Mitsubishi Electronics manual 154

11TROUBLESHOOTING

11.5 I/O Module Troubleshooting

MELSEC-Q

This chapter explains possible problems with I/O circuits and their corrective actions.

11.5.1 Input circuit troubleshooting

Example 1

Example 2

Example 3

Example 4

This section describes possible problems with input circuits and their corrective actions.

Input Circuit Problems and Corrective Actions

Condition			Cause					Corrective Action
	• Leakage current of input switch						• Connect an appropriate resistor which will
	(e.g. drive by non-contact switch).						make the voltage across the terminals of the
						AC input	input module lower than the OFF voltage
Input signal							value.		AC input
			Leakage			Input module
does not			current
turn OFF.									Input module
			Power supply
							It is recommended to use 0.1 to 47 F + 47 to
							120 (1/2W) for the CR constant.
	• Drive by a limit switch with neon lamp.						• Same as Example 1.
					AC input		• Or make up another independent display
Input signal							circuit.
does not		Leakage			Input module
turn OFF.		current
		Power supply					• Same as Example 1.
	• Leakage current due to line capacity of wiring
	cable.						• However, leakage current is not generated
	(Line capacity C of twisted pair wire is approx.						when the power supply is located in the input
Input signal	100 pF/m).						equipment side as shown below.
					AC input					AC input
does not
turn OFF.			Leakage		Input module					Input module
			current
		Power supply						Power supply
	• Drive by switch with LED indicator.						• Connect a register which will make the voltage
				DC input			between the input module terminal and
				(plus common)			common lower than the OFF voltage, as
							shown below.
		Leakage								DC input
		current			Input module					(plus common)
Input signal
does not								Resistor
turn OFF.										Input module
							A calculation example of a value for a
							connected resistor is given on the following
							page.

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