'Affordable' Reference Standards to Have On-Hand in a Electronics Lab

[alm]

What do you guys think about the Time Electronics 1017 DC V/I/R Multifunction Calibrator?
https://www.timeelectronics.com/portable-voltage-current-instruments/1017-voltage-current-resistance-calibrator/


I know that this is not a "standard" but a "calibrator" (whats the difference anyway? A standard also needs calibration, does it?)
But looking at the specs it seems to me that this could be a "cheap" standard-option?

It depends on what you need in terms of accuracy and values. Keep in mind that the instrument has only a single resistance and current range, so if you are near the bottom of the range accuracy and resolution won't be so great. For example resistance accuracy is 0.05% of full scale, so setting it to 10 Ohm would have an uncertainty of 5 Ohms. Stability and resolution will be better than this. So if had another meter, you could adjust it so it read 5 Ohm +/- 0.01 Ohm on that meter.

I'd say a standard in general has a single or a few values, like the AD584 voltage standards that can output 2.5/5/7.5/10V or the DMMCheckPlus. And is focused on stability rather than flexibility. While a calibrator while usually be able to produce a larger range of values, like this example which can range DC voltages, currents and resistances through quite a range. In a cal lab, you would have calibrators doing the daily calibration of all the devices that come in, and use the standards once in a while to verify and/or adjust the calibrators.

Both need calibration and you could use a standard for calibration (if it happens to have the value you need), and you could use a calibrator as standard. It's just that calibrators are often larger and heavier so less practical to ship around than a small voltage or resistance standard. It's also more affordable in terms of space and money to have multiple voltage standards for comparison rather than multiple calibrators.

[Majorassburn]

Hi. I just joined. I make precision dc references, ac sine wave voltage references, precision resistance references & small linear power supplies especially for DIY calibration needs. If you want to correspond, my email is:  majorassburn@gmail.com and I sell on eBay as SQWARREL. Here's a link or two to some of my listed items:  https://www.ebay.com/itm/285497640527 and https://www.ebay.com/itm/285489340860  and  https://www.ebay.com/itm/285491468993
Please accept my apologies for my amateurish products. I am making them for hobbyists and do-it-yourselfers who want to verify their under-$100 digital multimeters (which I own several ), although I also own a few Fluke 87V's with cal certs.
I have always been fascinated by the fact that no matter how much you are willing to spend on superlative cal equipment, none ever meet your highest expectations! 
I love this forum because it is a VAST source of useful information!

[J-R]

I bought an Advantest R6144 a while back and despite having to beat all the covers back into shape it's quite nice to have around.

I still say having a pile of calibrated references/standards alone is a dead end from a practical perspective.  Then there is the cost of having all the references/standards calibrated.  So the best solution by far is to have one or two of your best DMMs shipped out for calibration, then use those along with non-calibrated sources to check the lesser equipment.

Even a common exception, such as having equipment that only needs a specific calibrated reference becomes questionable once you consider how limited it is along with the calibration cost-effectiveness.

HOWEVER, in the context of a hobby, then of course those things do not matter since we are having fun and doing what we want...


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

[alm]

I still say having a pile of calibrated references/standards alone is a dead end from a practical perspective.  Then there is the cost of having all the references/standards calibrated.  So the best solution by far is to have one or two of your best DMMs shipped out for calibration, then use those along with non-calibrated sources to check the lesser equipment.

I don't disagree but would like to add the following side notes. Having discrete standards like a 10 VDC standard is most useful if you have a way to transfer this 10 V DC to other values like 100 V, 1 V, 100 mV etc. This is how cal labs used to do it (look at Fluke 7105 which used just a 1.018V Weston Cell to calibrate any DCV value from 10 mV to 1000V. This is still how standards labs do it since their primary standards like Josephson Voltage Standards can't generate all voltages they need. So you would only calibrate a single 10 VDC standard. You might want to have multiple so you can estimate how much they're drifting, but you can have one calibrated and compare the others to that one. Same with resistance. Like I wrote, AC is more problematic. So your pile of standards might boil down to 4x 10 VDC and 4x 10 kOhm.

