Toshiba T2N User Manual download pdf (Page 67)

3.Application Precautions for I/O Modules

52 PROSEC T2N

(5) When applying an AC input signal, if the external cables are long or if the

number of cores of a multi-core cable is large, a current induced from the

charged wires will flow in the open wire, depending on the mutual

capacitance between the cables. Sometimes a voltage may be

generated which reaches the ON level despite the contacts being open.

In this case, the general method is to decrease the input impedance and

lower the input ON level due to the induced current. Install a resistor or a

resistor + capacitor between input and common, or use a multi-core

shielded cable with a small cable capacitance.

Contacts open Current induced from charged wires flow through

cable capacitance

Current induced from charged wires flows through cable capacitance

For the maximum distance of external cable to an AC input module, it is

necessary either to take the above countermeasure within 100m length in

the condition that, out of 20 cores, 19 are charged wires and 1 is an open

wire, or to check whether the input voltage in this condition is less than the

OFF voltage. When handling large numbers of AC input signals,

precautions such as the above are required. Therefore, taking account of

cost of the system as a whole, one method is to study the interface by DC

signals.

(6) When connecting AC output type sensors, sometimes it is not possible to

detect the OFF state due to the leak current when the sensor is OFF.

In this case, counter by installing an external bleeder resistor as shown in

the drawing below.

AC output type

sensor

Input

module

Bleeder resistor

Select bleeder resistors using the following points as a guide.

1) When the sensor is OFF, the voltage between the input

terminals must be less than the residual voltage in the OFF state

2) The current when the sensor is ON within the allowable value for

the sensor

3) Determine the wattage of the bleeder resistor by making an

allowance of approximately 3 times the current when the sensor is ON.

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Toshiba T2N User Manual Page 67