Pulse Waveform Shaping Method - Mitsubishi Electric RD62P2E Application User's Manual

Pulse waveform shaping method

To shape pulse waveform effectively, increase the load current in cables by inserting a dummy resister of several hundreds 
(/several W) between the pulse input terminals connected to a pulse generator. The greater the load current, the more
effective this method is.
The following figure shows an example of the connection of a dummy resistor at signal level 24VDC:
• Connecting a dummy resister at 24VDC
RD62P2, RD62P2E
6.8kΩ
1/3W
Phase
A
ABCOM
6.8kΩ
1/3W
Phase
B
Shaping a pulse waveform is effective as a countermeasure against the following two cases.
Distance between the pulse generator and the high-speed counter module is long.
The waveform distortion is corrected and the pulse waveform becomes stable.
Waveform is distorted under a noise environment.
The pulse waveform becomes stable by shaping the waveform, which has an effect on external noise reduction.
The following example describes how to evaluate the resistance constant and rated-power of a dummy
resister. For example, if a load current of approximately 30mA is set, the resistance constant of a dummy
resistor is given by:
R = V  I = 24V  30mA = 800
and the voltage applied to a dummy resistor is given by:
P = V  I = 24V  30mA = 0.72W
Select a dummy resistor with the rated power of 2W, considering the design margin.
Shielded twisted pair cable
24V
A20(A13)
B19(B12)
Shielded twisted pair cable
24V
A18(A11)
Apply a dummy resistance of several hundred ohms
(/several watts) across the pulse input terminals
(between 24V and ABCOM).
Shield
Shield
3 TROUBLESHOOTING
3.3 Troubleshooting by Symptom
3
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