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A more narrow lesson: this is why all SQL statements involving NULL are always false.

> in any case, losing power means the transmitter stops transmitting.

> and here's the fun part: your circuit which controls that inserter is set to insert "if [ICE] < 8000"

> and GETTING NO SIGNAL AT ALL counts the same to it as ICE=0.

> 0 is < 8000.




In industrial automation, one old and popular analog signal scheme is the 4–20 mA current loop [1]. Why 4mA instead of 0mA? Because that way, you know 0mA specifically indicates a fault caused by a failed sensor, break in the line, etc.

[1] https://en.wikipedia.org/wiki/Current_loop


A CHECK constraint treats NULL as true.




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