Ultra Precision Reference LTZ1000

[zlymex]

Where does THY888 sell his units? They look interesting.

He sells most of his stuff at 38hot.net, such as http://bbs.38hot.net/forum.php?mod=viewthread&tid=98892

[zlymex]

https://world.taobao.com/item/522894165585.htm?spm=a312a.7700714.0.0.lqRGB8#detail

"Out of stock" replied by the seller. Obviously a fishing bait.

[lowimpedance]

The bashed up parts are a little worrying. On the one hand it would be great to get a well worn in LTZ1000 but on the other I've read of the people who recover these that they will snip off old legs and spot weld new ones using their cheap crap wire that becomes a load of hotspot thermal junctions and renders the LTZ unfit for purpose? 5.5 digits may be ok

Those weld-legs parts were pretended to be new that my friends and I would never buy. We buy LTZ1000 either new or with original legs and original marking.

An interesting pile there !, what were they sniped from ?.

[zlymex]

Those weld-legs parts were pretended to be new that my friends and I would never buy. We buy LTZ1000 either new or with original legs and original marking.

An interesting pile there !, what were they sniped from ?.

That is the question I've been asking. But all I got is something like these.

[lowimpedance]

Good collection of vishay resistors and other expensive parts on the PCB too !.

[zlymex]

Good collection of vishay resistors and other expensive parts on the PCB too !.

Sorry I didn't make myself clear, I meant " all I got is something like these photos". I don't posses that board. Those photos were coming from a seller of used LTZ1000.

[Kleinstein]

As the LTZ1000 does not really need a controlled temperature, I don't think the extra oven needs to be that stable. If the conditions are not to bad, even a slow, e.g. simple proportional control might be good enough.
It might be interesting to have the option to set the temperatures to a few different values to check for the TC of the circuit inside and maybe get the right value for the 400 K resistor.

The soldering on the temperature control board does not look that good. But the circuit might be good enough. For stability the sensor should be in reasonable contact to the case - so take care when moving it.

[martinr33]

Heater voltage readings for the blue case LTZ1000 reference from TaoBao.

Screened cable connected to the heater electrodes, connected at the diode and the transistor emitter.
Allowed 30 - 60 minutes to stabilize.

Temperature is maybe 22 - 23 c. Can't find my Raytek.

Heater voltage at startup 8.4 volts. Holds there until ref hits temp, then drops quickly.

Test                                              LTZ1000 heater voltage
Hanging in free air, no case             7.78 - 7.80. Blow on it, 7.95. This is why people put foam on the part.
Case only, no case heater               7.353 - millivolt movement over minute or two.
Case with case heater active           5.863  - millivolt movement over a minute  or two

Case heater is about 1.4W (14V 0.1A)

Agree that the case heater doesn't have to be that precise. It is very helpful with all the other parts - there's no temp drift as long as the outside temp is less than the case setting. Plus, the EM shielding is good. Now, as I noted I am still at a suspect 6.5 digits. So this is still junior stuff.

When I pull the heater sense wire, i'll put some thermal goop back in. I'll have to trace the circuit out, see what it takes to calibrate the heater.

[Andreas]

Hello,

update from my measurements on LTZ#3-LTZ#6
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg935102/#msg935102

here the updated table with averaged drift from all measurements and the charts:

I recorded (weekly) readings to determine ageing drift against my ADCs and against LTZ#2 with two 6.5 digit DMMs in 100 mV range.
LTZ#5 was needed most of the time for measurement of the T.C. of the LT1027 references. So there are some gaps in the charts.

Evaluation is from day 128 (after all adjustments done) to day 238 so around 3 kHrs.
The readings indicate all below 2 uV / kHr or below 2 ppm/year compared to my measurement setup.

LTZ#2 drifts about -1.57ppm/year.
the ADCs drift also in the range of 1-2 ppm over one year with some seasonal changes.
All in all there is not much difference in LMS slope between the (absolute) ADC readings and the DMM differential reading.

Up to now LTZ#6 and LTZ#4 seem to be with the least ageing drift.

With best regards

Andreas

[splin]

Andreas,

Are these long term drift tests continuously powered or just powered up for each weekly measurement? Can you provide a link to your current test proceedure - you've done a lot of posts so not easy for me to find the relevant one!

Also could you post spreadsheet data so that we can create a graph for each ADC/DMM showing all four LTZs?

