Mitsubishi Q172CPU User Manual page 193

6 INSPECTION AND MAINTENANCE
Input Circuit Troubleshooting and Corrective Action (Continued)
Condition
• Sneak path due to the use of two power
supplies.
Input signal
does not
turn OFF.
Depending on short response time setting, noise
False input
is imported as input.
due to
noise
Cause
E E
1 2
E >E
1 2
<Calculation example of Example 4>
For the case with a switch with LED indicator connected to Q172LX,
causing 4 mA leakage current.
Leakage
current 4mA
3.6K
(a) The 0.18 mA OFF current of the Q172LX is not satisfied. Connect a resistor as
shown below.
4mA
I 3.82mA
R=
3.6K
24VDC
(b) Calculate the connecting resistor value R as indicated below.
To satisfy the 0.18 mA OFF current of the Q172LX, the resistor R to be connected
may be the one where 3.82 mA or more will flow.
I I Z(Input impedance): R
R: Z=
I
Z
R Z(Input impedance)=
I
R
R<264 .
Assuming that resistor R is 220 , the power capacity W of resistor R is:
W = (Input voltage)
(c) The power capacity of the resistor selected is 3 to 5 times greater than the actual
current consumption. 220 [ ], 10 to 15 [W] resistor may therefore be connected to
the terminal in question.
• Use only one power supply.
• Connect a sneak path prevention diode.
(Figure below)
Input module
Change response time setting.
Example : 10ms
Q172LX
Motion CPU
module
24VDC
Q172LX
Iz=0.18mA
Input impedance
5.6K
0.18
5.6 10 =264[ ]
3.82
2 2
÷ R = 26.4 ÷ 220 = 3.168 [W]
6 - 26
Corrective action
E E
2
1
20ms
3
Input module