RS232 longest distance

What is the longest distance you can run an RS232 cable from a PLC to a field device?

I have an application where the distance is about 100ft. I have read that it is a good idea to keep the length under 50ft.

RS232 spec will say 50 ft. I have gone as much as 175 feet without problems. Shielded wiring ,dicated conduit.

100 feet is no problem, even though outside the spec. Just be sure to use a very low capacitance cable, with a good shield.

When you get problems go down with the baudrate.

The maximum distance you can go with an RS232 cable is 2500 pF.

Extending RS-232 beyond 50 feet

The RS-232 spec simply suggests that a maximum distance of 50 feet is more or less "guaranteed", though I've had numerous customers exceed this. Factors that can diminish your performance across longer distances can include, but are not limited to heavy RF "noisy" environments, and even fluorescent lighting. If you're looking to extend beyond 50 feet, ******* makes a DeviceMaster RTS product which offers RS-232 to Ethernet connectivity, so that your RS-232 serial cable run can be within the 50 feet limitation, and then standard CAT 5 Ethernet cable for the longer runs... For simplicity sake, you could even put a second DeviceMaster RTS on the other end of this run and simply "tunnel" between these two units. Please feel free to contact me for further details.

Jason Reiling
*******
763-494-4144

As others have said:

Capacitance: Lower is better. Look for EDDC = Extended Distance Data Cable.

Voltage of the devices: Using devices that have a +15v to -15v signal switch requires more drive than -3v to +5v.

Baud Rate: Most of the times lower baud = longer length = better signal.


Consider using a current loop for high noise, long length runs. Black Box (Blackbox.com) has my prefered brands that I've used up to about a mile and take RS-232 at each end. Some can be powered by the CTS/DSR signals present on the serial devices.

Also consider RS-422 converters at each end, but most people try to use them with 2 wires and should have used 4 wires. Better brand Current loop converters can do full duplex over 2 wires.

If you can afford them, get yourself some RS-232 to Fiber Optics converteres...and some fiber. There are a lot of good ones in the market, like B&B Electronics, they can convert almost anything.

Somehow, the benefit is high and the relative price is low.

Thanks for all the help!
I am going to use the Belden blue hose for the RS232 cable since I am only using pins 2,3,and 5. I think that this will be a good shielded cable for the application.