hi mr. AL,
i had tried this but there is loss of linearity through optoisolator which is creating the problem.
Hi again,
No no, you only loose linearity when you use the 'standard' run of the mill opto as a linear device. The system i proposed uses the opto as a digital element, which does not loose linearity.
The AD converter in the slave uC chip converts the analog signal to be measured into a digital word (or words), and that is what is transmitted through the opto isolator, not the analog signal.
For example, if we have a power supply of 5.12 volts and we measure an analog signal of 10mv we would get a digital word of:
00000010
That is then transmitted through the opto isolator and comes out the other (isolated) side as:
11111101
and we simply invert that and get back the original digital code:
00000010
and that is what ultimately gets transmitted to the host, which probably stores that sample.
Note in the above i had shown 8 bits out of 10, the first two are both zeros.
Here's a rough block diagram:
Signal o--->ADC--->DIGITAL--->TRANSMIT--->OPTO--->MASTER_RECEIVER
Note that in the above the OPTO is in the digital signal path, not the analog path. Doing it this way maintains linearity as well as accuracy. The cost for 10 bit accuracy is about 1 dollar US per channel, plus the cost of the opto's and the 5 masters and 1 super master.
A system which does not work looks like this:
Signal o--->OPTO--->RECEIVER
where the OPTO is a common garden variety, and that is *not* the system i proposed.