Mitsubishi Melsec-Q Series User Manual page 476

Condition
• Sneak path due to the use of two power supplies.
Input signal is
not turned off.
Stepwise distortion as shown below appears to the
zero cross voltage of input signal (AC).
Input signal is
not turned on
(AC input
Zero cross
module)
voltage
False input due Depending on response time setting, noise is imported
to noise as input.
<Calculation example of the resistance to be connected in Example 4>
• Connecting a switch with LED display, in which a maximum 2.33mA leakage current flows when 24VDC is
supplied to the QX40.
• In this case, the circuit does not satisfy the condition that the off current of the QX40 is 1.7mA or less.
Connect a resistance as follows.
12 - 181
Cause
DC input
E1
E2
E1 E2
Leakage current
2.33mA
I =0.63mA
R
24VDC
• Use only one power supply.
• Connect a sneak path prevention diode. (Figure
below)
Input
module
E1
Improve input signal waveform by using the on-
line system etc.
Change the response time setting.
Example: 1ms to 5ms
(When excessive noise is cyclic, shorter response time
setting may produce a higher effect.) When the above
action is not effective, take measures against noise to
block excessive noise, e.g. avoid tying the power
cables and control cables in a bundle, and add surge
absorbers to the noise sources such as the relays and
contactors used with the same power supply.
QX40
Input
2.33mA module
24VDC
QX40
I =1.7mA
Z
Input impedance
R
5.6k
Corrective Action
DC input
Input
E2
module
(To the next page)