Electronics > Metrology

ADR1399 reference

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ivo:

--- Quote from: iMo on November 17, 2023, 03:11:45 pm ---Is there any recommendation what type of the 1uF (ser 5R1) output capacitor should be used?
Foil or MLCC?

--- End quote ---

It's a 1uF good MLCC + 5.1R resistor, AFAIK essentially to emulate a tantalum cap, same with older regulators wanting tants/ECs to settle on their output pin and you can generally pull the same trick with them

In the LM399 datasheets they advise you can do a similar thing with the heater: you can add 10~500R above it to limit the current draw on initial heatup, but to do so you must add a 2.2uF *tantulum* cap across it.


--- Quote from: dietert1 on November 21, 2023, 05:44:21 pm ---Trying to save a 1 cent part on a 15 $ reference?

--- End quote ---

My guess is because people don't want to have to deal with production scale soldering polypropylene (can't stand up to high soak temps) if they don't have to, and prefer to save cost on a tant. And yes two 1 cent parts vs a 10-50c part is a big difference!

Andreas:
Hello,

update from ADR1399 PCB#2 now at 3 kHrs for the metal can devices (KHZ) and 3.1 kHrs for the LS8 devices (first 100 hours not shown):

See also
https://www.eevblog.com/forum/metrology/adr1399-reference/msg5145858/#msg5145858

The values are all temperature compensated (temperature sensor at the bottom of the hammond die cast housing)
Now the LS8 devices, which started with negative slope for ageing, trend to a slow upwards ageing slope like the TO-46 metal can devices.

with best regards

Andreas

Andreas:
Hello,

update of ADR1399LS8 on PCB#1 ageing 7kHr after putting into Hammond die cast enclosure and with temperature compensation (sensor on bottom of the hammond case)
see also
https://www.eevblog.com/forum/metrology/adr1399-reference/msg5152335/#msg5152335


The ADR1399LS8 have now 10.3 kHrs in total operating time. Tempco is calculated out for the ageing curves.
These LS8-devices are drifting upwards.

The voltage shift at the 2 LM399 (only for comparison) occurred after repair on the output connector. (while operating the cirquit).
The investigation of the PCB did not give a obvious damage.
So I decided to replace the multiplexer for the LM399. This was obviously the reason for the defect as the readings reverted to the old level.
For the future I will drop the defective readings.

with best regards

Andreas

Andreas:
Hello,

update of ADR1399LS8 on PCB#1 ageing 8kHr after putting into Hammond die cast enclosure and with temperature compensation (sensor on bottom of the hammond case)
see also
https://www.eevblog.com/forum/metrology/adr1399-reference/msg5226999/#msg5226999


The ADR1399LS8 have now 11.3 kHrs in total operating time. Tempco is calculated out for the ageing curves.
These LS8-devices are drifting upwards.

I had again a 5-6 ppm voltage shift on the 2 LM399 (only for comparison) on the 2nd Multiplexer (MAX4052A).
This time I had no obvious reason for the shift. So it was very unreasonable that the Multiplexer should have died again.
I reflected what I did last time:
- Switching power off and on (on another desk) to do some measurements.
- Measurements did not show any obvious error.
- Exchange the MAX4052A. (with power off).
- reassembling and putting all back to the measurement desk.

So I decided to do power cycling only and actually this "cured" the 5-6 ppm voltage shift.
Obviously there is some "latchup effect" which affects the upper channels.

But what can the reason for this latchup effect be?
I had introduced some level shifters to reduce the self heating of the multiplexers when having 5V logic levels.
But the level shifters are relatively high ohmic (BSS138 with 330K pull-up resistors on the 15V side) to reduce self heating.
Simulation with a similar FET (BSS123) showed around 20 us rise time with 20 pF for wiring and input capacitances of the multiplexers.
Should this be the reason for the latchup-effects?

with best regards

Andreas

Andreas:
Hello,

update from ADR1399 PCB#2 now at 4 kHrs for the metal can devices (KHZ) and 4.1 kHrs for the LS8 devices (first 100 hours not shown):

See also
https://www.eevblog.com/forum/metrology/adr1399-reference/msg5226966/#msg5226966

The values are all temperature compensated (temperature sensor at the bottom of the hammond die cast housing)
The LS8 devices continue to trend to a slow upwards ageing slope like the TO-46 metal can devices.

If I look closer there are also 0.5-1 ppm jumps on the measurements.
One jump in down direction is on the same day as the power cycling together with PCB#1 (same transformer).

so I started to investigate (see zoomed diagram).
And actually: every time when I did a power cycling (half a minute followed by >15 minutes warm up time) the measurements started at lower levels.
After one measurement cycle mostly the higher level was again active.
So also here I have a less pronounced "latchup effect" of 0.5-1 ppm.

So the question arises: Are there any multiplexers like MAX4052A which can be used as replacement (hoping that there will be no latch up effect)
- low leakage current
- operating from 12-15V (single supply)
- in SO-16 package with same pinout as 4052 devices
- at best with integrated low power level shifters from 5V to 15 V

with best regards

Andreas



with best regards

Andreas

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