Toshiba V Series User Manual page 143

Also, when the bleeder resistor is selected in the above manner, the contact current
at the switch ON state should be checked.
(5) If the two-wire proximity switch and other solid-state switches are used, be sure that
there is no possibility of mis-inputting because of the leakage current, as in
procedure (4). (See (4) for details on how to select a bleeder resistor.)
Also in this case, because of the effect of the saturation voltage (voltage drop) at
ON, regardless of whether the switch is ON, the input terminal voltage may not be
able to reach the ON voltage, thereby falling to read as input ON.
If input voltage is low or if wiring is too long, special measures are necessary.
If the cable resistance value is expresses as R[ Ω ], Vd[V] for the voltage drop of the
proximity switch, and Zi[ Ω ] for the input impedance of the input modules, the voltage
Vi[V] applied between the input module terminals will be as expressed below (when
the proximity switch is ON) :
I f the above Vi is lower than the minimum ON voltage of the input module, input
voltage V must be raised or the value of the cable resistor R must be made smaller.
(6) Because the input filter time constant of the high-speed response input module
(DI635H) is set to small, the input module may read the wrong input due to chattering
of the contact. Use the high-speed response input module to connect with solid-state
devices. Also, take measures to suppress noise.
(7) If input wiring is too long, take measures to prevent erroneous input caused by
noise, as follows.
•
•
•
•
•
6F8C0836
Contact current
= 24[V]
Two-wire proximity switch
Sensor
V-Vd
Vi = Zi
2R + Zi
Wiring length must be minimized. Do not make unnecessary loops.
Keep the input wires away, at least 200mm, from power cables and high
frequency lines, or shielded the input cables with a metal plate.
If possible, use relays at the leading in the control panel.
For some cases, use a shielded cable or twisted-pair cable.
Install a bleeder resistor to reduce input impedance.
3.1 Precautions for DC Input Modules
Ω +
3.0[k ] R
× =
16 [mA]
Ω ×
3.0[k ] R
Cable resistance (R)
Cable resistance (R)
COM
V
Input module
121
3