control unisab by PLC

[frigofer]

hi guys!

i have a question: is it possible to control a unisab III via plc? i know i can connect a plc to read the values, statistics etc.. but can i send comands from a plc to the unisab? in particular i would like to tell the unisab how much power i need on the output and he then regulates the slide and the inverter accordingly. i would need that the PLC takes the decision of how much power the compressor has to output and not the unisab. the unisab should only decide the rpm and the position of the slide.

thanks

best regards

frigo

[Segei]

I'm not familiar with unisab, but many compressors have 3 settings to control capacity:auto, manual and remote. Probably, unisab has remote control as well.

[Josip]

Hi, frigofer :)


hi guys!

i have a question: is it possible to control a unisab III via plc? i know i can connect a plc to read the values, statistics etc.. but can i send comands from a plc to the unisab? in particular i would like to tell the unisab how much power i need on the output and he then regulates the slide and the inverter accordingly. i would need that the PLC takes the decision of how much power the compressor has to output and not the unisab. the unisab should only decide the rpm and the position of the slide.

thanks

best regards

frigo:)

Yes it is possible .... but..

first I would like to ask you something ...

.... why do you need that your PLC (and not Unisab) takes decision about output power, what is your idea and why?


Best regards, Josip :)

[frigofer]

there are several reasons... i'm not the one who will set this in place, i have only been told to find out if it is possible. i dont understand a thing bout refrigeration.. XD

i think the reasons are:
-if the master sab is beeing changed or repaired or whatever the other will still work fine
-give priority to certain machines (for example if we know that in a year a machine will be changed for a newer system then it could be good to let this machine run more often witha higher priority)
-have a centralized system and logic to control everything
-more control over the system
-connect the compressor control logic with the logic of other parts of the system to avoid short startups if not needed.

as said, i am not the one who follows this, so these are just my guesses.. i might be 100% off..

[mark957]

http://www.sabroe.com/fileadmin/filer/pdf/Brochurer/Controls/Controls_Profibus_10_1_.03.04.pdf

[Josip]

Hi, frigofer :)


there are several reasons... i'm not the one who will set this in place, i have only been told to find out if it is possible. i dont understand a thing bout refrigeration.. XD

i think the reasons are:
-if the master sab is beeing changed or repaired or whatever the other will still work fine
-give priority to certain machines (for example if we know that in a year a machine will be changed for a newer system then it could be good to let this machine run more often witha higher priority)
-have a centralized system and logic to control everything
-more control over the system
-connect the compressor control logic with the logic of other parts of the system to avoid short startups if not needed.

as said, i am not the one who follows this, so these are just my guesses.. i might be 100% off..


It is possible to control UNISAB III if you use User input regulator (input 4-20mA) depend how you want to have control on ... suction, brine temp-chiller, discharge pressure, process out (hot water), capacity ....

then you can make a network with up to 14 UNISAB III/UISAB II where you can set up which compressor you want like a master then via PC you can change your User input values ...

What I can say UNISAB III is extremely powerful to operate refrigeration compressors, both, screw/piston, conventional or rotatune/inverter ... to utilize a full power of UNISAB III for user is most important to make a fine tuning of PID/P regulator, timers, pressure transmitters calibration, set up the right working temperature and pressure, alarm values ... this unit is designed to control refrigeration compressors with many integrated limiters to reduce capacity during some period when compressor is out of envelope values without stop etc. ....

Of course, you can use PC to control other parts of your system and use your feedback for external start permission .... It has so many possibilities what is very hard to explain in short...

to control your compressors i.e. refrigeration system you have a tool, just need to learn, how to use it in the best way...



Here is one good link to Sabroe: http://www.sabroe.com/products/controls.html


Best regards, Josip :)

[piewie]

Unfortunately the UNISAB III is not as robust as the UNISAB II and is a lot more finnicky I think it is too do with the fact that we have been given too many choices and also Yorks need to distance itself from Danfoss has lead to a more comercial type product similar to what is being output into the chiller market. But saying all that it has become better at communicating with PLC's. You are really looking at a high level type interface and to get the best results you will need to interface with a Profibus network card on the PLC side. Both Siemens and Mitsubishi have the ability to do this for you and the blocks that are needed for the coding are available from Sabroe. The connection to the UNISAB II is quite simple as it only needs the wire terminated into terminal block on the board the UNISAB III is a little more complex as you need to purchase a seperate Profibus termination plug/block. I have not worked on them for about 18 months now but back then there were some issues with the Mitsi Profibus coding blocks. These should have been sorted out by now but for me then it was a little bit of experimenting. If you have a field of UNISAB II's and UNISAB III's then I would suggest keeping them on seperate networks. Another item of great importance is keeping a register of all the setup parameters for each compressor I cannot emphasise how important this is. On the UNISAB III this is quite easy as the information can be uploaded/dowloaded via the memory card. SABROE also have a small EXCEL program that can assist with this. Once again it is very important that you keep track of the software versions etc. THe last project I worked on we used Mitsi PLC's and we only used the Profibus to output operating data into the SCADA I did start working on a high level interface programming strategy to increase the energy performance etc but then I came across a few problems with the coding blocks. SABROE were busy sorting this out but my time ran out and I moved to Australia. If you want any further information I will be glad to help I could also send you some mitsi programs that we developed if you like.