Connect a freq. inverter to a FX3GE over a long distance

[Theo V]

Hi everybody, I need to make a set up to start/stop and control the speed of a frequency inverter (Danfoss VLT Aqua) using a FX3GE PLC on an I/O base. The speed I'd like to control by using an analogue signal however, the inverter is aprox. 350 meters away from my PLC controlpanel in a second engineroom in the factory. Will this distance be a problem? Is there a smart solution to make the connection over such a long distance or is it possible with the standard analogue output from the FX3GE? I can use either a 0-10Vdc or a 4-20mA signal to the inverter. From the existing situation some shielded cables are available for the hardwired connections but the PLC function to regulate the motorspeed was built inside the frequency inverter and the other motors are located in an other engineroom and did just start/stop with digital signals without a PLC. I'm using GX-Works2 V1.98 Has anyone experience with a similiar situation? Best regards, Theo V

[kaare_t]

I have not calculated it, but 350m sound a lot for a low voltage signal. Remember that the voltage is reduced xmV for every meter of cable. I doubt that 0-10V will do it, maybe - just maybe - 4-20mA will do it (since 4-20mA will MAYBE tolerate a voltage drop of that much). You will have to calculate how much voltage drop it will be (I think a normal electrician can calcuate this for you based on standard values for the specified cable). However, the standard way of doing this is communication in some form. Use a remote IO station with e.g. ModbusRTU and RS485 to connect to the FX3G (you will need to purchase some additional equipment for the PLC, and check if the inverter is ready for this). What of the above possible for you?

[Inntele]

I agree with Kaare_T. There is a single kind to organize the control by simple I/O: 4-20mA analog loop and discrete inputs on both sides with the 1,6k load resistors in parallel to each input, that allow increase the current on input lines up to 20mA. However don't forget, the analog inputs outputs in FX3 is not isolated with the base unit, and don't forget about other strong factors like lightning and welding works that may destroy your PLC. So a correct step is to use RS485 communication for these purposes. So to solve your task I'd take 2 modules FX3U-485ADP-MB, one FX3S base module, necessary accessories to connect communication modules to the base units. Then I'd organize N:N network between PLCs. It will be a simplest, cheapest and high-speed solution to make data exchange the FX3GE with VFD.

[Crossbow]

You can't go that far. Consider RS485 which can run to 500 meters via an FCC left side adapter. The option board is only rated for 100 meters.

[Theo V]

Hello all, Thanks for all this input. I think I'll try the solution with two compact PLC's like Inntele advised with a RS485 connection trough separate left-hand modules considdering the note from Crossbow about the distance >100m. That means unfortunatly that I can not use the existing cables so the budget needs to be adjusted... :( Thanks a lot, best regards, Theo V. Edited March 1, 2015 by Theo V

[Inntele]

TheoV, if you have to build a new cable line, as alternative I can propose you to use a NB PLC modems: 1) It will allow to use the existing unshielded cable lines for RS485 communication; 2) It will allow to use cheaper FX**-485-BD boards instead of expensive FX3U-485ADP+CNV-adapters. So you can save money. I'd recommend this product http://www.gridcomm-plc.com/gc9200. Here you can find the contacts http://www.gridcomm-plc.com/contact_us/europe_sales_contacts. Just can not say, is able this solution to transfer N:N protocol, or not. With Modbus it will work exactly.

[Theo V]

Thank you Inntele for this Gridcomm equipment link. I see that they also have a sales representant in the Netherlands. I had some good results with the brand 'ADAM' and Westermo to extend the RS485 to a Scada computer over a long distance in the past too. I look into it. Best regards, Theo V.

[Inntele]

TheoV, if you look to the side of 'ADAM' and Westermo, then no problem. But products of abovementioned companies just allow to increase the communication distance via a shielded twisted pair, while I advise you the equipment, which allow to build RS485 network via an existing unshielded not twisted pair, i.e. the via the cable, that you planned to use for remote I/O control ... The N:N-network works fine with this modules: http://www.modemtec.cz/en/products/plc-modules It's checked.

[Theo V]

Hi Inntele, True, I only have a schielded 12x1mm2 cable not twisted pair available and Adam uses twisted pairs only. Today I checked out an other option, re-locate the PLC cabinet to the new engineroom and nearby the frequency inverter. That way I can start the other motors just with a contact from a local relay to the softstarter using the existing cable. This way I can be cost effective and save me a lot of headache with the connections. Only trouble would be the connection to the Scada computer but that is only 75m from the new engineroom. That should work with a RS485 left hand module and there is a cableway to that office. Thanks to all who helped me with good ideas, I really appriciate this! Beste regards, Theo V. Edited March 3, 2015 by Theo V

[Inntele]

The narrowband powerline modems should help you in it It even allow to communicate with Mitsu PLCs using Programming Tool Protocol, which is time critical to the responce. At 9600 Baud all works fine, I tested it and moreover have made several projects, that based on powerline communication and contol the train pushers, each of which is equipped with two 75 kW VFDs, via three-phase trolley powerline. In that applications I used N:N-network, which transfer via powerline.

[Theo V]

Hi Inntele, Thanks again. 9600 Baud should be more than enoug to communicate to the Scada computer. If the standard FX3U-485-ADP-MB module isn't working I wil look in this modem option as an alternative. Best regards, Theo V.