Obviously this is a lot more work than sending a DMM for calibration. It depends on if you have more time or money to spend. Buying / making a standard and tools like a voltage divider can be cheaper, and the voltage standard can be calibrated using a cal club or a budy with a calibrated DMM. Having your DMM calibrated by a buddy however depends on having another calibrated device (like another DMM) and signals for all the ranges (e. g. 100 mV-1000V DC, 100 Ohm - 10 MOhm, etc). So that for most people requires sending out the meter every year or so, incurring a recurring cost. But obviously if you're a professional needing uncertainties down to say 20 ppm, this is the way to go.

[Majorassburn]

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.

[Majorassburn]

One other thought: Actually, a question:

It is my observation that most newer-manufactured "quality" (cough-cough) Chinese, under-$100 DMM's use a single-DMM-chip with true-rms conversion done internally.

I have noticed that their t-rms readings are reasonably accurate on sub-1KHz sine wave and triangle wave inputs but are considerably less accurate with same-frequency square wave inputs.

My suspicion is that their t-rms converter circuitry is optimized for (low crest factor) sine waves to make good marketing specs but that they rapidly fall short when presented with distorted or higher crest factor inputs.

Although I understand that a so-called perfect square wave has a crest factor of 1, it appears that these t-rms circuits don't work well unless they see more easily calculated and converted sine waves.

Has anyone else noticed this "feature" in these newer import DMM's? Thanks.

[bdunham7]

I have noticed that their t-rms readings are reasonably accurate on sub-1KHz sine wave and triangle wave inputs but are considerably less accurate with same-frequency square wave inputs.

My suspicion is that their t-rms converter circuitry is optimized for (low crest factor) sine waves to make good marketing specs but that they rapidly fall short when presented with distorted or higher crest factor inputs.

Although I understand that a so-called perfect square wave has a crest factor of 1, it appears that these t-rms circuits don't work well unless they see more easily calculated and converted sine waves.

Has anyone else noticed this "feature" in these newer import DMM's? Thanks.

It isn't just ultra-cheap or low end products, it is anything with a low-bandwidth (typically on-chip) TRMS converter.  These are primarily designed to be used with mains-derived AC voltages of 50/60Hz.  It is a BW issue, not crest factor, although these same meters will struggle with high CF signals as well simply because anything with a high CF will typically have harmonics well above the fundamental.

A quick test on a Fluke 116 shows me that 5.000VAC (sine) @ 1kHz gives me a reading of exactly 5.000, but a square wave of the same V_RMS and 1kHz gives me 4.880 with about 10 digits of flicker.  Reducing the fundamental frequency improves the square wave performance considerably.  At 60Hz, the difference is only 2-3 counts of flicker with the square wave which indicates that for mains systems, the TRMS function is accurate and useful to the extent you need TRMS at all.

[Mickle T.]

The only reason why Chinese DMM front-end chips have a True-RMS bandwidth limitation of about 1 kHz is that they do not use analog conversion, but mathematical processing of samples from a relatively slow sigma-delta ADC by a relatively fast microcontroller. At least all SDIC Microelectronics solutions have this architecture.

[Kleinstein]

There are DMM chip sets that include digital RMS with a relatively slow SD ADC. This comes with the rather limited BW, but it also comes with positive sides:
The most obvious is the fast reaction: remove the probes from an AC signal and one gets 1 in between reading and than a solid zero. Analog RMS may need a few seconds.
Another point is good linearity also down to low values, like 1% or even less, where analog RMS often does not work well, though the limited resolution still hits.
A final point is the performance with lower frequencies and non sine waveform, like 30 Hz - because of compromise with settling the performance of analog RMS often suffers below some 40 Hz.

A square wave is tricky for many meters. Besides the higher frequency content, there can also be slow rate issues, e.g. at an electronic rectifier. So while it is easy to generate a square wave of known amplitude it is not a great test signal for a DMM. I would add a reasonable know (e.g. calculate with Spice) low pass filter to reduce the highest frequencies (e.g. > 1 kHz) and the slew rate. As there is anyway not that much power in the higher harmoncis the accuracy of the filter is not that critical.

[J-R]

alm, I think we are somewhat agreeing.  I do have some 10V references (among others) and they are great to have for the hobby.  But still there are a mountain of calibration points on a typical DMM, such as the previously mentioned AC but also quite a few for resistance, capacitance, and frequency.  I have multiple ways to generate these inputs, but mostly only by verifying with another calibrated DMM.  I've repaired about a dozen bench meters and they frequently have completely different calibration points.  So simply adding one more DMM to your bench could require another pile of references (even considering the tools you mentioned).

