Products > Test Equipment
Reference PCB for Calibrating DMM's
Gyro:
No. Precision wirewound resistors are going to be using specific alloys (Manganin, Constantan etc) and minimal stress windings. The only real purpose of one of those bog standard wirewounds is to dissipate heat, so no real care in construction.
Yes, wirewound resistors can still drift. Changes in composition (you specifically don't want to dissipate heat in a precision resistor), Winding stresses (if the wire gets too tight on the former it will stretch and get thinner!) etc. NOTHING stays constant forever, but with close attention to construction in precision parts, you can minimise it. The mouser resistors aren't precision in the 'laboratory resistance standard' sense, they are just 'good'. The Tayda are neither in this context.
Cement resistors transition from wirewound to film at some arbitrary value, depending on size (the wire gets too thin and hard to wind at some (price)) point.
JenniferG:
--- Quote from: Gyro on November 24, 2022, 05:38:36 pm ---No. Precision wirewound resistors are going to be using specific alloys (Manganin, Constantan etc) and minimal stress windings. The only real purpose of one of those bog standard wirewounds is to dissipate heat, so no real care in construction.
Yes, wirewound resistors can still drift. Changes in composition (you specifically don't want to dissipate heat in a precision resistor), Winding stresses (if the wire gets too tight on the former it will stretch and get thinner!) etc. NOTHING stays constant forever, but with close attention to construction in precision parts, you can minimise it. The mouser resistors aren't precision in the 'laboratory resistance standard' sense, they are just 'good'. The Tayda are neither in this context.
Cement resistors transition from wirewound to film at some arbitrary value, depending on size (the wire gets too thin and hard to wind at some (price)) point.
--- End quote ---
Thanks, constantly learning in this hobby; having fun :) I think what I am going to do is take some Royal Ohm 1 cent metal film resistors (1%) , say like 3 of them, to my local electronics store and see if they'd kindly measure them for me on a calibrated scope :) Then perhaps go there every year with the same resistors to see how they drift and to update the values if changed. I need some local electronics buddies -- I'll have to look into that.. can share resources and ideas to save money, etc. :)_ I wonder if I should bring my probemaster leads if that makes a difference.. I imagine using the same leads on both unit and the calibrated unit would help?
ci11:
Getting components one at a time may still leave you wondering if other measurements and values are within spec, and perhaps more importantly, whether the specific ones you received from the likes of Mouser are actually on the mark. Calibrations are expensive at labs because the calibrators they use are very expensive, and for good reason. One alternative for hobbyists is be the DMMCheck plus and there are others. Many DMM users like the DMMCheck as a quick and easy way to know if their meter is good to go or needs work. It's not inexpensive but it is worth mentioning Just Google "DMMCheck Plus".
bdunham7:
--- Quote from: JenniferG on November 24, 2022, 11:34:16 am ---If I bought this, I am wondering if I could take it to my local electronics store and have them (or pay them) to record the results for voltage and resistances onto the pcb. Or perhaps someone here sells those boards with values they recorded from a very good calibrated meter?
I just need a reference to see which of my meters is off.. the 8251A or the UT61E. I want to see how close both are to actual values. I also need a reference in case I need to calibrate a meter.
--- End quote ---
I've yet to see an electronics store that has a calibrated meter on hand. Actually, it is getting hard to find a retail electronics store of any kind these days.
The real enemy of your plan is tempco. The temperature coefficient of typical parts causes their values to move around and this will probably be the main source of error in this sort of endeavor. I doubt the $13 reference will be excellent in this regard. The typical good-quality entry-level calibration checker is the DMM Check, which goes for $100 or so.
These are all OK for checking your DMM, but would not be suitable for actually correcting the calibration. That requires a much more comprehensive set of precise stimulus voltages. In the case of the GDM-8251, at least with mine, I found that the entire tolerance specification (and maybe a bit more) was taken up by the in-range (+/- 5C) tempco of the unit. IOW, it wasn't really stable enough to benefit from calibration. I'm not saying you should chuck it in the trash, but just keep your expectations reasonable!
I'd say that if you don't want to spend the money on a DMM Check right now, get the $13 unit and have someone check it for you. Are your two meters not in agreement on things that you measure? If so, how much are they off?
coromonadalix:
--- Quote from: JenniferG on November 24, 2022, 05:45:26 pm ---
--- Quote from: Gyro on November 24, 2022, 05:38:36 pm ---No. Precision wirewound resistors are going to be using specific alloys (Manganin, Constantan etc) and minimal stress windings. The only real purpose of one of those bog standard wirewounds is to dissipate heat, so no real care in construction.
Yes, wirewound resistors can still drift. Changes in composition (you specifically don't want to dissipate heat in a precision resistor), Winding stresses (if the wire gets too tight on the former it will stretch and get thinner!) etc. NOTHING stays constant forever, but with close attention to construction in precision parts, you can minimise it. The mouser resistors aren't precision in the 'laboratory resistance standard' sense, they are just 'good'. The Tayda are neither in this context.
Cement resistors transition from wirewound to film at some arbitrary value, depending on size (the wire gets too thin and hard to wind at some (price)) point.
--- End quote ---
Thanks, constantly learning in this hobby; having fun :) I think what I am going to do is take some Royal Ohm 1 cent metal film resistors (1%) , say like 3 of them, to my local electronics store and see if they'd kindly measure them for me on a calibrated scope :) Then perhaps go there every year with the same resistors to see how they drift and to update the values if changed. I need some local electronics buddies -- I'll have to look into that.. can share resources and ideas to save money, etc. :)_ I wonder if I should bring my probemaster leads if that makes a difference.. I imagine using the same leads on both unit and the calibrated unit would help?
--- End quote ---
excuses me 1% resistor as a reference is pure #$##^ you need at least 0.0xx percent precision resistors i have 0,0014% ones from an old calibrator, even theses will be affected by temperatures and or humidity
precision stuff like, meters have warm up times, precision references too, precision resistors etc ... you are venturing in a different world when you talk about precision references
an 6.5 digit meter cost me 160$ CAD, i had 3x oldies hp 34401A meters, and now i've switched to more modern stuff, it cost a little bit more ...
i have 300,000 count Gossen Metrawatt meters, same price here 160$ cad for each ...
I mean like others you need some references points before thinking doing some precisions stuff, grab an 5.5 digits or more meter and make it calibrated and keep it clean and stabilized in temperature and humidity
That's why people love old meters like the 34401a, when working perfectly they have "aged" very well and got pretty stable over the years, one i had was almost 25 years and was pretty close to "calibrations standards" even calibrated 10 years after the last calibration sticker
You could buy a precision reference divider network like the ones we find in meters, they can go up to 20-25$, they will be way better than the 1% precision idea
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