I work on escalators that use ethernet cables to send signals from "nodes" to a PLC. the only tool available is a Fluke multimeter. is there a way of reading these signal using the meter? or do I need different tools/meters? is the signal a voltage signal or a hertz signal or some other signal?
Ethernet is a "hertz" signal. You can not test it with a multimeter.
However, just because you are using an ethernet cable doesn't mean that ethernet signaling is being used. Simple signaling can be done over ethernet cabling, such as rs-485 or simple Form C signaling (such as used in relays, i.e. thermostats). Are you sure that it using ethernet signaling?
There's two types of ethernet cable testers:
1) Continuity testers, which only test that there is a straight-through electrical connection from one end of the cable to the other. These can be had for cheap, like $25 to $250 or so. all they test is conductivity and that the cable is wired properly. more expensive testers can detect more types of mis-wires.
2) Cable certifier, which in addition to doing most (if not all) of what a continuity test can do also certify that the cable meets certain specification, such as CAT5 or CAT6, etc.
If it's just form c signaling, you can use a multimeter.
You need different tools. The best you can hope for with a basic multimeter is basic continuity, which is better than nothing..but not by much. There are relatively cheap units that can confirm appropriate pin-outs, isolation, etc and there are higher dollar TDR-type units (Fluke makes some good stuff, but not cheap) that can actually certify the actual performance levels of the cable or - in the event of a fault - where along the cable the issue has occurred.
There are different levels of network cable testing
Cable certification testers guarantees cabling system compliance to industry standards.
Cable qualification testers determines if an existing cabling link can support certain network speeds and technologies.