IDEC MicroSmart Pentra - Manual (Page 42)

3: I NSTALLATION AND W IRING
3-14 W EB S ERVER CPU M ODULE U SER ’ S M ANUAL FC9Y-B1278
Precautions for Connecting Communication Devices
When connecting communication devices to the Web server CPU module, take possible external noise sources into
consideration.
In a communication network consisting of a Web server CPU module and an external device (a communication device
which has a functional ground and a signal ground connected together internally [for example, IDEC’s HG3F and HG4F
operator interfaces]), if all devices are powered by a common AC or DC power source, noise generated by the external
device may affect the internal circuits of the Web server CPU module and the communication device. Take the following
measures depending on the operating environment.
• Use a separate power supply for the external device generating noises so that a loop circuit to induce noises can not be formed.
• Disconnect the functional ground terminal of the communication device from the ground line. This measure may result in
deterioration of EMC characteristics. When taking this measure, make sure that the EMC characteristics of the entire system are
satisfactory.
• Connect the functional ground terminal of the communication device to the 0V line of the power supply so that the noises from
the external device do not flow through the communication line.
• Connect an isolator to the communication line so that a loop circuit to induce noises can not be formed.