wincros@xxxxxxxxxxxxx writes:
<< That is interesting information, especially to see the improvements
in design over time. Are you also saying that Olympus did bad
engineering on the OM4T circuits when they designed it?
>>
Hi Winsor,
Design is always a compromise between conflicting
requirements,engineering culture and part availability. The OM4 was actually
designed a while ago when EEPROM pots were not available. Small serial EEPROM
memory chips typically used for storing cal constants do date back to at
least early '80s but were not available in 3V versions early on.
Field calibration without special equipment by small repair shops may have
been an important design requirement leading to putting in pots.
Others mentioned on the list that CE mark versions of the OM3 use internal
calibrations stored in memory but with no field programmable mode. To do this
better they could have put in a way of reprogramming the constants in a
field service mode but they may have had memory constraints in the low
voltage microcontroller they used. The OM4T does include a test program mode
for field service setup of voltage levels, pots etc.
Sometimes it is not possible to get away without some sort of potentiometer
even where internal uP calibration is used. Usually you give up a bit of
potential dynamic range to allow for component or sensor tolerance when doing
internal self cal. Pots allow you to adjust for tolerance buildup to maximise
dynamic range. In the case of the OM4 there is so little space inside that
they use a single "jungle" analog chip for the analog functions this tends to
compromise the performance of each of the blocks. With only 3V, avaialble
dynamic range is likely to be much more of a problem. While there are now
many more analog chips which run off 3V or less at the time the OM and OM2S
were designed low power, low voltage chips were rare and of lower
performance. This probably made it much more difficult to do an adjustment
free design.
Regards,
Tim Hughes
>>Hi100@xxxxxxx<<
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