Awesome14/Kaysert, is that you?

[alm]

alm, I think we are somewhat agreeing.  I do have some 10V references (among others) and they are great to have for the hobby.  But still there are a mountain of calibration points on a typical DMM, such as the previously mentioned AC but also quite a few for resistance, capacitance, and frequency.  I have multiple ways to generate these inputs, but mostly only by verifying with another calibrated DMM.  I've repaired about a dozen bench meters and they frequently have completely different calibration points.  So simply adding one more DMM to your bench could require another pile of references (even considering the tools you mentioned).

No, the important point that using the techniques I described, you can generate DC voltages from 100 mV to 1000V using just a stable adjustable voltage source and a 10 VDC standard. The 10 VDC standard is the only thing that needs calibration. Not a "pile of standards". You can do something similar with resistors and AC voltage, and by extension DC and AC current. Frequency is also easy to divide. I think there are similar tricks for capacitance using ratio transformers, but I've never looked into that. There are commercial devices that use this exact principle to adjust themselves from a few artifact standards (Fluke 57xx). Before this people in cal labs used to do it by hand (the Fluke 7105B system I mentioned above).

If you want to calibrate one DMM using another DMM of reference, you still need those adjustable, stable voltages, resistances, currents etc from 100 mV to 1000V. The difference is that you don't need the 10 VDC reference or any ratio devices, and that it saves time in exchange for paying more money.

[mawyatt]

A square wave is tricky for many meters. Besides the higher frequency content, there can also be slow rate issues, e.g. at an electronic rectifier. So while it is easy to generate a square wave of known amplitude it is not a great test signal for a DMM. I would add a reasonable know (e.g. calculate with Spice) low pass filter to reduce the highest frequencies (e.g. > 1 kHz) and the slew rate. As there is anyway not that much power in the higher harmoncis the accuracy of the filter is not that critical.

While we agree the squarewave may be tricky for some meters, and is the simplest of all waveforms, outside DC, to create accurately, very accurately actually. However from the user perspective and actual use, this is where we respectfully disagree.

First off, the user can create an extremely accurate waveform with some simple CMOS logic and an accurate DC reference, without the need for anything other than an known accurate DC meter to measure the DC reference voltage, say 5.000V for example. By design the relative accuracy of the waveform can be inferred to a high degree of precision and confidence, and tightly referenced to the accurate DC reference as the result is simply Vref/2 for the squarewave amplitude. The waveform has a unique property that no other waveform posses other than DC, the Average and RMS are the exact same, precisely Vref/2!!

Secondly, filtering the waveform to slow the slew rate and reduce the harmonics is exactly what one SHOULD NOT do. Since this very effort relaxes the DC reference voltage and the waveform Average and RMS precise 1/2 relationship to said reference.

Since the squarewave is comprised of only odd harmonics that fall of at a rate of 1/n for voltage, power rate 1/(n^2), where n is the harmonic, by filtering the waveform one is throwing away energy in these odd harmonics so the meter can't attempt to record such and thus producing an associated reading error by ignoring or attenuating these harmonics. One must remember that "RMS" is the overall "Heating" effect of all aspects of the waveform, DC, harmonics and such. By utilizing a low frequency waveform, not using any low pass filtering, this places many of the higher frequency harmonics within the meters' bandwidth and thus are recorded, certainly better than just throwing away or purposely attenuating those harmonics.

We've utilized this technique with VDD reference 5.000V for a buffered CMOS Flip-Flop (at low frequency to assure squarewave symmetry), with excellent results awhile ago, and still utilize such to compare various higher end DMMs (3 KS34465A, DMM6500, HP34401A, AG34401A, DMM3065X).

This simply works, and works quite well indeed 

https://www.eevblog.com/forum/testgear/ac-rms-dmm-tests/

The sine wave is certainly a better test and calibration waveform and why it's used by cal labs. However, creating a pure sinewave at precision levels acceptable for DMM comparison/use is difficult and expensive and why most users don't have direct access to this level of expensive equipment.

Here's where the simple CMOS squarewave technique can offer users a alternative at a very modest cost, even attractive for hobbiest

Anyway, hope this clarifies some of the subtle parameters and effects of the simple squarewave for consideration as an RMS reference waveform. We can offer more details, but don't want to detract this thread unless folks are interested.

Best,   

[tggzzz]

Cheap sanity check for generating audio sine waves with a known amplitude...

