PCI-P16R16 Series User Manual (Ver.2.8, Apr. 2011, PMH-013-28)
24
Although the normal input voltage range is 5 to 24 V
AC
or V
DC
, the input can still be
changed to a larger range by choosing suitable external resistors. The following
figure shows how to connect to a larger input. Please note that the input current
should be limited between 2 mA to 20 mA; too large an input current will burn
down the internal resistor Ri, while too low of an input current will not active the
photo-coupler isolator. Calculate input voltage and current, then replace resister
Ri.
PC - 814
R
i
= 1.2 k
Ω
/1 W
I
f 20mA
Vin
On board circuits
External Circuit
Figure 2-4. Isolated Digital Input
I
f =
2 mA ~ 20 mA
A rough estimate:
if Vin = 120 V and we ignore photo-coupler turn-on voltage.
We’ll get:
Vin /
I
f =
Ri
Vin = 120(V) ,
I
f
=10(mA) , Ri = Vin/
I
f
120(V) / 0.01 (A) = 12000 (
Ω
)
If you replace
12
k
Ω
as resistor Ri, we can calculate the power consumption of Ri
as follows:
P = I
2
R
ex
= (10 mA)
2
* 12 K
Ω
= 1.2 W
The power consumption is 1.2 watts, but choosing 1.5 or 2 watts is better.
Thus, we can choose a 12 K/2 W resistor to replace the resistor Ri.