This is general issue pertaining to instruments that we build using the 8052 MCUs.

There are two kinds on a macro level :

CASE_1 :

* Instruments where an ADC or DAC function is involved. These instruments, since they involve an analog part are subject to issues like offset, drift etc. Normally we specify a calibration once in 6 months and generally there have been issues.

CASE_2 :

* Instruments which are purely digital with no analog circuitry - like a simple RPM meter. All it does is to digitally count the pulses and display it. In other words it can be thought of as a simple scaling unit. Does one need to calibrate this instrument also at the same frequency as the instrument with ADC/DAC function ?

I do understand that the MCU clock can drift - but when I am measuring a rpm of 5 to 200, and using a 12MHz crystal with a 6 clocker, the error in output due to the "drift" in crystal frequency will be negligible ?

So, is it OK if I say that in CASE_2, there is no periodic calibration required ? Are there any guidelines to this ?

Thanks

Raghu