Hi & Thanks for the valuable feedback. I agree with all your comments about my eBay listed AC & Resistance calibrator modules.
I don't make excuses when constructively criticized but I do like to clarify as to the limitations that you have accurately pointed out.
"With regard to this recent post of two eBay "references", I unfortunately have many concerns with them:
- general issue with having to buy many references as mentioned above
- these specific references are not really precise enough to be considered appropriate for calibration purposes
- stability is not mentioned
- multiple problems with the general construction of the references, such as no enclosures or board stand-offs, awkward connection points and use of universal proto-boards rather than a manufactured PCB
- apparently the maker only has a calibrated Fluke 87V which is not really good enough for providing calibration data
- future calibration services are not mentioned"
As I said in my initial post, my eBay devices are designed for the under-$100 DMM owner who wants to verify the readings of his/her Chinese cheapie DMM. Such DMM's are usually manufactured to be self-calibrating and non-adjustable so, verification is the only owner option for this ubiquitous category of cheap DMM's.
All of my eBay listings are intentionally vague on specifications so that I don't mislead buyers into thinking that they're going to receive a laboratory-quality or NIST-traceable device. These are really just hobbyist-grade but very useful and VERY accurate.
Here's an example using the AC Sine Wave module: After 15-minute warmup, in a 78 degree, non-drafty environment, attached to the matched Power Supply module, the AC Sine Wave output will stabilize at 6.000VACrms, +/-2mV and hold that voltage for several hours. I think that's pretty good for a $39 Sine Wave generator with a 6Vrms, low-impedance output, huh?
And, it certainly will indicate whether your cheapie DMM is working properly at low AC ranges where most such DMM's self-calibrate. My instructions clearly state that a "good reading" on a 0-6VAC range doesn't necessarily equate to a valid reading at hgher and dangerous AC ranges. But, the AC Calibrator does provide a useful, stable, non-fluctuating Sine Wave that is so necessary to be able to reasonably accurately READ a DMM's AC display, right?
To keep selling costs at a minimum, I offer these modules simply as modules to the DIY'er who are familiar with what they can do with modules and not as finished products which sophisticated calibration freaks like myself would be attracted to!
Therefore, I sell hand-wired perf boards, no standoffs and clunky header pin connection points. For the module DIY'er, these are not deal-breakers.
And, yes, I love and use my calibrated 87V's. They certainly speed up breadboarding custom designs and module revisions. My $1,000 calibrated Keithley 2110 5.5 Digit Multimeter with Dual Display just keeps watch over my Fluke Fleet. ( like that: Fluke-Fleet!
) I do use the K to calibrate all my amateurish products before they're listed, though.
Finally, there is no mention of re-cal of any of my modules because of their intended use. But, if anyone who buys one wants to re-cal, I would do it for free as long as they pay shipping back & forth. Same for repairs unless they let the magic smoke out of the entire module.
So, none of my products are of lab-quality nor, in the class of a DMMCheck or other high-precision test or reference equipment. That market is well-served and too pricey for old, fixed-income geezers like me.
Again, Thank you for your valuable feedback. You have given me the opportunity to clarify and I appreciate that.