View Full Version : Why RS232 and RS484 ports on VFD's?

02-05-2013, 08:00 AM
I'm shopping on-line for a new VFD for a new-to-me Bridgeport I just bought.

I see that they offer RS232 and RS484 communication ports, among other accessory cards.

What would they typically be used for?

John Stevenson
02-05-2013, 08:04 AM
If you have a range of machines you can bulk program the VFD from a laptop via the port.

02-05-2013, 08:09 AM
I'd imagine that you'd use it for spindle speed control if you were CNCing something.

J Tiers
02-05-2013, 08:19 AM
You can have some external controller set speeds etc based on feedback. We have made such things for clients, to control air flow, etc, and the ability to set parameters on the fly is essential for that. Some VFDs have a small PLC embedded, enhancing those capabilities.

Then also, some VFDs have the ability to be programmed from a form of datastick that can be plugged into the comm port. If you have several dozen VFDs in a system to program, what could take a rather long time to do is much faster and easier with the port.

02-05-2013, 09:39 AM
Like others have said, remote control and setup.

RS-232 is good for about 30 feet or so. RS-485 is good for 4000 feet (differential signaling) and is addressable so you can have multiple devices on the same bus.

02-05-2013, 11:43 AM
macona states it well.

RS485 is the way to go unless you have a propriatary comm system from SqD, Siemans, AB or the like. Mostly more noise resistant with clearer comms signals passing through and higher speed for better performance.

Besides remote programming we have installed them with PLC (programable logic control) systems. This allows for remote monitoring and indivigual control of motors and fault monitoring in an industrial enviroment. Complete plant interface and control. Several brands of VFDs have internal clocks and timers to monitor run time to schedule maintenance for example. Monitor faults for trouble shooting. Monitor motor load for tooling changes, dull tools increase motor load. Many, many other things. This also ties into CNC and touch screen control. Allows connection and control of such devices as pressure/strain sensors and all industrial controls. Photo eyes, color monitoring, level control, temperature, laser reading, bar code read and application. And on and on. The list is almost endless anymore. Pretty limited when I started in the 80's but close to limitless now. Run/monitor your mill from your cell phone a thousand miles away. Great fun.

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02-05-2013, 11:54 AM
Yes to the last prior posts.

At the HSM level they are also used to access things not possible or practicable from the front panel. Example - on the Hitachi WJ200 series vfd (among a few other Hitachi models) there is a little PLC. You can access and program that PLC from the free Hitachi software at great distance via the RS485, or locally via the USB connection. You can't do that from the front panel. I'm about to use this to integrate the oil pressure switch in a SAG12 lathe to mimic the original electromechanical install - no pressure within 20 seconds and the VFD will disconnect the clutches, display a remote alarm and shut down the motor.

02-05-2013, 11:57 AM

02-05-2013, 12:57 PM
Mach and other systems have a Modbus interface plug-in that most VFD's have now for all control, rpm fwd/rev/stop to be done over the link rather than external wiring, pots etc.

02-05-2013, 01:39 PM
Thanks guys.

Those kinds of features are not something I'll likely need to consider for my home application.