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5 Digit Accurate Volt Meter

This meter is upgraded to E+.

Just ordered 61E+ This will be an upgrade from my almost 40 year old Fluke 77. I've been borrowing a Fluke 87III meter for 4.5 digit accuracy, which I need to return.

RS232 communication is replaced with USB. Very nice.

Those things seem to be a good value.
 
I used one of these:


Divided the 4.096V output by four using four identical resistors. This used all digits of my 6.5 digit HP 3456A, and a rented 8.5 digit HP 3458A.
The 3456A readout toggled +/- 1 count in least significant digit (+/- 1ppm) of the reading from freshly calibrated 3458A

The 3456A is as old as my career, from the 1980's
 
Hedges, you have a circuit diagram on how to use that IC?

I like to know the offset I need to keep in mind when I use a known voltmeter,
I found one being low by 0.2v
This is all in 0 to 13v range.
 
3 wire vs 2 wire,

I want to install a voltage gauge on my 12 volt batt,

What are the pros/cons of going with either 2 wire vs 3 wire volt meters?
 
Hedges, you have a circuit diagram on how to use that IC?

I like to know the offset I need to keep in mind when I use a known voltmeter,
I found one being low by 0.2v
This is all in 0 to 13v range.

Data sheet shows example circuit. Just voltage source and capacitors. Could use one 9V battery, or specs are better if given more like 18V


I looked for an eval board but didn't see one. Could use an SOIC SURFboard or something like that.
To scale voltage I use multiple identical 0.1% or 0.01% resistors. Consider input impedance of your DMM (some are 10 meg ohm) when selecting values. When I compared two DMM I connected both at once so even if absolute voltage wasn't precise to one ppm, they were measuring the same signal.

A reference like this IC plus zero volt short gives two points to calibrate a meter. For very low voltages (uV), heat flowing through dissimilar metals is an issue. Letting temperature stabilize and reversing polarity could help. Background noise matters, so some meters average over one or more 60 Hz power line cycles.
 
3 wire vs 2 wire,

I want to install a voltage gauge on my 12 volt batt,

What are the pros/cons of going with either 2 wire vs 3 wire volt meters?


Apparently referring to a meter powered by the circuit.
I use handheld or bench instruments powered by AC or battery. They can measure millivolt to 1000V.

If you were trying to measure one cell precisely, wouldn't want voltage drop at contact resistance to affect reading, or or variable power supply voltage, so use an instrument.
Avoiding contact resistance would need 4-wire not 3-wire. And it still loads the circuit.

I guess these circuit powered panel meters might be installed in a system to monitor it.

Monitoring a 12V battery, you're in the voltage range of a panel meter and accuracy isn't that important. 2-wire would be fine. If you get 3-wire, then you can move it from battery to measuring other voltages (but only relative to negative.) That could be useful to measure connections between cells.
 
Building a reliable and accurate voltage reference is not a trivial task - even if you have the schematic.
Ask me how I know.

If you only need ballpark accuracy, maybe. But then again, nearly any meter will already give you ballpark accuracy even if it is crappy and old.
 
Building a reliable and accurate voltage reference is not a trivial task - even if you have the schematic.
Ask me how I know.

If you only need ballpark accuracy, maybe. But then again, nearly any meter will already give you ballpark accuracy even if it is crappy and old.

In the case of MAX63xx, it's all in an IC.
The schematic is just showing voltage in and decoupling capacitor.
With that battery powered and held at room temperature, should give a reference that is stable to a couple ppm. Far better than most crappy to moderate quality DMM.

With ICs delivering performance as good as 1 ppm/degree C, that much is relatively easy. Better than that is what gets difficult; you need to do oven control, otherwise something more exotic. I used the Maxim part in several of my boards. For one board I oven controlled it.

