Toshiba PROSEC T1 T1S, 6F3B0250 user manual Led

6F3B0250

3. I/O Application Precautions

(5)Countermeasures against leakage current

When a switch with an LED or an AC output sensor is used, the input sometimes cannot recognize that the switch is off due to the current leakage. In this case, install a bleeder resistor to reduce input impedance.

LED Bleeder resistor Bleeder resistor

R	T1
	input
C	circuit
V

DC input type

AC	R	T1
output		input
sensor	C	circuit
	V
	AC input type

Select a bleeder resistor according to the following criteria:

(a)The voltage between the input terminals must be lower than the OFF voltage when the sensor is switched off.

(b)The current must be within the allowable range when the sensor is switched on.

(c)Calculate the wattage of the bleeder resistor by multiplying the current when the sensor is switched on times three.

Note) The above solution cannot be applied to the T1-16 dry contact input.

(6)Countermeasures against induced current

With ac input signals, if the external cable is long or if a multi-core cable is used, an induced current can flow from the charged wire to the open wire, in proportion to the capacities of the cables. In this case, sometimes the voltage reaches the level of the ON input even though the contact is open, causing the input to malfunction for no apparent reason.

The usual practice when this happens is to reduce input impedance. Install a resistor or a resistor and capacitor between the input and common terminals, or use shielded cables. Such precautions are necessary when dealing with a large number of ac input signals.

~

C

V

Open contact

T1 input circuit

64 T1/T1S User’s Manual

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