Mitsubishi Electric MELSEC iQ-R Series User Manual page 53

Pulse shaping method
As one action against external noise and waveform distortion, this section describes a pulse waveform shaping method using
a dummy resistor.
To shape a pulse waveform, it is effective to increase the load current within the cable by inserting a dummy resistor of
approximately a few hundred ohms (/a few watts) between the pulse input terminals connected to the pulse generator. The
larger the load current, the more effective this shaping method is.
The following countermeasure results can be obtained with this shaping method.
• Improved waveform distortion and stabilized pulse waveforms when the wiring distance between the pulse generator and
the pulse input module is large
• Stabilized pulse waveforms and suppressed influence of noise by way of waveform shaping when the pulse waveforms are
disturbed in environments where external noise is present
Ex.
The following shows a connection example of a CH1 dummy resistor with a signal level of 24VDC.
Pulse input module
360Ω
1/3W
100Ω
15kΩ
1/10W
1/10W
An example showing how to select the dummy resistor (how to calculate the resistance contact and rated power of the dummy
resistor) is given below.
Target
Resistance constant of the dummy resistor (load current: approximately
30mA)
Rated power of the dummy resistor (load current: approximately 30mA)
From the calculation results in the above table, it can be seen that it is beneficial to add a dummy resistor of 800 (/2W)
between the pulse input terminals.
Install a dummy resistor of approx. several hundred Ω
(/several W) between the pulse input terminals
(CH
CH1 V+
1.8kΩ
1W
CH1 V-
FG
V+ - CH V-).
Shielded twisted pair cable
Shield
Calculation method
Calculate the resistance constant (R).
• R = V  I = 24V  30mA = 800
Calculate the power (P1).
• P1 = V  I = 24V  30mA = 0.72W
From the power (P1), calculate the power including the margin (P2).
• P2 = P1  2 = 0.72  2 = 1.44W (approximately 2W)
3.3 Troubleshooting by Symptom
3 TROUBLESHOOTING
3
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