I would guess that the analogue supply is using a sine wave drive, probably at a fair amplitude and able to give a low distortion output. That will give low noise ( aside from the fundamental) and will provide enough power using the simple 2 turn primary and probably a resonant secondary with some fast switches as synchronous rectifiers on the secondary side. 1MHz as a drive looks about right for the size, and you will get a fair power as well.
I think the 21V rails are used for the relay drive, as they probably want to reduce the current in the coils, and a 24V coil will operate reliably with 21V, and still switch fast enough. There must be some switchers on the supply board though, as getting 5V off 21V with a linear regulator will involve some cooking. The converters are probably on the other side of the board, shielded by the transformer shield, and using those large collection of Nichicon and polymer caps as final filtering.
Never thought I would as about Nyquist sampling on a DMM. With a sample rates as high as 1 MSps has any one thought about doing some testing see the frequency performance of the DC measurement. Haha never thought I would as that about a DMM. 18 bits is almost pushing the limits of 32 bit floating point math for a FFT.
Really great tear down! Thank you for that.
Nice to see some German made WIMA capacitors on the board as well.
Now it would be nice to have a side by side comparison between this one and the Keysight 34470A 7 1/2 digit meter.
No way, guys!
Even though Wayne C. Goeke, designer of the HP3458As ADC, is the person to join Keithley, the 7510s ADC by no means comes near the 3458A!
Lay their specs side by side, and you will promptly see a big quality difference, yet.
Its linearity is mediocre 1..2ppm, again, likemostall other 6 1/2 ... 7 1/2 DMMs, and still no other DMM has got this unique , true AUTOCAL function...
Obviously, the true value of this function (i.e., a complete cal lab built inside) is still not clear to everyone...
Frank
Do you know what is the specific feature which take the linearity from 2ppm to 0.2ppm in the ADC?
That 3904 could be used as a temperature sensor. Came across a setup like that when looking at the LTC2990 datasheet, an i2c voltage/current/temperature ic.
Maybe patents still guard these designs.
I just dropped by this thread to ask what that guy is. Never seen a SSOP-80 before. They are calling it "MilliPaQ". Good name. I want one on my project just because it looks cool.
I wonder if it wouldn't be smarter of instead of switching in the voltage-resistor combos with JFETs to switch current into the integrator.
I wonder if it wouldn't be smarter of instead of switching in the voltage-resistor combos with JFETs to switch current into the integrator.Keithley 2002, Prema 6048, Advantest 6581 and many other DMMs do the same thing.
Dave mention it's 18-bit ADC, but I remember Keithley marketing materials says 32-bit? Can find source yet, but somehow that stick into my mind.
Custom 32bit Keithley special for slow measurements, 18bit AD7982 for faster readings.
I actually spy two AD7982's on the board.
Those 18 bit 1MSPS AD7982s aren't cheap devices at approx $23 each @ 1K. Anyone got the faintest idea why they would have 2 of them?
I can't think of any good reason - they *could* use them to provide full rate 1MSPS digitizing with alternating autozero and gain calibration to avoid drift during long sampling runs but it seems very unlikely. In any case they could have used a single 2MSPS 18 bit AD7641 at $29. Also the manuals/specs don't suggest it does this.
I can't think of any good reason - they *could* use them to provide full rate 1MSPS digitizing with alternating autozero and gain calibration to avoid drift during long sampling runs but it seems very unlikely. In any case they could have used a single 2MSPS 18 bit AD7641 at $29. Also the manuals/specs don't suggest it does this.
Multislope converters want to know where approximately the slope is, to avoid saturation during run up and keep run down times small ... so they could be using one of them for that.
Dave mention it's 18-bit ADC, but I remember Keithley marketing materials says 32-bit? Can find source yet, but somehow that stick into my mind.
Custom 32bit Keithley special for slow measurements, 18bit AD7982 for faster readings.
I actually spy two AD7982's on the board.
Those 18 bit 1MSPS AD7982s aren't cheap devices at approx $23 each @ 1K. Anyone got the faintest idea why they would have 2 of them?
I can't think of any good reason - they *could* use them to provide full rate 1MSPS digitizing with alternating autozero and gain calibration to avoid drift during long sampling runs but it seems very unlikely. In any case they could have used a single 2MSPS 18 bit AD7641 at $29. Also the manuals/specs don't suggest it does this.
Those 18 bit 1MSPS AD7982s aren't cheap devices at approx $23 each @ 1K. Anyone got the faintest idea why they would have 2 of them?
I can't think of any good reason - they *could* use them to provide full rate 1MSPS digitizing with alternating autozero and gain calibration to avoid drift during long sampling runs but it seems very unlikely. In any case they could have used a single 2MSPS 18 bit AD7641 at $29. Also the manuals/specs don't suggest it does this.Probably to have overlapped measurement/calibration cycles.
Driving high speed accurate ADCs is a real task, and you cannot switch every other measurement. Settling time of 0.5uS 5V with 18 bits, and to have anti-aliasing filtering... well that is a bunch of high speed amplifiers (fairly precision) after each other.
Interesting comparisons Keysight 34470A with Keithley DMM7510 http://imgur.com/gallery/Wbx7q
VI. DESIGN FOR ISOLATION
The back-to-back calibration configuration is shown in Fig. 3 and inspection shows that if the power supplies generate common mode current, this will flow through the sense resistor. It, therefore, constitutes an error if it is dc or a disturbance if it is AC. A new dc–dc converter using a patented double-screened transformer construction was chosen, together with a slew-limited low-noise switching controller. This ensures that there will be no difference between use with external power supplied and use with the external supply completely disconnected when under battery power. The double-screened transformer uses two toroidal cores, independently wound, one each for primary and for secondary. Each is fully screened within injection moulded conductive plastic shrouds and coupled with an external “shorted turn” winding around both cores. The resulting coupling capacitance from primary winding to secondary screen is less than 0.1 pF and in use 10 nA of pk-pk AC coupling current is achieved compared with at least 1000 times more in most commercial units.
......
The white (ceramic ?) collar you see around the LTFLU, seems to be the exterior heater, it's named 'H2', obviously.
Its temperature might be controlled by the 2nd OpAmp , maybe.
The plastic or metallic shield around the whole assembly, also the one on the bottom side, also serve as a thermal isolation, so that the whole interior may heat up .. there's a LM35D temperature sensor also, maybe to measure if the whole assembly has been stabilized.
On the bottom side, I assume that there are 4 stable, (leaded?) resistors, which are always needed for the topology of this Reference Amplifier, aka LTFLU / SZA263 / T.I. device from all Fluke calibrators and voltage standards.