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using STM32H750XB ADC to read 4-20mA transmitter signal

ksale.1
Senior

Hi,

How to connect to the preamp in order to use smaller R and reduce the voltage drop, the reference manual table below is not clear to me, particularly the internal column, please see figures below.

0693W00000WIbtlQAD.jpg0693W00000WIbtvQAD.jpg

2 REPLIES 2
AScha.3
Chief

why you need use extra preamp?

with R 150 ohm you get perfect input range and have max. 3 V drop .

just add some input protection.

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ksale.1
Senior

Hello @AScha.3​ 

"The sensor transmitter needs a certain voltage. You have a line. You have a drop over the lines, over the wires, so you would like to maintain as much voltage as possible for the loop and not wasting, let's put it this way, erasing voltages inside the module. 

So for example, if you take the gain of 4, we can reduce the resistor from 150 ohm down to 38 ohm. This actually leads to a voltage drop of about 800 millivolt, which is four times less compared to the 3.3 volt with the 150 ohm"