What does the star under the resistors R16, R17 and R18 indicate?
The CD4047's are one-shots triggered by optical sensors using LED's (Light emitters are bi-directional as PD's). They each use large caps so a slow pulsing sound is chosen by R to drive the buzzer at unique rates to detect HIGH OK and LOW.
So make LEVEL OK R= 1M or such that the buzzer stays on steady or the duration between pulses,
Then make HI and LO different from each other with smaller R's .