problems with ethernet cable

[italo2008 0]

Hi (and sorry for my English I need to connect an operator panel (producted by Siemens) with VIPA plc, using an ethernet cable. I tried with a 10 meters long straight-thru cable and it works correctly, but using a longer cable (15 or 20 meters) there's no communication. I checked cable ends and i verified that there's current in the cable and everything is OK 1) the lenght of the cable may be a problem? 2) I know that a stright-thru cable must have the same order in the two cable ends, but can I decide this order or there's a specific order that I must follow?) thanks

[aggattapauer 2]

ethernet arriva al massimo a 100 mt. Quindi nel tuo caso sei abbondantemente nei limiti. Il cablaggio è molto importante e sì devi seguire un cablaggio preciso poichè il cavo è composto da 4 coppie di fili intrecciati tra loro il che elimine determinati disturbi elettromagnetici generati dal cavo stesso. Cerca su internet la sequenza di colori giusti da crimpare.

[paulengr 44]

I hope you aren't detecting any current at all. Ethernet uses voltage signals for communication and very low level (1.5-2.5 volts maximum). It has isolation transformers at each end, too. Up to 1 Gbps, a properly made CAT 5E cable is good for up to 100 meters (as per the standard). CAT 3 cables are very finicky and often won't work. Normally all end devices use the opposite polarity from all switches. The standard arrangement is to plug each device into a switch. A "straight through" cable is used between the switch and the device because the pinouts are reversed on the switch relative to an end device. If you attempt to connect two end-devices together, or two switches together, the standard calls for a "crossover" cable which has pairs swapped. However, many devices, including most switches, these days support automatic MDI/MDI-X (Media Device Interface) negotiation. This solves the problem of a need for a crossover cable since they can electronically operate in either switch or device mode. It sounds to me like you got lucky with a 10 meter cable. Get the proper cable (a crossover cable) or buy a crimper and make one yourself. If you do make cables, realize that CAT 5E is designed to operate with a 100 MHz bandwidth. This huge bandwidth makes it very, very critical to terminate the cable properly and treat it properly (no kinks, knots, or squeezing it in doors) or you will have problems.