Siemens ModbusTCP To Sentron Power Monitor

[rtgibson]

At my wits end.....I have a Siemens S7-1200 and a Sentron PAC3220 Power Monitor. Got the MB_Client command to connect and work in TIA 15.1 but I only seem to be able to pull back the first 9 variables (voltage & currents (Page 113 in Sentron manual) 18 registers/36 Bytes worth. If I try to pull anymore back the block freezes up and I start getting errors - Yet I can change the start/offset address and read 36 bytes worth from further down the variable list.

I've slowed the poll time right down and it makes no difference, is there a limit on how much data can be read ?

Thanks
Russ

 

[tragically1969]

At my wits end.....I have a Siemens S7-1200 and a Sentron PAC3220 Power Monitor. Got the MB_Client command to connect and work in TIA 15.1 but I only seem to be able to pull back the first 9 variables (voltage & currents (Page 113 in Sentron manual) 18 registers/36 Bytes worth. If I try to pull anymore back the block freezes up and I start getting errors - Yet I can change the start/offset address and read 36 bytes worth from further down the variable list.

I've slowed the poll time right down and it makes no difference, is there a limit on how much data can be read ?

Thanks
Russ

Modbus should be able to read 125 registers in one block read BUT they have to be contiguous, is this the case with the first 18 registers in the meter ?

 

[danw]

The maximum number of contiguous registers that can be read is device dependent. The Modbus spec limit is 125, lots of devices have limits much lower than the Modbus max.

I did a quick scan of a PAC3200 manual dated 2008 and found no limits on FC03 read operations.

There are warnings that a read that starts at the 2nd register offset value of a floating point value or a read that stops at a register value that only gets half of a float will fault as an error. The process variables are all floating point values so your FC03 read poll should asking for an even number of the quantity of registers; an odd quantity will cause a fault/error message.


If it were me, I'd use my generic Windows Modbus Master/client Modscan to see whether Modscan can fetch more than first 9 variables. If Modscan can fetch more than nine, then it's a TIA issue. If Modscan can not fetch more than nine, then it's a PAC3220 issue.

 

[rtgibson]

Thanks for the responses.

It is one continuous block that I'm trying to read.....I got a little further, for no apparent reason rather than adding a chunk of extra variables I started to add them just one more at a time and it would work. Then randomly I'd add another and it would error......take it off and wind it back and it would work again....then add the same variable in exactly the same manner (repeating what I'd done a couple of steps ago) and it would work. Eventually I did this adding, sometimes deleting and adding again and finally topped out at around 44 variables. For the rest that I needed I used a second MB_Client instruction to the same device but set to start at a different offset and grabbed a few more that way.

It works for now but seems well ropey. And the worst part is I don't know why its working.

Russ