ADLINK cPCI-7252 - Manual (Page 38)

28 Operation Theory
The LPCI-7250 contains 8 identical opto-isolated control input
channels through PC3H4 photo-coupler. The circuit is shown as
the following diagram:
Figure 4-5: LPCI-7250 Differential Input Circuit
In addition, a single-pole filter with a time constant of about 5ms is
used to filter AC inputs passing through.
The normal input voltage range for an active high state is 3 to
24VAC or DC. The normal input range can be extended by chang-
ing the resister (Ri) to limit the current (IF) through the PC-814
(opto-isolator to about 10mA). The exact resister value to replace
the original resister Ri (1.2K
Ω
) can be calculated by the following
formula.
Vin = IF x Ri
Pw = Vin x IF
For example, if the input voltage is 110V, then the Ri should be
replace by
Ri = 110 (V) / 0.01 (A) = 11 K
Ω
Pw = 110 (V) X 0.01 (A) = 1.1 W