S7-300 and Danfoss drive FC300

Jethro Baidoo

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J
Join Date
Jun 2015
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Accra
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I want to read voltage and current from a Danfoss drive FC300 with S7-300 PLC.
I need help with the programming. Hardware bit has been done by OEM.
 
I know nearly nothing about Siemens PLCs so I am going to assume that Modbus RTU protocol can be made available.

If the drive is new it should support Modbus RTU protocol.

Google "danfoss fc 300 manual" and download the pdf.

Search the file for "Modbus" and you will jump to the area where it explains how to set up the VFD for that protocol.

Most VFDs (not sure about this one) will require that you cycle power after making changes to their serial port settings.

There are option modules for Modbus TCP, Profibus DP, Profibus, Ethernet IP, and DeviceNet to give you other options if the built in VFD serial connectivity is not practical for your application.
 
Hello Jethro;
You have selected PPO 4 as a telegram format, which gives you a total of 12 words in and 12 words out between the CPU (Profibus master) and the drive (Profibus slave).
Of these 12 words, 1 is reserved for the control word/status word, another for the speed reference/actual speed. That leaves you with up to 10 words (designated as PCD) you can read from/write to the drive; you do this by assigning to each PCD word (in- drive to PLC or out- PLC to drive) a specific FC 300 parameter.
The mechanism to select which values you can read from the drive to the PLC is called "PCD read configuration", and it is described in the FC 300 Profibus manual:
https://files.danfoss.com/download/Drives/doc_A_1_MG33C202.pdf

The screenshot below is a condensed view of the PCD read configuration. For motor voltage you must assign parameter 16-12 to a PCD of your choice, for motor current use parameter 16-14.
Hope this helps,
Daniel Chartier

Danfpss FC 300 PDC read.jpg
 
So that means with my current setup PCD3 will write to PIW660 and I will have to configure the danfoss drive parameter 9-16 to output Current(A) on PCD3.
Is this correct?
 
S7-300 & Danfoss

Hi dchartier,

As per Jethro fig(HW Configuration), there are only 6 words allocated (12 bytes).
12 Bytes are allocated for inputs & 12 bytes are allocated for outputs.

Bytes allocated are from 660 to 671

Best regards
 
Last edited:
I understand. But my question is since the first 2 PCDs(1 and 2) are reserved should I assume they automatically occupy PIW660 and PIW662 and that PCD3 will occupy PIW664?
 
Jethro Baidoo said:
I understand. But my question is since the first 2 PCDs(1 and 2) are reserved should I assume they automatically occupy PIW660 and PIW662 and that PCD3 will occupy PIW664?
Click to expand...

Yes.
After mapping your data out of the drive ,
You should be able see your mapped data from piw664



But there’s probably an sfc14/15 that reads and writes to a data block
(Already in your program)
 
Last edited:
Lets keep it simple
Do you see your unscaled value (drive voltage from the drive) in piw 664?

In a vat table…
 
Last edited:
JRW said:
But there’s probably an sfc14/15 that reads and writes to a data block
(Already in your program)
Click to expand...
+1

Notice that the drive type description is "PPO Type 4 Module consistent PCD" and there are 12 Bytes in both directions.

Either, the IO addresses for the drives are inside the process image of the S7 CPU, and then you can just use the IW and QW addresses.
Or, the OP addresses are outside the process image of the S7 CPU, and then there should be SGFC14/SFC15 (DPRD_DAT/DPWR_DAT) blocks in the program to transfer the IO data to/from a DB.
Since there are so many drives, it is most likely the latter (SFC14/SFC15).

Notice, you cannot merely access the IO addresses with PIW and PQW instructions. The drives needs the entire control data set to be consistent, which it is not if you write and read individual words.
The drive will probably report a comms fault if you try to do that.
 
Last edited:
You have to setup the FC300 drive to send the data as decribed by dchartier. I dont know Danfoss drives.

SFC14/SFC15 merely transfers the data from the Profibus IO addresses to/from a suitable DB.
 

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