1756-OF8 Current Output

[wsy_nte 0]

I have application that using 1756-OF8, I want to use five channels (4-20 mA) as speed ref to five DC drive. Could we do this? Any idea or suggestion? Thank you. James

[TimWilborne 108]

You can as long as you analog reference isn't used to reverse the drive. See if specs of the drive say -20 to 20 mA. If it is -20 to 20 mA then it will not work because the the 1756-OF8 will only do 4-20ma. But it will do -10 to 10 volts so if you need to reverse off of the analog input see if the drive will accept a voltage command

[wsy_nte 0]

I use forward operation, the specification if 4-20 mA. I will used single ended connection for five drive using five channels.

[wsy_nte 0]

The drawing of 1756-OF8. Thank you for any comment or suggestion 1756_OF8.doc

[Contr_Conn 4]

I already answered the same question from the same person in this post: http://www.plctalk.net/qanda/showthread.php?t=19576 I just don't usderstand what is your question? Can drive speed reference be controlled from the OF8? - Yes. Can output be set to current? yes. Module has 8 channels in single mode, so all drive commons will be connected. If commons must be separate, use 1756-OF6CI isolated module

[TimWilborne 108]

Perhaps James is just trying to learn about general drive control and measurement. He has asked about the 1769-HSC, the 1756-HSC, and now the 1756-OF8. James is this a single project or multiple projects? If this is a single project that you are trying to spec out could you layout the details of what it must do? Maybe we could help you come up with a solution. If these are multiple projects or you are just trying to learn, please continue to ask your questions. That is the best way for all of us to learn.

[wsy_nte 0]

Thank you for reply. 1769-HSC I just to learn using 1769-L32E processor, this is new to me. I have single project with 1756-HSC and 1756-OF8. We use encoder to measure the motor feedback rpm and using emerson ES2300 dc drive. We using PID to control motor speed, speed ref will connected to emerson drive pin 32 and 34 (speed ref- signal 4-20 mA). We connect 5 drive to differenc five channels on 1756-of8 (single ended connection). I want to know that this connection will ok to control the motor speed. This is basic knowledge of analog connection. Any idea or suggestion? James

[TimWilborne 108]

You should be fine hooking all 6 drives to one OF8. With 4-20mA your commons shouldn't even be that much of a concern but I would still hook all of the speed reference commons together

[darrenj 0]

I haven't had much luck with non isolated outputs controlling multiple drives..Let the magic smoke out of one of them..:( I now always use a loop isolator just to be safe..I use a wiedmuler (Sp?) and it cost about $130..Multiple configs..0-20 4-20 -10-+10 input to all of the same output.. New board for obsolete drive..priceless loop isolator $130.00 I learned my lesson!! Edited 4 Jan 2006 by darrenj

[Ghettofreeryder 0]

I currently look after 6 sites which have vfds being controlled off of non isolated analog outputs. We havent had a single problem with them. The smallest site has 4 yaskawa F7 drives, while the largest has 12. Havent let the factory smoke out yet. U should be fine with your configuration.