Send floating point value between 2 Redlion Graphite HMI's

[Saint Germain]

I have 2 RedLion Graphite HMI's where one is communicating with some remote I/O using Modbus TCP/IP protocol. I have a second Graphite that will need to mimic the values from the first HMI, but using a protocol which supports a single twisted pair cable like Modbus RTU.

All of my analog input tags are scaling the values to floating point numbers. I do not think that I can transmit a floating point value over Modbus RTU, only integers. Is there a way to do this? Or is there another protocol that the Graphite HMI's support that I should use?

Thank you.

 

[danw]

Modbus is a protocol, a set of rules, that defines the rules for how data is transferred between master and slave and how the data bits are 'packed' for data transmission.

To Modbus, all data is just bits; the bits have no meaning to Modbus. Modbus rules define an input or holding register (used for data values as opposed to discrete on-off states) as 16 bits. But Modbus does not define how the data is represented in a 16 bit register.

It's up to the 'application', the firmware/software of the devices on each end, to interpret what the 16 bits in a register mean, or what value the combination of 32 bits in two registers is [32 bit floating point uses 2 consecutive 16 bit registers).

Hence, the Modbus spec does not define data formats; the device manufacturer implements a format and defines what the bits in a register (or multiple registers) represent. Hopefully the mfg describes in the documentation what their format is, what the units are and things like any multiplier needed to interpret the bits.

Modbus can carry all sorts data like

- a signed integer
- an unsigned integer
- real or floating point value
- time stamp
- model ID
- alphabet characters (text)
- whatever

as long as the devices at both ends can interpret the data properly.

The issue of data interpretation is the firmware/software tools that one has to interpret data.

Any industrial Modbus-enabled PLC is likely to interpret a Modbus input or holding register data as a signed integer, most handle one of 4 floating point formats, many handle alternative floating point formats, many handle long integers (32 bit integers).

From just a casual reading of threads on this forum, I believe that Red Lion devices can handle floating point values, whether the values come over Ethernet (Modbus TCP) or RS-485 (Modbus RTU).

 

[diat150]

I have 2 RedLion Graphite HMI's where one is communicating with some remote I/O using Modbus TCP/IP protocol. I have a second Graphite that will need to mimic the values from the first HMI, but using a protocol which supports a single twisted pair cable like Modbus RTU.

All of my analog input tags are scaling the values to floating point numbers. I do not think that I can transmit a floating point value over Modbus RTU, only integers. Is there a way to do this? Or is there another protocol that the Graphite HMI's support that I should use?

Thank you.

yes, one red lion can be setup as a modbus slave and the other as a modbus master, which you could then use to pass the data between each red lion. If you have the choice of using ethernet instead of a single pair between the red lions, you can use opc also.

Let me know if you need help on this, I am just down the road from you.