Rainbow Electronics LM81 - Manual (Page 17)

Functional Description
(Continued)
Counts are based on 2 pulses per revolution tachometer outputs.
RPM Time per Revolution Counts for “Divide by 2” Comments
(Default) in Decimal
4400 13.64 ms 153 counts Typical RPM
3080 19.48 ms 219 counts 70% RPM
2640 22.73 ms 255 counts 60% RPM
(maximum counts)
Mode Select
Nominal
RPM
Time per Revolution
Counts for the 70%
RPM
Time per Revolution
Given Speed in Decimal for 70% RPM
Divide by 1 8800 6.82 ms 153 6160 9.74 ms
Divide by 2 4400 13.64 ms 153 3080 19.48 ms
Divide by 4 2200 27.27 ms 153 1540 38.96 ms
Divide by 8 1100 54.54 ms 153 770 77.92 ms
DS100072-12
(a) Fan with Tach Pull-Up to +5V
DS100072-13
(b) Fan with Tach Pull-Up to +12V, or Totem-Pole
Output and Resistor Attenuator
DS100072-14
(c) Fan with Tach Pull-Up to +12V and Diode Clamp
DS100072-15
(d) Fan with Strong Tach Pull-Up or Totem Pole Output
and Diode Clamp
FIGURE 7. Alternatives for Fan Inputs
LM81
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