My 3456A like most ppm level DMM uses a TI voltage reference that comes packaged with a heater for roll-your-own oven control. If you can keep its 1 ppm/degree reference within 1 degree C while ambient varies 20 degrees, system performance is 0.05 ppm/degree. But I think the newer 3458A's spec required 2 degree environmental control to guarantee 1 ppm accuracy.

"Even though precision sub-1-ppm components such as the AD5791 are available on the market, building a 1-ppm system is not a task that should be taken lightly or rushed into."


Yet that is what I was asked to do. With programmable voltage to about 80V.
My breadboard achieved about +/- 10ppm over +/- 10 degrees C, a 1.0 ppm/degree result.
Fools rush in ...

Redneck thermal chamber.jpg
Redneck thermal chamber (because the company purchased our recommended chamber for the Bangalore team, not for us.)
 
In the case of MAX63xx, it's all in an IC.
The schematic is just showing voltage in and decoupling capacitor.
With that battery powered and held at room temperature, should give a reference that is stable to a couple ppm. Far better than most crappy to moderate quality DMM.
Couple of ppm stability for short-term. "typical" 30ppm/1000h long term stability and manufacturer datasheet "typical" figures are often pretty wishfull thinking. Also 20ppm thermal hysteresis after 25 degree step. Humidity not specified but often lot more than you'd want. (not suprisingly all high precision references are in hermetic casing instead of plastic)

10ppm per year gets to sorcery that makes snake-oil hi-fi look credible. :p

LTZ1000 buried zener reference is still the "gold standard" even after 30 years.

Oops, drifted to volt-nuts territory.
 
Couple of ppm stability for short-term. "typical" 30ppm/1000h long term stability and manufacturer datasheet "typical" figures are often pretty wishfull thinking. Also 20ppm thermal hysteresis after 25 degree step. Humidity not specified but often lot more than you'd want. (not suprisingly all high precision references are in hermetic casing instead of plastic)

10ppm per year gets to sorcery that makes snake-oil hi-fi look credible. :p

LTZ1000 buried zener reference is still the "gold standard" even after 30 years.

Oops, drifted to volt-nuts territory.
Yes.
Yes.
Yes.
Yes.

With all of this said.....the battery and BMS world does not get much benefit from volt-nuttery.
It is the realm of ultra-senstive sensors, semiconductor characterization, etc.

Sure is a fun rabbit hole for hobbyists though. And a rabbit hole it is. Next thing you know is you are trying to hide the expense of an Agilent 3458A 8.5 digit DMM and the other one for parts from your spouse. "But baby, I need to get it calibrated to properly characterize the bus bars on our battery bank"
 
Sure is a fun rabbit hole for hobbyists though. And a rabbit hole it is. Next thing you know is you are trying to hide the expense of an Agilent 3458A 8.5 digit DMM and the other one for parts from your spouse. "But baby, I need to get it calibrated to properly characterize the bus bars on our battery bank"

We keep "His", "Hers", "Ours" accounts.
She counts pennies. I count decimal places. (Prices pretty much form a Pareto diagram that way.)

Because my boxes are so big, hidings the parts units is difficult.
 

Apparently referring to a meter powered by the circuit.
I use handheld or bench instruments powered by AC or battery. They can measure millivolt to 1000V.

If you were trying to measure one cell precisely, wouldn't want voltage drop at contact resistance to affect reading, or or variable power supply voltage, so use an instrument.
Avoiding contact resistance would need 4-wire not 3-wire. And it still loads the circuit.

I guess these circuit powered panel meters might be installed in a system to monitor it.

Monitoring a 12V battery, you're in the voltage range of a panel meter and accuracy isn't that important. 2-wire would be fine. If you get 3-wire, then you can move it from battery to measuring other voltages (but only relative to negative.) That could be useful to measure connections between cells.
Gotcha,

Well, for my bigazz cells, they are the ONLY source of power, so I guess 2 or 3 pin is a moot point.

Voltage sagging - the meters should not affect the displayed voltage due to their draw.
I plan on using one of these on a buck/boost converter to watch the output.
 
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