outlet and twiddling the trimmer till it was in agreement with my other meters, but Elmer the Safety Elephant was "not too keen on that" as they say.
 
Enzo 6/25/2018 9:34 PM
Labs need calibration. FLuke makes all kinds of stuff. The basic stuff like the 77, and the high-falutin fancy lab stuff with 18 digit readouts and four-wire inputs. That calibration guide was aimed more at the lab crowd.

I have never calibrated my meter. Close enough is close enough. If in doubt, take a few meters and measure something. A resistor, a 9v battery, the AC voltage from the wall, whatever. How close to the readings compare? Nosaj' suggestion of a 1% resistor is good too. Hell, next time you ordr parts, throw a few 0.1% resistors on there, they are cheap enough.

Somewhere I have a few resistors that are some sort of standard. They are some kind of film resistor - you can see the spiral gap running around the inner element. The element is within an evacuated glass tube. And the writing on it claims 1.0000001 meg ohms.
 
The Dude 6/25/2018 9:49 PM
Quote Originally Posted by Enzo View Post
......That calibration guide was aimed more at the lab crowd......
Agreed. The main reason I posted the link was for the last part.

Never. If your work requires just gross voltage checks (“Yep, that’s 480 V”), calibration seems like overkill. But what if your instrument is exposed to an event? Calibration allows you to use the instrument with confidence.

And, if your meter is "exposed to an event", it's likely going to need repair anyway. Calibration would be part of the repair.
 
g1 6/25/2018 9:51 PM
Well, the IV does not seem to be the simple setup as the old version I have.

https://www.manualslib.com/manual/73...7.html?page=14 (series IV)

https://www.youtube.com/watch?v=9ptPe_AeZiQ (series I)
 
Randall 6/25/2018 10:33 PM
Decades ago i worked in television at a local NBC affiliate in the engineering dept. I maintained various microwave equipment, and part of the job was doing monthly FCC frequency measurement logs with an expensive HP spectrum analyzer. Every so often I had to travel to Bath Iron Works shipyard in Maine to get it calibrated by a military certified station. It was done by some old guy who worked in a screened in cage inside the facility. Signed off, stickered, traceable, certified. That was serious calibration for high end equipment required by the government. So that I get about calibrating the serious stuff.

So as for my little meter, I suspected it isn't a big deal, but was curious how others approached it. I get 0.1 ohms when shorting the leads, and voltage is always pretty relative, so I guess I will not worry about it and sleep well tonight.
 
Enzo 6/25/2018 10:45 PM
Shorting the leads pretty much tells you about the leads rather than the meter. But for any low ohms measurement that should be the first step.
 
Chuck H 6/25/2018 10:46 PM
What I honestly wonder about sometimes is whether the null measurement is at all relative to the factory probes or some other industry standard.?. That is, why aren't these things calibrated to a null of ZERO with the leads they're shipped with?!? But for finer measurements I take a null reading and subtract it. I can't imagine the actual range measurement is ever significantly different than the meters specified accuracy.

So why aren't the meters calibrated to zero with factory probes OR have a null button on the panel?
 
Enzo 6/25/2018 11:01 PM
In the days of VTVMs, there was always a zero set knob on the resistance scale. You short the leads and turn the knob to set the dial to zero. Then your took your readings. To do that on a modern DMM would require a panel control. Hardly worth it. I suppose you could make some existing button dual pirpose for this function. MOST readings are not of an ohm or less. The probe resistance is not at all an issue measuring 220k or 1.5k or most anything else in a guitar amp.

You could engineer the thing to include specific probe resistance, but then when you replace probes? Who can guarantee making probes that all have exactly the same resistance. Resistance includes the contact surface of the probe tips too. They get dirty or oxidized...

I think anyone who lives in a world that makes then take fractional ohm readings all day long would have a meter specifically set up for that task, like a four-wire.
 
J M Fahey 6/26/2018 12:01 AM
Going to sleep now but tomorrow IŽll post my low ohm meter thingie:
* 2 ohm full scale
* resolution 0.01 ohm
* reads zero if you short probes
* no calibration really needed , you can fine tune it if you wish
* use your multimeter as display.
* grand total of 3 parts , plus hardware (banana plugs or crocodile clips, battery holder, n.o. switch, some kind of case).
* estimated cost around $5

EDIT: almost forgot :to protect some weakling multimeter, you might splurge and add 1 (one) extra part and spend extra 5 or 10 cents .... sorry if this ruins your Retirement plans .
 
Leo_Gnardo 6/26/2018 5:27 AM
Quote Originally Posted by J M Fahey View Post
Going to sleep now but tomorrow IŽll post my low ohm meter thingie: - - - - estimated cost around $5
KOOL! Imma lookin' forward to this.

- - - - - - - - -

DC calibration: at one time way long ago, the field test for DC was to measure across a brand new carbon zinc D battery. I'm certain a C or AA would suffice. We expect to see 1.56V.

Dynaco used to use some odd value resistor - was it 11.3 ohms? - in the cathode circuit of MkIII and Stereo 70 amps. The idea was, for testing bias current the amp would develop 1.56V across the resistor, and you could check the accuracy of your meter beforehand by testing on a carbon zinc battery. There weren't any fancy-dan alkaline nor other small batteries back then.
 
nevetslab 7/11/2018 12:09 AM
While I do have some calibration instruments in my inventory, it's been a good long time since I've made use of them. Relative calibration and agreement between instruments is what I rely upon. I've been using Fluke 8060A 4.5 digit DMM's for years, and they still read very accurately when connected to my ESI Dekabox 6-dial 1 ohm to 1.100000M. For daily bench work, I never give it a second thought, having relied on quality lab gear that agrees with each other. If I find one of my instruments reading off, such as my Philips PM2535 System Multimeter in AC Volts mode, I make note of it, but, it also has a Relative Mode, so I can still get around the issue. In general, I'm pretty sure my daily dirt instruments are in the 2% accuracy range with each other. I can't afford yearly calibration fees, and never have paid them. Relative calibration is good enough!!
 
Helmholtz 7/11/2018 6:53 AM
It makes sense to check and clean (Deoxit) fuse holder contacts of meter fuses after some years. The problem may not be noticeable in V mode but give wrong current and Ohms readings.
 
Chuck H 7/11/2018 6:58 AM
Quote Originally Posted by Helmholtz View Post
It makes sense to check and clean (Deoxit) fuse holder contacts of meter fuses after some years. The problem may not be noticeable in V mode but give wrong current and Ohms readings.
Great note. Something a guy like me doesn't even consider since I'm only at my bench a few times a year anymore. And all that sitting around can only make the oxide problem worse too. Here's another
 
drewl 7/11/2018 7:45 AM
I used to work in a Metrology lab, repairing and calibrating all kinds of test equipment.


Stuff in the lab at work is calibrated, so every once in a while I'll check my own equipment against that.

For troubleshooting or repairing amps meters don't have to be too accurate.
 
loudthud 7/11/2018 10:04 PM
I have a Fluke 85. It has a REL button. Short the probes on Ohms and hit the REL button and it zero's out the probe resistance.

Whenever I go to a Pawn shop, I checkout the display case where they keep the meters. Sometimes you can find a bargain. One time I found a 2 Amp Variac for $15 because they didn't know what it was. Back when I ran a business, an extra meter or two came in handy. Never found a Fluke meter that had any significant calibration problem other than a blown fuse or worn out probe lead.