[Andreas]

Hello,

my battery powered references are all running 24/7
Also the battery powered ADCs.
The 6.5 digit DMMs are only running when being used (with >= 2 hrs warm up time).
All ADCs are connected in parallel to the DUT - Reference.
The DMMs are connected between DUT-Reference and LTZ#2 reference.
The HP is running with 100NPLC and the K2000 with 10 NPLC (=maximum) integration time.
The measurement values are averaged over 5 minutes measurement time to reduce noise.
Temperature varies from 20-32 deg C in my "lab" in summer.

With best regards

Andreas

[TiN]

One thing I notice during 4920M service is rather thin PCB substrate for LTZ1000 module.



Seems like it would help for better thermally decoupling of hot LTZ oven from rest of the circuit.
Also nice copper plane right under LTZ location on main A/D board. EMI shielding?

[Andreas]

Hello,

Interesting: the LM399 as auxiliary reference besides the LTZ1000 module.
Don´t they trust the LTZ alone?

With best regards

Andreas

[lowimpedance]

The thin PCB has been used in other Datron equipment, as I found with the ref. module in a 4808. (thickness 0.6mm).
pics here;
https://www.eevblog.com/forum/testgear/datron-voltage-reference-pcb-module-pics/msg813331/#msg813331

[Mickle T.]

1271 uses the same thin PCB too.

[Andreas]

The LT6011 has slightly better specs than the LT1013, and is not that much more expensive.

Mhm:
you will need a negative power supply for the LT6011 (Common mode input range 1.5V above negative rail).
The output current may be marginal for the 5mA current source. (5mA only specified as short cirquit current with 1V overdrive).
Gain is only specified at around 2 mA (5kOhms load) and not at 5 mA (2K Ohms) needed for the current regulator.
I do not know if this is really a upgrade.

With best regards

Andreas

[Galaxyrise]

I will keep looking...

Did you already rule out the actual upgrade of the 1013, the 1413?

[zlymex]

I will keep looking...

Did you already rule out the actual upgrade of the 1013, the 1413?

There is also the LT1213 as well a the LT1413.  I'm going for lower power if I can.  There are some promising parts from Linear Tech and also ADI.  I have not yet checked TI, because their website search tool does not work for me, and I'm trying to find a browser that will work with it.  Still looking...

What about OP727? It's better than LT1013 for many params such as Vos, Ib, Is, PSRR and LF noise.

[zlymex]

......  I'm still having trouble with the TI website (this has been going on for years now-- their website designers should be fired IMHO)...

I found out nothing at TI website if the auto-zero opams such as OPA2188 or OPA2180 are ruled out. The only one near LT1013 is TLE2022BC.

[Andreas]

I think you have overlooked the Burr Brown "equivalent" of the LT1013:  OPA2234

But open loop gain is a factor 7-8 lower.

with best regards

Andreas

[EmmanuelFaure]

In my opinion, the discussion about what op amp to choose spanning all over this topic look exactly like this :
https://en.wikipedia.org/wiki/Law_of_triviality

[Kleinstein]

The LT1013, LT1413, OPA2234 and AD797 and likely some more are well good enough. So there is no real need to look for something better - the 4 types listed are very similar anyway.  From first sight I would expect that even an LM358 would not make a significant difference.

The real points that can matter are the thermal design, lead / wire resistance and the 400 K resistor (not the resistor type but value and position for compensation) for the non A version to compensate the TC. Power dissipation of the OPs is not that critical either: the Reference zener takes some 5 mA and the divider to set the temperature about 0.5 mA.

[Dr. Frank]

...
True-- we are saving only about 600uA in a circuit that uses about 40mA-45mA (including the heater circuit), ..

Which kind a version do you mean?
I use LTZ1000, with external thermal isolation, at 45°C, 12k/1k, LT1013, powered with 12Vdc, standard circuit, plus modifications by Andreas.

The circuit consumes around 50mA initially, but 22mA only when stabilized.
So to which solution relates your 45mA current consumption?

Frank

[Andreas]

Hello,

according to my measurements:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg874560/#msg874560

I have 20-24 mA at room temperature. Even with 3*LTC2057 OpAmps which consume nearly 1 mA each.
So with 12*NiMH AA cells you will have easily 2-3 days of operation even if the cells are somewhat older.

With best regards

Andreas

[Kleinstein]

Even in the compensated circuit, there is something like a 5 mA zener current that is needed to get the low noise. So even than it does not make a big difference if the OPs take 600 µA or 300 µA. One might get away with lower zener current it is only for the good long therm stability and not the LF noise.

If you really needs to go for low noise and low power, there would be the rather crazy way of using a battery (e.g. 7.2 V nominal) as an intermediate reference to provide low noise and use some kind of filtering / adjustment to get the long term stability of the LTZ1000 (that might than run at lower current). So the battery (with companion circuit) as kind of low pass filter in the mHz range.