|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. Please remember that the holding registers are actually zero-based, so when programming a “one based” Modbus master, you need to add “1” to the register number to read the correct register. When using Modpoll, you should use the argument “-0” in the command line.
2. Holding register table
VPSensorCartridge connection status
|Modbus return value||Description|
|0||No VPSensorCartridge connected.|
|1||VPSensorCartridge is connected.|
|2||VPSensorCartridge is connected, but not sufficiently (>12v) powered.|
|3||VPSensorCartridge error; contact local distributor / VP Instruments.|
Analog output unit enum
Table van pagina nummer 34
3. Modbus settings
The Modbus settings can be changed with VPStudio , with the keypad of the Transmitter when available. Below all available options are given:
- 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 has an integer multiplier option. With this option, you can multiply the outcome to get a more significant output.
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 C5 we show how to change your Modbus settings.
Function code 0x03 for reading (Holding register).
Function code 0x06 for writing a single register (Holding register).
Function code 0x10 for writing multiple registers (Holding register).
The data format is in little-endian.