Toshiba SX 2000 - Manual (Page 129)

Chapt.3 Precautions for I/O Modules
(3) The examples of connection with transistor output devices such as proximity
switches are shown as follows.
• NPN open collector type (+common)
(4) If a switch with an LED display is used, the current (leakage current) through
the LED may cause the erroneous input (always ON). In this case, install a
bleeder resistor to lower the input impedance.
LED
(An example of selecting a bleeder resistor R)
When the voltage between input terminals is Vd at the switch OFF state
(with no bleeder resistor), the resistance (R) and the wattage (P) of bleeder
resistor can be selected as follows.
In the case of DI633,
V=24Vdc, Input impedance Zi=3.0KQ, OFF voltage Vo=3.6Vdc
Leakage current IL=2mA,
3.0R[KO]= 3.6[V]
-x2 mA < •
3.0[KQ1 + R R
As a result,
R < 4.5[KQ1 ^ R = 3[KQ1
P =
(24[Vlf
3ooora
x(2.5-3)=0.5rwi
Also, when the bleeder resistor is selected in the above manner, the
contact current at the switch ON state should be checked.
Contact current= 24 [V]x|^^t!i?L±B = i6[mA]
3.0[K p ^ R
1 1 2 Sequence Controller S2T