Andreas are you referring to this board?
http://www.maxmcarter.com/vref/And btw...does anyone have any pictures or schematics of the high precision version of the HP3458A reference board?
- Simon
Yes, thats it.
I do not believe that the high precision version differs from a standard version.
Except that the pre-ageing of the reference at the facility has been either done for a longer time
or by selecting the better boards.
With best regards
Andreas
Hello,
now after about 1500 hours the LM399 CH6 + CH7 seem to stabilize.
So I plan to repeat the tilt measurements.
With best regards
Andreas
What a bummer, Dave would say. LM399 CH7 is drifting incredibly and hasn't stopped yet even if it seems to settle to smaller drift rates.
Is it just a variance or is there a correlation to the lead lengths? Your guess is as good as mine, but would be interesting to investigate
Just to clarify:
lead length is the same (short leads) for CH6 + CH7.
CH7 uses a slotted board area.
CH6 uses non slotted board.
But I do not think that this has directly something to do with ageing drift.
with best regards
Andreas
Let me take the role of the "Bild" Newspaper:
SLOTS IN PCB INCREASE AGING DRIFT
Effect discovered by amateur scientist contradicts prior scientific work considering slots to be advantageous. We all gonna die!
Let me take the role of the "Bild" Newspaper:
SLOTS IN PCB INCREASE AGING DRIFT
Effect discovered by amateur scientist contradicts prior scientific work considering slots to be advantageous. We all gonna die!
Don't, there are people out there that could believe in that, see below.
One exemplar is not of statistical relevance, thats for sure.So, it seems that the slots are counter productive in this use case. Maybe, it would be better to let your LM399(s) be on a separate PCB from the rest of the circuitry. That would make the whole LM399 assembly easier to insulate.
No, there is no significant number of examples that proof such an argument. It was just a loud thought of mine, but this larger drift of one exemplar could be nearly everthing and is not constrained by an effect of slots in the board. Maybe I should delete my thought in my previous post? Damn.
Has anyone an information about the temperature stability of the thermal regulator inside the LM399 ?
This is a possible question to Bob Dobkin ...
Regards,
macfly
Hello macfly,
not so good as in the LTZ1000.
you can see this in my tilting experiment.
https://www.eevblog.com/forum/projects/lm399-based-10-v-reference/msg360779/#msg360779
Further the stability is dependant on heater supply voltage.
You can get good results with stabilized heater voltage and good thermal management.
With best regards
Andreas
Hello Andreas,
very interesting, but not really an answer of my question. But I asked with some thought's unspoken.
Yesterday, I tested my 5 pieces of LM399H in a manner, I have not read anywhere:
1. Supply the zener with ~1mA - but do NOT supply the heater.
2. Measure the output voltage
3. Put the heater on, wait for thermal balance.
4. Then re-adjust the zener current, to get rid of the zener's dynamic resistance.
5. Measure ouput voltage again.
With these two measurements you may approximately calculate the temperature coeffcient of the device.
If we assume ~90°C working temperature with a stability of +/-0.1 degrees Celsius, the best of my LM399
has a temperature coefficient of only ~0.06ppm/°C.
Now you understand my first question about the stability of the regulation?
I was very astonished about these result.
Regards,
macfly
Now you understand my first question about the stability of the regulation?
Hello macfly
Not really. (how are the exact measurement conditions and what do you mean when speaking of temperature coefficient).
The unheated reference should be in the around 50ppm/K range. (Similar to the LTZ1000).
The heated reference near room temperature is much better.
On my LM399#2 i measured 8uV maximum voltage difference (including hysteresis + noise) in a range of 8-46 degrees celsius environment temperature (measured outside the card box). Note: the voltage (right y-axis) is measured as difference in mV between 2 LM399 references. One at room temperature the other within a "thermal chamber".
So the temperature "coefficient" according to "box method" would be 0.008mV / 6860 mV / (38 K) = +/- 0.015ppm/K.
The temperature "slope" is around -0.07ppm/K as best fit straight line.
But most of the measured error is probably due to thermocouples at the solder joints.
Since I get similar results with a LTZ1000 based reference.
With best regards
Andreas
Now you understand my first question about the stability of the regulation?
Hello macfly
Not really. (how are the exact measurement conditions and what do you mean when speaking of temperature coefficient).
The unheated reference should be in the around 50ppm/K range. (Similar to the LTZ1000).
The heated reference near room temperature is much better.
Hello Andreas,
attached you will find my measurement results. What me surprised is, that the tempco (calculated out of the Vz @ 20°C and Vz @ 90°C)
is more then ten times lower than the 50 ppm/K. With my guess of a regulator stability of 0,1K, one of the LM399 has nearly the same tempco
as a LTZ1000 !
Regards,
macfly
I have a very different results of the LM399 TempCo measurements.
Hello macfly,
the results are too good to believe.
That brings me to the idea to select the references according to raw tempco.
I have looked up my measurements: unfortunately I did not document the values carefully.
But the difference of 2 of my references is at least 4-5mV unheated / heated.
@macfly + Mickle:
Did you use National Semiconductor parts or LT parts?
On my side all are National Semiconductor parts up to now.
@macfly:
Did you kelvin sense of the zener or is the heater current affecting the zener voltage?
With best regards
Andreas
It seems that it will be an even better reason for me to follow this thread, my 6.5 digit meter had a 200uv offset at 10 v.
Parts from National Semiconductor with the same date code, kelvin connection.
What are the differences in the H vs. AH specced parts?
That brings me to the idea to select the references according to raw tempco.
Hello,
when thinking twice the better idea would be to test the tempco without heater around 90 degrees.