• Take a 10MHz DDS function generator, quality of your choosing
• Generate a 0.05Hz sine wave
• Attach a DVM which captures min and max readings, set it to DC volts on the fastest sampling rate. I use an Agilent 34410A
• The min and max readings correspond to the peaks and troughs, so calculating Vpp and Vrms is easy
• Increase the DDS output frequency and assume that the Vpp is unchanged. That shouldn't be a problem if the frequency is a few orders of magnitude below its max frequency

[Kleinstein]

I fully agree that the square wave can be created rather accurately. The problem is however that there is a good chance that a DMM may have problems with exactly that square wave shape, especially the high slew rate part. Even an other wise well working AC RMS part may fail under this condition and show a reading that is off a little. This makes the square wave with sharp transitions not suitable for any electronic RMS circuit - it would be only OK for an unbuffered thermal converter.

Filtering will effect the RMS value, but not that much if the cross over is significantly higher (e.g. > 10 x the frequency). A simple filter (e.g. 2nd order passive RC) can be calculated reasonable well. It takes a little math to get the correction factor of some 0.995. There is some uncertainty in that factor, but one can at least estimate it reasonably well, e.g. from the part tolerances and assumed parasitics.
There is nothing bad in having a calculated factor, even if it is not a simple one like 1/2 that can be done in the head.

A know filter is way better than BW limit of the DUT with a usually not well defined BW limit. The BW specs of the meters are usually minimal values and for testing a meter one should rely as little as possible on the quality of the meter.  A nasty point here is that with the usual AD637 and similar analog RMS chips the BW limit is known to be amplitude dependent - that larger the amplitude the faster. Ideally there is a lower BW limit in front, but when aiming for high BW this may be skiped.
Another point are possible slew rate limits and zero crossing delays in the active rectifier. So it is not just the frequnecies, but also possibly additional (nonlinear) effects from the sharp edges.
This alone makes a square wave a poor test signal for amplitude accuracy. It would be more like an extra test - good to pass, but a meter could still be useful if it does not work well with a square wave.

For checking the frequency response of the DMM the square wave is anyway not suitable as a mix of frequencies - this is more a thing to use a DDS type sine generator.

For the lower frequency end (e.g. 10-50 Hz)  it may be interesting to check how the meter reacts to both a more sqare wave and sine wave. However this is beyond the normal tests done, though it is known that the analog RMS chips have some problems at low frequencies that depends on the waveform. AFAIK there are no esteblished test methods for this.

[IanJ]

I'd think having a PDVS2mini would negate the need for the Analogic, at least from a practical perspective.  But there is the cost and stock issue.  It could be 6 months or more before they are back in stock, although now that Ian retired, maybe he'll be faster to get the next batch out!  1,000% recommended, though.

Down to costs rather than time. Some components are still through the roof or not available yet.

Ian

[mawyatt]

I fully agree that the square wave can be created rather accurately. The problem is however that there is a good chance that a DMM may have problems with exactly that square wave shape, especially the high slew rate part. Even an other wise well working AC RMS part may fail under this condition and show a reading that is off a little. This makes the square wave with sharp transitions not suitable for any electronic RMS circuit - it would be only OK for an unbuffered thermal converter.

Filtering will effect the RMS value, but not that much if the cross over is significantly higher (e.g. > 10 x the frequency). A simple filter (e.g. 2nd order passive RC) can be calculated reasonable well. It takes a little math to get the correction factor of some 0.995. There is some uncertainty in that factor, but one can at least estimate it reasonably well, e.g. from the part tolerances and assumed parasitics.
There is nothing bad in having a calculated factor, even if it is not a simple one like 1/2 that can be done in the head.

A know filter is way better than BW limit of the DUT with a usually not well defined BW limit. The BW specs of the meters are usually minimal values and for testing a meter one should rely as little as possible on the quality of the meter.  A nasty point here is that with the usual AD637 and similar analog RMS chips the BW limit is known to be amplitude dependent - that larger the amplitude the faster. Ideally there is a lower BW limit in front, but when aiming for high BW this may be skiped.
Another point are possible slew rate limits and zero crossing delays in the active rectifier. So it is not just the frequnecies, but also possibly additional (nonlinear) effects from the sharp edges.
This alone makes a square wave a poor test signal for amplitude accuracy. It would be more like an extra test - good to pass, but a meter could still be useful if it does not work well with a square wave.

