Modbus

[VigneshGunasekaran]

Hi

Did any one used Contrec Heat Calculator Model 212, using Modbus Communication for reading data. I cant able to read data. I dont know where i am wrong.

How to check what is the problem whether there is address mismatch or anything. Currently i am using Modscan for testing.

 

[danw]

- The exact problem is? Are you reading data of the wrong value or no data at all?
- Can you provide a link to the Contrec documentation with Modbus communication details?
- the physical link you are using is? RS-232? RS-485? ethernet?
- if serial, your serial settings are . . . ? If ethernet your IP addresses are ? ?
- what is the error code Modscan is providing? no connection? Modbus error?

 

[VigneshGunasekaran]

Hi
Now i can read some value in the register 26,27..etc
in register 26 i am getting (F4241)H and in register 27 (47DC)H.
In the energy meter i am reading 113124.5kwh.

I am using RS485 RTU. I have attached energy meter details also.

 

[danw]

from page 42 (pdf) of Model 212 manual:

Read Only Registers
Address Name Value Note
25 Energy 0 FP
27 Energy 1 FP
29 Accumulated energy 0 FP
31 Accumulated energy 1 FP

from page 40 (pdf)
Conventional numbering of registers often starts from 1, therefore be aware that "register 1" in this case has an "address 0" and so on.
------------

FP means floating point. Modscan will read values in different formats. Instead of reading the value in hex, read it in Floating point. Note that the 5th button from the left (sligthly depressed) brings up the legend "Floating Pt." when the cursor is passed over the button.

[/IMG]

Your meter reading in units of kwh is a totalized value which would come from addresses 29 & 30 (for accumulated energy 0) and 31 & 32 (for accumulated energy 1).

I assume that energy is the instataneous reading in kW.

 

[VigneshGunasekaran]

Hi

Pls find the attached screenshot. whatever the value i am getting is correct.

But how to convert two Hex resisters to float value.

 

[danw]

Your problem is not "Modbus".

Your screen shots show that the Modbus connection is working and you're getting the data. Modscan is doing the conversion from "bits in a register" to either hex or floating point.

You need to assess what format your PLC will use in handling the incoming data. As raw Modbus it is 'bits'; your PLC might be dump raw bits into byte formatted words, or it might have conversion routines to convert to other word formats, like floating point.

So restated, your problem is "converting raw Modbus data to whatever my PLC handles (specific format for your PLC and its ability to handle data formats and do math internally).

I can't help you with that. I'm not a PLC guy.

You asked about a conversion to floating point. Are you sure your PLC can handle floating point?

 

[HAROLD]

have you tried "swapped FP" data type....for devices that put floating point values in registers in "word reversed" format

 

[VigneshGunasekaran]

Modbus with L45

Hi

Now i am facing one more problem. I can able to establish modbus communication using modscan.

But with the same parameter if i try with CompactLogix L45 using 1761 NETAIC, i couldnt able to do.

What may be the problem.