Greetings RS232 Gurus, I have a couple machine tools that connect to a computer through RS232. I now need to run a longer cable for one of the machines. Looking online it seems like the biggest limiting factor is the capacitance of the cable. I have a reel of cable with three twisted pairs and no shield that's about 300 feet long. Measuring the capacitance with my multimeter I find the capacitance is less than
2300pf. This is fine as near as I can tell because I only need to run about 60 feet and the baud rate I need is 19600. I don't know how accurate the meter is except for what the documentation says and it seems like the measurement is accurate enough. So I think the baud rate I want to use will be OK. But I have two questions. First, I measured the capacitance of each pair of wires by stripping the ends and connecting the meter to these ends without touching with my fingers. Each pair was pretty close to the same measurement. Is this the proper way to test the capacitance of the cable? Second, there is no shield in the cable. Since I only need one pair of the three pairs in the cable can I just use the four remaining wires connected together at one end as a shield since all the wires are twisted together? Or should I just go out and buy a cable with a shield and put this reel back into storage with all my other wire? Thanks, Eric- posted
11 years ago