For checking the frequency response of the DMM the square wave is anyway not suitable as a mix of frequencies - this is more a thing to use a DDS type sine generator.

For the lower frequency end (e.g. 10-50 Hz)  it may be interesting to check how the meter reacts to both a more sqare wave and sine wave. However this is beyond the normal tests done, though it is known that the analog RMS chips have some problems at low frequencies that depends on the waveform. AFAIK there are no esteblished test methods for this.

Just for fun, we turned on a few of our DMM meters and gathered our handhelds, an almost 3 decade old Fluke 87, a Keysight UL233A and a Uni-T UT210E for a quick-n-dirty test.

Using our DIY DMM Tester mentioned above set at 250Hz, and without letting the instruments even warm up, or even taking the time to let the plug-in stabilize, just simple Plug-N-Play as quick as possible!!!

DMM                       Vref in volts                        Vac(rms) in volts
Fluke 87                  5.00                                   2.506
KS UL233A              5.000                                 2.509
Uni-T UT210E          4.99                                   2.45
SDM3065X              5.00079                             2.49789
AG34401A              5.00078                              2.49997
DMM6500               5.00090                              2.49995
KS34465A (new)     5.00088                              2.50009
KS34465A (1.5yr)   5.00087                              2.49988
KS34465A (3yr)      5.00088                              2.50019

So we must have some "Magic Squarewaves" then 

Would be interesting to see how well this works with an HP3458A. Maybe Dr. Frank is listening and might consider this with his nice HP3458A, he certainly knows this instrument, the various AC modes, and how to properly apply such!!

Anyway, as always, YMMV 

Best,

[bdunham7]

Here's where the simple CMOS squarewave technique can offer users a alternative at a very modest cost, even attractive for hobbiest

If the hobbyist has meter with capacitor-blocked front-ends for the AC ranges and BW orders of magnitude above the fundamental of your square wave, then your DC-derived square wave is good enough for a "not broken, hasn't drifted" verification test and may even be quite precise.  However, if the hobbyist has any variety of budget DMM that doesn't work well with square waves, especially one-sided ones, your technique becomes less attractive.  The person that started this conversation claims to sell a product that puts out a clean sine wave of 6.000V +/- 2mV.  For a 6600-count DMM, that seems like a better choice for verification.

Would be interesting to see how well this works with an HP3458A.

You would expect any good TRMS, AC-blocked and high BW meter to accurately indicate the AC component of your square wave.  The whole reason you have them is to be able to read the TRMS value of complex signals.  However, if you don't have all three of those characteristics--TRMS, AC-block, high BW--the sine wave will be accurately read but your square wave will not.  You can see your UNI-T is starting to struggle at 250Hz already.

[mawyatt]

Yeah, was kinda surprised how well the old Fluke 87 behaved, and the relative cheap KS UL233A (was part of KS promotion that was "given" away with the purchase of a KS34465A back when we got our 1st 34465A (Tan case), well before the 34465A became seriously backordered). Even the ultra cheap Uni-T didn't do so bad!!

Agree, the 6V +-2mv clean sinewave is a better waveform for this application, IF this is verifiable, stable and repeatable performance!! With all due respect, don't think that what Mr Majorassburn has divulged would stand up well against higher end DMMs in that respect, however he stated that's not the intended audience!

We do know the squarewave concept is extremely stable, doesn't depend on any precision components, nor calibration except reading the DC reference value, then simply divide by 2. Of course if one wants to dive into the intricate details of trapezoidal waveforms which include finite non-equal Rise Fall times and asymmetry, then a "fudge" factor can be applied. A deeper dive which includes exponential Rise and Fall characteristics gets even more interesting!!

However, all this aside, think we've shown it works pretty well, without the need complex setups, stabilization, "fudge" factors and such, at least with the various types of DMMs we own.

Would be very interesting to see what other folks find wrt this squarewave concept.

Best

[mawyatt]

Would be interesting to see how well this works with an HP3458A.

You would expect any good TRMS, AC-blocked and high BW meter to accurately indicate the AC component of your square wave.  The whole reason you have them is to be able to read the TRMS value of complex signals.  However, if you don't have all three of those characteristics--TRMS, AC-block, high BW--the sine wave will be accurately read but your square wave will not.  You can see your UNI-T is starting to struggle at 250Hz already.