There is a large possibility that the tempco is not linear but either a parabolic or s-shaped curve (due to compensation of the zener with a Vbe).
So it can be that at 25 degrees and 90 degrees the voltage is accidently the same but in worst case with a large drift around 90 degrees.
It seems that it will be an even better reason for me to follow this thread, my 6.5 digit meter had a 200uv offset at 10 v.
200 uV = 20 ppm is below the 35 ppm/year as in the specification of a good 6.5 digit meter. (Which one is it?)
If it includes the first year drift I would not bother about.
Later the drift should go down to 1-2 ppm / year for a good instrument.
What are the differences in the H vs. AH specced parts?
The A-type is selected for a smaller (overall) tempco and smaller initial tolerance (National Semiconductor only). See datasheet.
With best regards
Andreas
I should have said that there was a 200uv offset between the +\- readings on the 10 v scale, I had to use a 9v battery to get a stable enough reading.
My meter is a Schlumberger Solartron 7065, mine is about 33 years old.
Hello macfly,
the results are too good to believe.
That brings me to the idea to select the references according to raw tempco.
I have looked up my measurements: unfortunately I did not document the values carefully.
But the difference of 2 of my references is at least 4-5mV unheated / heated.
@macfly + Mickle:
Did you use National Semiconductor parts or LT parts?
On my side all are National Semiconductor parts up to now.
@macfly:
Did you kelvin sense of the zener or is the heater current affecting the zener voltage?
With best regards
Andreas
Hello Andreas,
1. ... That brings me to the idea to select the references according to raw tempco -> No - this was my idea
2. ... the results are too good to believe -> yes, they are too good - and that was the reason for my post.
3. ... Did you use National Semiconductor parts or LT parts? -> I used NS parts.
4. ... Did you kelvin sense of the zener or is the heater current affecting the zener voltage? -> For sure.
At weekend I will repeat the measurement.
@Mickle
Thanks for your measurement results - they are just like that, what I expected.
Regards,
macfly
Hello,
I have now modified my LM399 ageing board with 2 jumpers to switch off the heaters.
There are 16 LM399 from National Semiconductors with 2 different datecodes (12 + 4)
Room temperature was 23 deg C so with around 2 K self heating of the 7mW zener I guess 25 deg for the cold value.
The measured values cold + hot are as follows:
With best regards
Andreas
Interesting that the lower TC modules tend to be < 6.9V. Makes me wonder if the others would have a lower temp Co at a lower current.
Interesting that the lower TC modules tend to be < 6.9V. Makes me wonder if the others would have a lower temp Co at a lower current.
Hello,
very good eyes !!!
so the "ideal" voltage on my references seems to be around 6875 mV.
In the ageing cirquit I use simple 6K8 Metal film resistors (#4-11) or 10K + 22K in parallel (#12-19)
along with a 15V low drop regulator.
with best regards
Hello Andreas,
thanks for yur measurement results. This nearly confirms my measurements.
And as Galaxyrise observed, my LM399 with the lowest TC has the lowest Vz.
Next step to do is changing the zener current and looking what happens ....
Regards,
macfly
Somewhat off topic but interesting for all of us. I'm currently looking for precision resistors and here is what I found up to now:
Distributor Resistor type Value Toleranz TC Stability Price
HBE-Shop Y14535K00000V9L 5K 0,005% ± 0,05 ppm/°C to ± 0.005 % at 70 °C, 2000 h at rated power 34,94 €
HBE-Shop Y145320K0000V9L 20k 0,005% ± 0,05 ppm/°C to ± 0.005 % at 70 °C, 2000 h at rated power 37,81 €
HBE-Shop Y00625K00000T0L 5K 0,010% ± 1 ppm/°C ± 0.005 % at 70 °C, 2000 h at rated power 18,44 €
HBE-Shop Y006220K0000T9L 20k 0,010% ± 1 ppm/°C ± 0.005 % at 70 °C, 2000 h at rated power not in stock
HBE-Shop Y07855K00000T9L 5K 0,010% ± 2 ppm/°C to ± 0.005 % at 70 °C, 2000 h at rated power 20,53 €
HBE-Shop Y078520K0000T9L 20k 0,010% ± 2 ppm/°C to ± 0.005 % at 70 °C, 2000 h at rated power 21,14 €
Burster 1142 5k 0,010% ± 2 ppm/°C 0.01% over years 23,13 €
Burster 1142 20k 0,010% ± 2 ppm/°C 0.01% over years 23,13 €
Rohpoint 8G16D 5K 5k 0,100% ± 3 ppm/°C ±35ppm/10,000hours ±50ppm/26,000 hours 4,52 €
Rohpoint 8G16D 20K 20k 0,100% ± 3 ppm/°C ±35ppm/10,000hours ±50ppm/26,000 hours 5,30 €
Rohpoint 8G16A 5K 5k 0,010% ± 3 ppm/°C ±35ppm/10,000hours ±50ppm/26,000 hours 6,80 €
Rohpoint 8G16A 20K 20k 0,010% ± 3 ppm/°C ±35ppm/10,000hours ±50ppm/26,000 hours 7,95 €
The hermetically Vishay types seem to be unobtainium and have long waiting time. Most of the Vishay parts seem to be not in normal stock, a simple of the shelf (these are my words because its standard datasheet value and not custom made) DSMZ divider needs at least 3 months to arrive. Are you guys at Vishay kidding me? For a proof of concept this is much to long and inadmissible. The price is for sure fair:
1-24 pc. 25-49 pc. 50-99 pc.
21,05 € 15,30 € 12,40 €
Someone with other and better resisitor sources out there?