Installation
operator and device.
The control equipment may cause the misoperation of the equipment it controls, which
may lead to death or serious personal injury and equipment damage. Therefore, the
TrustPLC CTH200 system must have the emergency stop function, electromechanical
interlock or other redundant safety facilities independent of the CTH200 system.
3.5 Suppression Circuit
Inductive loads should be implemented with suppression circuits to limit voltage rise when the
control output turns off. Suppression circuits protect your outputs from premature failure due to
high inductive switching currents. In addition, suppression circuits limit the electrical noise
generated during switching inductive loads.
The effectiveness of a given suppression circuit depends on the application, and you
must verify it for your particular use. Ensure that all components used in your
suppression circuit are rated for use in the application.
DC Outputs and Relay Outputs which Control DC Loads
The DC outputs have internal protection that is adequate for most applications. Since the relays
can be used for either a DC or an AC load, internal protection is not provided.
Figure 3-4 shows a sample suppression circuit for a DC load. In most applications, the addition of
a diode (A) across the inductive load is suitable, but if your application requires faster turn-off
times, then the addition of a Zener diode (B) is recommended. Make sure the Zener diode can
provide enough current for output circuit.
Figure 3-4 Suppression Circuit for DC Load
AC Outputs and Relay Outputs for AC load
The AC outputs have internal protection that is adequate for most applications. Since the relays
can be used for either DC or AC load, internal protection is not provided.
Figure 3-5 shows an instance for the suppression circuit of AC load. In most applications, the
additional MOV resistor can be used for limit the peak voltage and protect the internal circuit in
CTH200 PLC. Make sure the operation voltage for MOV is at least 20% greater than regular line
voltage.
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