Hello - I am trying to make a cirsuit that will send a signal to a switch when ph increases above a given value in the 7.6ph. With the attached circuit the millvolts from the ph probe / circuit should be about 33 millivolts. I know I will get drift overtime so I need to make sure I can vary my comparison. I was thinking of using an lm317 chip and knocking its voltage down with a reisitor to get my comparison voltage. Also, I really don't care about the exact ph reading because I am just trying to turn on an acid dosing pump. I can measure the ph seperately and then adjust the comparison to dose at a different point to maintain a wanted ph.
So, my questions are as follows:
Should i use an lm317, can i just compare to ground and knock down the ph millivollts with a pot? Can a pot adjust in such a small range?
What can is use something like a CA3140 MOSFET? is it sensistve enough?
The following are the circuits I have been referencing:
http://www.66pacific.com/ph/simplest_ph.aspx
http://forum.allaboutcircuits.com/newthread.php?do=newthread&f=6
Please give me your thoughts.
THank you,
Anthony
So, my questions are as follows:
Should i use an lm317, can i just compare to ground and knock down the ph millivollts with a pot? Can a pot adjust in such a small range?
What can is use something like a CA3140 MOSFET? is it sensistve enough?
The following are the circuits I have been referencing:
http://www.66pacific.com/ph/simplest_ph.aspx
http://forum.allaboutcircuits.com/newthread.php?do=newthread&f=6
Please give me your thoughts.
THank you,
Anthony