1. Introduction
 | Before you start, familiarize yourself with RS485 networks and the Modbus protocol basics. |
Since RS485 networks and the Modbus protocol are typically understood only by trained technicians, we refer to chapter G9; for more information on the communication protocol, definitions and additional resources for training.
In Modbus devices, the actual measurement data is placed in holding registers. To readout this data, you will need to use the corresponding holding registers which are given in the next table. All data is stored in two 16-bit registers with below register number as a start address. Read out the data with this start address and length 2.
2. Holding register table
| Decimal | HEX | Description | Type | Read / Write |
| 16 | 0x 10 | Flow in mn/sec | 32-bit integer (x10) | Read |
| 17 | 0x 11 | Flow in m3n /hr | 32-bit integer (x10) | Read |
| 18 | 0x 12 | Flow in ln /min | 32-bit integer (x10) | Read |
| 19 | 0x 13 | Flow in SCFM | 32-bit integer (x10) | Read |
| 20 | 0x 14 | Flow in m3n /min | 32-bit integer (10x) | Read |
| 21 | 0x 15 | Flow in sfps | 32-bit integer (10x) | Read |
| 32 | 0x 20 | Pressure in bar | 32-bit integer (10x) | Read |
| 33 | 0x 21 | Pressure in psi | 32-bit integer (10x) | Read |
| 64 | 0x 40 | Temperature in oC | 32-bit integer (10x) | Read |
| 65 | 0x 41 | Temperature in oF | 32-bit integer (10x) | Read |
| 128 | 0x 80 | Totalizer in m3n | 32-bit integer (10x) | Read / Write* |
* Writing to the totalizer will reset the totalizer to zero.
| Decimal | HEX | Description | Type | Read / Write |
| 8 | 0x 08 | Diameter | 32-bit Floating point | Read / Write |
| 9 | 0x 09 | 4 .. 20mA Max | 32-bit Floating point | Read / Write |
| 10 | 0x 0A | 4 .. 20mA Min | 32-bit Floating point | Read / Write |
| 11 | 0x 0B | 4 .. 20mA Unit | 32-bit Floating point | Read / Write |
| 24 | 0x 18 | Flow in mn/sec | 32-bit Floating point | Read |
| 25 | 0x 19 | Flow in m3n / hr | 32-bit Floating point | Read |
| 26 | 0x 1A | Flow in ln /min | 32-bit Floating point | Read |
| 27 | 0x 1B | Flow in SCFM | 32-bit Floating point | Read |
| 28 | 0x 1C | Flow in m3n /min | 32-bit Floating point | Read |
| 29 | 0x 1D | Flow in sfps | 32-bit Floating point | Read |
| 40 | 0x 28 | Pressure in bar | 32-bit Floating point | Read |
| 41 | 0x 29 | Pressure in psi | 32-bit Floating point | Read |
| 72 | 0x 48 | Temperature in oC | 32-bit Floating point | Read |
| 73 | 0x 49 | Temperature in oF | 32-bit Floating point | Read |
| 136 | 0x 88 | Totalizer in m3n | 32-bit Floating point | Read / Write* |
* Writing to the totalizer will reset the totalizer to zero.
Available write operations
You can also configure some parameters of the VPFlowScope DP / Probe and In-line via Modbus.
3. Modbus settings
The Modbus settings can be changed via the display and with VPStudio 2 you can change the options below:
- Hardware address: 1-247
- Integer multiplier: 1-1000
When the type of your Modbus is integer your output is rounded to the nearest integers. This will sometimes result in a less precise outcome. To get your output more precise VPStudio 2 has an integer multiplier option. With this option, you can multiply the outcome to get a more significant output.
Example:
The output of your temperature in Modbus is 33 degrees. You set your integer multiplier to 100.
The new output of your temperature is 3343. So actually the temperature is 33.4 degrees.
In chapter B6 we show how to change your Modbus settings.
Data format
Function code 0x03 for reading(Holding register).
Function code 0x10 for writing (Holding register).
32-bit Floating point Little-endian [CDAB]
32-bit signed Integer Little-endian [CDAB]
4. Next step
There are many ways to readout your VPFlowScope. Go to the next chapter to learn more about the real-time readout via VPStudio 2 software. The key for a long lifetime and reliable measurement results, it is key to service the equipment on a regular basis.
Next step:
- Service your flowmeter go to H. Service