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Hioki RM3545 mini teardown

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gamalot:

--- Quote from: PA0PBZ on June 09, 2016, 06:38:31 pm ---
--- Quote from: lukier on June 09, 2016, 06:29:02 pm ---Something is crazy there. There seem to be 37 single channel optoisolators on the digital board alone (probably floating the signals on the big DB connector), and then 25 optoisolators on the analog board - crazy! Why not put MCU/CPLD on the floating side and just transfer some SPI over isolation barrier.

--- End quote ---

Yeah, I was wondering the same, this is just insane. Is that where optocouplers breed?  ;)

--- End quote ---

I was shocked by those optocouples too!  |O

Kleinstein:
The big blocks (T506) and similar seem to be transformers. They should provide isolation from the digital side to the analog side. There are 2 small SOT23 transistors for each transformer - so maybe a kind of royer converter or similar (though I am missing the series inductors for a classical royer). There is no need to have feedback  - there are lots of 78xx (TO220) behind it to do the fine regulation.

The effective number of bits is not that critical. For slower readings averaging can give a higher effective number of bits, even more than 24. The limiting factor is more the INL and maybe gain / offset drift. If the INL is well behaved it might be even possible to use some compensation / corrections.

gamalot:

--- Quote from: gamalot on June 09, 2016, 06:48:59 pm ---
--- Quote from: lukier on June 09, 2016, 06:37:02 pm ---Aaa so these chunky SMD inductors are just filters? (T506 etc) I thought these are some isolated DC-DC converters, but I don't see controller chip and feedback optocoupler.

--- End quote ---

I think maybe it is just a common mode filter.  :)

--- End quote ---

I think I was stupid! They must be DC-DC converters, cuz there is no way to have negative voltage without them!

I need to re-open it tomorrow and see if there is anything on the bottom side of analog board, it's 5 in the morning, I wanna sleep ......  :=\

gamalot:

--- Quote from: Kleinstein on June 09, 2016, 07:07:22 pm ---The big blocks (T506) and similar seem to be transformers. They should provide isolation from the digital side to the analog side. There are 2 small SOT23 transistors for each transformer - so maybe a kind of royer converter or similar (though I am missing the series inductors for a classical royer). There is no need to have feedback  - there are lots of 78xx (TO220) behind it to do the fine regulation.

The effective number of bits is not that critical. For slower readings averaging can give a higher effective number of bits, even more than 24. The limiting factor is more the INL and maybe gain / offset drift. If the INL is well behaved it might be even possible to use some compensation / corrections.

--- End quote ---

YES! I think may be  maybe you are right, the royer convertor has lower noise, it is perfect to be used here, I will try to figure it out tomorrow.  :)

gamalot:

--- Quote from: gamalot on June 09, 2016, 07:18:57 pm ---
--- Quote from: Kleinstein on June 09, 2016, 07:07:22 pm ---The big blocks (T506) and similar seem to be transformers. They should provide isolation from the digital side to the analog side. There are 2 small SOT23 transistors for each transformer - so maybe a kind of royer converter or similar (though I am missing the series inductors for a classical royer). There is no need to have feedback  - there are lots of 78xx (TO220) behind it to do the fine regulation.

The effective number of bits is not that critical. For slower readings averaging can give a higher effective number of bits, even more than 24. The limiting factor is more the INL and maybe gain / offset drift. If the INL is well behaved it might be even possible to use some compensation / corrections.

--- End quote ---

YES! I think may be  maybe you are right, the royer convertor has lower noise, it is perfect to be used here, I will try to figure it out tomorrow.  :)

--- End quote ---

They are all switching power supplies without negative feedback.  ;D

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