Hi,

We are using two Hydrovar VFDs (Model - HVL44.022-A0010) for a booster system. What I need is to give below pump status
1. Pump Run,
2. Stop,
3. Trip and
4. Actual (running) frequency to the BMS system. (We will not be doing the BMS part.)

But when I connect the vfd to pc via rs485 converter and check the inputs by modscan, it's showing that
"modbus exception response from slave device" and sometimes "MODBUS Message TIME-OUT"

I am new to this communication field. What is the issue here?

This is the modbus communication manual for the VFD
https://www.xylem.com/siteassets/brand/xylem/hydrovar/hvl_modbus_manual_rev.bed01_2018_en-us.pdf

 

An exception response means that the device is responding with an error code. However, the fact that the device is responding (even though it is an exception code) does mean that your communication settings (baud rate, parity, address, etc.) are correct.

You are probably accessing registers that do not exist on the unit. Review the register list in the Modbus documentation you linked. It appears the first register (for STOP/START) is register 49. Try entering 49 for the Address in ModScan and enter 1 for the Length. If that works, you can try increasing the Length to 3 (as the register list defines registers 49 - 51). If that works, you can move on trying to increase the length further, however, this may or may not work as the next defined register after 51 is 55 (i.e. registers 52 - 54 are not defined). Some Modbus slave devices allow reading undefined registers, while others will return an exception response if any undefined registers are included in the range of registers requested.

 

If the value at register 49 is a floating value then you'll need to enter 2 for the Length.