Toshiba SX 2000 - Manual (Page 130)

(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.
3.1 Precautions for DC Input Modules
If the cable resistance value is expresses as R[Q], Vd[V] for the voltage
drop of the proximity switch, and Zi[Q] 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):
... V^Vb
V i =---------------- Zi
2R + Zi
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 constant. 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.
• 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.
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