Using PID over RS485 with S500 Drive

[Kings and Barnhams Automation]

afternoon guys and girls, i would greatly appreciate some advice on a project i am working on. the scenario... using a 4-20mA pressure traansducer to control an S500 using PID. that bit is fairly easy, however.... im trying to do this via an FX3U and over RS485. i have the inverter talking to the PLC on RS485. i can issue run commands and manual speed commands ok. now i am using an analogue input card to receive my 4-20mA transducer, and an analogue output to send a 4-20mA signal to 3 seperate drives. following so far.... what i need to know is how to issue a PID set point on the drive. normally you would use P93 but im not convinced the drive is looking at P93 in computer link mode. im using IVDR instructions to issue operation commands to the drive and i have tried writing to P93 using an IVWR instruction (which does write to P93). at the moment the drive tries to run but it seems as though the PID set point is too low and the drive is ramping up very very slowly. hopefully someone will be able to understand how ive written this! many thanks in advance, Rob

[Kings and Barnhams Automation]

ok, slight update. i can set the PID set point using a potentiometer across terminals 2,5 and 10 on the inverter drive. i suspect this is because i have set parameter n9 on the drive to 1 for an external speed reference. so this leads me to the question of how to program a PID set point over RS485 so i do not have to wire a pot to the drive? thanks, Rob

[Crossbow]

Make sure the number you are sending is in the right range for the parameter. Your PID loop might be creating too small of a number.

[Kings and Barnhams Automation]

ok that makes sense. i can send a value to P93 of say 30% so in theory the drive should be looking to keep 8.8mA as the PID value. but the drive still doesn't seem to respond to this. however, it will work with a pot setting the PID set point manually. the key parameters i am setting on the S500 are: P79 - 2 P88 - 20 P89 - 100 P90 - 1.0 P91 - 100 P92 - 0 P93 - 30.0 P94 - 1.0 n8 - 0 n9 - 1 n10 - 1 this is allowing the drive to start in computer link mode and then the frequency is set via a 4-20mA input across terminals 4 and 5. i am starting the drive using the command IVDR K1 H0FA H3 K1 in my FX3U (STF command and AU enable) i have also put a physical link between PC and RL and set P60 to 14 (enabling PID control) The PID does seem to work, but only when i adjust the set point using a pot across terminals 2,5 and 10 i just dont know how to change the PID set point using code (so it can be changed by a HMI) thanks, Rob

[Veganic]

Try P79 -3? p93.bmp

[Kings and Barnhams Automation]

Try P79 -3? the problem with changing P93 to 3 is that the drive wont start up in computer link mode maybe you cant set the internal PID set point in the config i have, but i find that hard to believe. is there any way of sending a 4-20mA signal to the drive over computer link? this way i could drop the physical external 4-20mA signal to the drive. this should allow me to change n9 back to 0 and then P93 should become active? i hope someone can understand what i am saying, it makes sense in my head! failing this, can the problem be overcome by using an F700, as this is the actual drive i will be using for the final application (s500 is just a test drive i have but the code should be very similar) thanks Edited November 7, 2008 by Kings and Barnhams Automation

[swimmy67]

Here are the parameters that I set for communicating with a FX2N or a FX3U PLC. See attached immage. Edited November 7, 2008 by swimmy67

[Kings and Barnhams Automation]

any more ideas guys? i cant believe that this cant be done

[Kings and Barnhams Automation]

update time... ive changed the drive to an F700 and i can now get the drive to act on PID and change the set point without the need of a pot. still dont no why i couldnt do this using an S500. next question: which instruction or set of instructions do i need to monitor the PID process value of the drive in my PLC? looking at the (very poor)F700 manual, it seems to be that i need to use instruction code H72 or H73 in conjunction with special monitor selection H35. the problem i have is which instruction do i need to make this work? IVCK, IVRD etc. do many people have problems with their mitsi support? cheers

[Crossbow]

IVCK looks at monitor data in the drive. IVRD reads parameters. The manual is pretty clear on this. If it's monitor data, I would expect you are using IVCK. Manual JY997D16901 from www.meau.com covers the inverter commands in great detail. I assume Mitsubishi UK has the same manual, though not sure if they use the same number.

[Kings and Barnhams Automation]

in my opinion the mitsi manuals are very poor. ive always had this criticism but that is besides the point. and yes i know that IVCK monitors data and IVRD reads parameters. this may well be clear, but special monitor selection numbers arent. however, i have figured out how to do this, and if anyone is interested the code is: IVDR K1 H0F3 H35 K1 moves PID process value to HF3 IVCK K1 H72 D108 K1 reads special monitor as 4 digit output for reference, to monitor the output frequency you need this code: IVCK K1 H6F D108 K1 so you can see that reading the frequency is easy, but the special monitor is more complex, and i dont think the manual made it any easier. cheers

[Veganic]

Was this what you were trying to do? Can I give in S500 PID application STF+PID Set value with RS485 communication and read actual value with analog input 4? (500 series (S,E,F and A)) - KS01162 Yes this combination is possible. Please see attached document. read more Yes this combination is possible. Please see attached document. http://78.136.49.242/branch/database/sendf...mp;m_culture=en A bit late I know.