Exactly, this would likely revel the intricate details of the waveform rather that the reverse where the waveform revels the limitations of the meter!! Wish we had a 3458A, but have no justifiable use for such an exceptional instrument, can't even conjure up an "excuse" 

Maybe in our next life we'll get one....more likely we'll end up with a very hot broken Simpson or Triplett to measure burning hot coal

Best,

[alm]

Would be very interesting to see what other folks find wrt this squarewave concept.

If only there would have been another topic where the same solution and problems with it were already discussed by the same people.

[Majorassburn]

Agree, the 6V +-2mv clean sinewave is a better waveform for this application, IF this is verifiable, stable and repeatable performance!! With all due respect, don't think that what Mr Majorassburn has divulged would stand up well against higher end DMMs in that respect, however he stated that's not the intended audience!

Hi, again. I love these types of discussions because they remind me that there is no simple answer to any particular need when it comes to electronics! Everything is a compromise of some sort. That's why I enjoy making my amateurish calibrators. Basically, they accomplish a simple purpose, albeit not very well, but at very low cost.

As for my AC Pure Sine Wave generator modules, I have tried 555 & 4047-based square-wave-to-sine-wave generators using phase shift & integrator schemes. Both work well as crude "Yup, your DMM seems to work OK" verifiers. The perfect square wave is one trick to master and the conversion technique to sine wave output has its own problems to address.

One of my challenges   is to end up with minimal-count, low-cost componentry that achieves reasonably repeatable, clean & stable output sine waves. Of course, predictable, repeated, accurate amplitude hinges on  the power supply because the amplitude varies with power supply levels. Refining & decoupling that requires additional circuitry that raises costs to where there is no market other than the occasional curiosity-seeker.

So, I concentrated on a generation technique where I use an op-amp square wave generator to feed the first integrator whose triangle wave output becomes a sine wave out of the second integrator & then buffer/amplify that for the 6V+ sine wave. Lots of distortion but t-rms DMM's don't seem to choke on that!

Also, selecting 50-60Hz generator frequencies results in too much output fluctuation (+/- 5mV) caused by environmental influences & shielding is not an affordable option. So, I use 100Hz as a compromise that results in a nice, non-fluctuating output.

However, the predictable & useful 6VACrms amplitude wholly depends on a controlled power source & the most affordable option is a 12V regulator IC on board. That works good enough for my intended audience because, netting out all the positve and negative tempco's of all the various components used, my module produces a +/- 2mV amplitude predicatbility after warmup in a controlled environment on the 32nd day of the month when the moon is full! 

I would encourage one of you professionals to try one & put it to the test & report the results for all of our benefit. I lack the required test equipment to do any such thing but would love to see whether my modules are any good so I can raise my selling price if they are! 

Finally, the reason I started making the AC sine wave DIY modules is that, short of owning a rather expensive function generator, there doesn;t seem to be a quick & dirty way to get a high enough amplitude, low frequency sine wave to reasonably & accurately get a stable, non-fluctuating reading from a DMM.

Now, go easy on me  ....remember, I'm just an old geezer AMATEUR! 

[bdunham7]

triangle wave output becomes a sine wave out of the second integrator

Well, not quite but perhaps close enough...

[Majorassburn]

triangle wave output becomes a sine wave out of the second integrator

Well, not quite but perhaps close enough...

Thanks. Actual output:

[Gyro]

A small suggestion for your ebay listings, I've no problem with your modest accuracy claims, but you could do with loosing the "Top Quality Double-Sided Fibreglass FR4 PC Board" label in the images. We can all see that it is ordinary FR4 proto board, nothing wrong with that form of construction for a modest spec device, especially when done neatly. It probably puts some of us in mind of a certain controversial 10V reference by an ex-member though. He made extravagant / magical claims (2ppm) for a bodged together matrix board,copper foil, and dodgily soldered unit that he still sells on ebay to this day for >$1200 (do a forum search for 'D-105' if you're interested in the sorry tale).

Just a matter of not calling a spade an earth inverting horticultural implement. You don't need it.

[Majorassburn]

to GYRO: "A small suggestion for your ebay listings, I've no problem with your modest accuracy claims, but you could do with loosing the "Top Quality Double-Sided Fibreglass FR4 PC Board" label in the images. We can all see that it is ordinary FR4 proto board, nothing wrong with that form of construction for a modest spec device, especially when done neatly."

DONE!  Thank You for the suggestion.