How to use a FIT controller to control a Variable Speed Drive via modbus communication.

Below we will guide you trough the process of using a FIT controller for controlling a VSD. But also provide you with additional information to explain the parameters. This guide does not go into drive specific details and is intended to gain a general understanding of this feature. An example of a FIT controller operating with a Delta, VFD-M drive via modbus communication is available in this article . To gain a better understanding how to apply drive modbus documentation to the configuration of the FIT controller, consult this article.

General

Set 'Starter mode' P10.01 to VSD

This enables the inverter drive control function.

Set 'Control mode' P10.02 to Pressure sensor

The VSD function is only available when the controller is in a 'Pressure Sensor Mode'.

Digital output (R5) can be used to start and run the inverter drive (safety hardwire link).

Example wiring diagram of a FIT controller, connected to a VSD

FIT parameters to be configured (P08 - VSD Configuration)

Multiple parameters, related to the functionality of the variable speed regulation can be selected here. For more information on each parameter, please consult the FIT controller manual. The crucial parameters for a correct VSD operation are described below.

P08.08 - Ouput

A speed signal can be sent in 'Hz' or in '% load'. Which value to select, depends on the used VSD speed register type.

P08.09 - Slave address

The VSD will "listen" to the commands of the FIT-controller. And is therefore called a modbus slave. For the FIT controller to know where to send his commands, he needs to know the address of the VSD. The VSD address set in the VSD and the FIT controller need to match to be able to communicate with each other.

P08.10 - Speed Register

The VSD will save, or hold the speed value in a specific register. Writing a value to this register allows the FIT controller to regulate the rotation speed of the attached motor. The FIT controller needs to know where to write this speed value.

P08.11 - Parity

The parity type is part of the configurations of the modbus protocol. The parity set in the VSD and the FIT controller need to match to be able to communicate with each other.

P08.12 - Baud Rate

The Baud Rate is part of the configuration of the modbus protocol. The Baud rate set in the VSD and the FIT controller need to match to be able to communicate with each other.

P08.13 - Fault Register

A drive fault can be "detected" via 2 different register.

A general drive fault register.

This register contains a value that can be used to detirmine the current active fault on the VSD.

A status word register.

When a fault is present on the VSD. A status flag will be set high (1).

P08.14 - Fault Bitmask

By applying a bitmask, the FIT controller knows which bit(s) to take into consideration to determine if a fault is active on the VSD or not.

P08.15 - Reset Register

A drive fault can be resetted by writing a certain value, most often in the form of a high flag to a certain register.

P08.16 - Reset Bitmask

By applying a bitmask, the FIT controller knows which bit(s) to set.

Every time you attempt to establish a connection, active faults on the FIT controller have to be cleared. The communication will only be initialised between the 2 devices after this attempt of clearing active faults.

Drive parameters to be configured

To establish a correct connection between the FIT controller, and the drive, there are also a couple of parameters that have to be configured on the drive itself. Some general parameters are described below.

'Speeds reference' to be pointed towards the desired 'Speed register'.
'Speed reference source' to be activated and listening to a RS-485 (modbus) communication.
Drive maximum speed.
Drive minimum speed
Address
Baud rate
Parity
Communication protocol: Modbus RTU (8 databits, 1 stopbit)
Communication mode: Modbus

On a lot of drives, a power cycle is required to save the made changes to its parameters. If you forget about this step, the parameters between the FIT and drive will never be synced.

C ommon erros & solutions during commissioning between Master (FIT) and Slave (Main drive)

Fault Code	Fault description	Cause	What to do
S3502	Controls Studio Session Active	A connection between CS and the FIT controller is active.	Ater finishing the parameters' configuration/transfer, click the disconnect icon in the CS interface.
S3601	No Main Drive Communication	After setting the starter mode P10.01 from the default 'M/S/D' to 'VSD' via CS, this alarm will be activated automatically when no valid communication is established between the VSD and the FIT controller.	Both the hardware connection, and the communication protocol have to be configured / set-up correctly. Check integrity of the coms cable. Check polarity of the coms cable. Check integrity of the used communication ports on both controller and VSD side. Check fault E0605 to troubleshoot the software part. When an incorrect register is inserted in the configuration, it will trigger an exception response. This exception response can interrupt communication. Re-evaluete the used registers. Using a RS485 analysing tool can help.
E0605	Drive Communication Error-Main	Parameter settings inconsistent or not compatible with selected protocol.	The communication parameters have to be equal (synced) between both devices. -Check the status of the main drive.(online/offline/error etc.). -Check the main drive comms' protocol selection <Modbus RTU> -Check slave address. (FIT default: 1) -Check baud rate. (FIT default: 57600) -Check comm. format. (FIT default: 8,N,1)
E0607	Drive Comm. Exception-Main	A timeout has occurred in the comm. period,between the FIT and the main drive.	- Re-evaluate the set registers in the FIT controller. Sending a message to an incorrect register, can cause an exception response. - Check the main drive comm. time-out setting. - Check the source of frequency command on main drive.
E0609	Drive fault-Main	There’s an active fault with main drive.	Please check and solve the main drive fault code refer to the main drive manual accordingly. If no fault is active on the drive, re-evaluate the register and/or bitmask used to read the drive fault. Reading an incorrect register can cause the FIT to believe a fault is present, even tho there might not be.

Fault code categories:

S/R/L .... Start, Run or Load Inhibit; self resetting

A .... Warning; manual reset

E .... Fault (Shutdown, Immediate Stop); manual reset

Getting a VSD up and running correctly is no easy task. It is strongly recommended to consult the drive manufacturer during such a set-up. Although CMC NV is happy to help, providing support in such situations is difficult and limited. We are unable to judge how you would like to control/operate your drive.