mvanbergen

Hi all,

I am in the midst of a control systems upgrade that involves Modbus serial comms to a Bently Nevada 3300 vibration monitoring system.

I've found in the system manual the following detail:
"Internally the Serial Interface converts the backplane multiplexed static data signal into a digital value using an 8-bit analog-to-digital convertor. When an analog data request message is received on Modbus protocol, this 8-bit value is shifted left 4 bits to represent a 12-bit value. Since the maximum value the 8-bit convertor can have is 255, then the maximum 12-bit value is 255(16) = 4080. The least significant four bits of the 12-bit binary word are always zero."

The Modbus function code reads this in as a 16-bit integer though - so what happens to the other 4 bits? Are the most significant bits zeroed, giving the actual original 8-bit word (0-255) in the middle of the 16-bits? Or the least significant bits, giving the last 8 bits all zeroed and the actual original 8-bit word (0-255) all in the most significant byte? If the signal going into the converter is scaled -40mm to +40mm, how would the conversion back to EU be done when it arrives as a 16-bit integer?

Appreciate any experience anyone has with this.

Thanks,
Michael

ControlsGuy25

Hi all,

I am in the midst of a control systems upgrade that involves Modbus serial comms to a Bently Nevada 3300 vibration monitoring system.

I've found in the system manual the following detail:
"Internally the Serial Interface converts the backplane multiplexed static data signal into a digital value using an 8-bit analog-to-digital convertor. When an analog data request message is received on Modbus protocol, this 8-bit value is shifted left 4 bits to represent a 12-bit value. Since the maximum value the 8-bit convertor can have is 255, then the maximum 12-bit value is 255(16) = 4080. The least significant four bits of the 12-bit binary word are always zero."

The Modbus function code reads this in as a 16-bit integer though - so what happens to the other 4 bits? Are the most significant bits zeroed, giving the actual original 8-bit word (0-255) in the middle of the 16-bits? Or the least significant bits, giving the last 8 bits all zeroed and the actual original 8-bit word (0-255) all in the most significant byte? If the signal going into the converter is scaled -40mm to +40mm, how would the conversion back to EU be done when it arrives as a 16-bit integer?

Appreciate any experience anyone has with this.

Thanks,
Michael
Hi

Sorry for late response..
Can you update on this case..
We will be better position to support..

mvanbergen

Hi,
Thanks for the reply - we haven't progressed any further at this stage. I expect we'll have to play with the configuration once the comm link has been moved across to the new PLC, but was hoping to have some more insight before getting to that point.
Thanks
Michael

ControlsGuy25

Hi

I will get a closer look on this thread and come back ..

Thanks
James

ControlsGuy25

Can you share a topology/architecture of the installed system ...

WE need to know what devices are interconnected and will try to get a modbus map for the dedicated devices communication