Genicom 3600 Electromagnetic and Radio Frequency Interference, Ground Loops Between Equipment

3600 Printer Maintenance Manual

Electromagnetic and Radio Frequency Interference

Noise induced in interface cables can result in the printer receiving false data. This condition may cause the printer to skip printing a label or lockup. Sources of electromagnetic interference (EMI) and radio frequency interference (RFI) are radio transmitters, ignition systems, and relays. To eliminate the effects of EMI and RFI, use low capacitance, twisted pair, shielded cables. Route cables away from sources of EMI and RFI such as large inductive motors or fluorescent lighting ballasts. Do not run cables near AC power lines. If communication cables must run near AC power lines, cross them at 90 degree angles. Eliminate ground loops; they act as receiving antennas for RFI. Limit the number of breaks (connectors) in the cable. It is possible to use a power line monitor, such as the BMI 4800, to test for noise on the interface cable.

Ground Loops Between Equipment

Ground loops pick up RFI as well as generate their own noise in interface cables. The recommended wiring of the interface cable calls for connecting chassis ground (pin 1) between the host computer and the printer to ensure that the chassis of both devices remains at the same electrical potential in the event of a faulty ground in either device. This safety precaution will save people from electric shock in the situation where they touch both the host computer and the printer at the same time while there is a faulty ground in either device. With this wiring, you would normally expect problems with ground loops, but the printer, chassis ground, and signal ground are connected to each other through a 10kΩ resistor, thus providing some ground loop immunity.

If connections in the interface cable described above are discovered to cause ground loop problems, disconnect the shield from the backshell at only the printer, and sever the chassis ground (pin 1) connection between the host computer and the printer. To ensure safety, double your efforts to guarantee that both the host computer and the printer make a solid electrical and physical connection to earth ground.

Inadequate Earth Ground

Poor grounds can cause fuses on equipment to blow and damage components. The ground in the AC power receptacle must be a good, solid earth ground. Do not rely on conduit for ground. The ground rod should penetrate the earth at least 8 feet below the frost line. The soil should contain clay minerals; dry, sandy soil does not provide a good ground. Ensure that all ground connections from the service panel to the AC receptacle are solid and secure.

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