MODBUS

Based on MODBUS Application Protocol Specification V1.1b3

This capability is provided by LiveRig Collector 2.28.0 or higher

Modbus is a serial communication protocol developed by the Modicon corporation (now Schneider Electric) in 1979

It is an open communication protocol to interconnect electronic devices such as:

  1. PLC's (programmable logic controllers)

  2. Sensors

  3. Monitoring equipment

  4. Actuators

  5. IoT devices

  6. Supervising systems

Modbus protocol is able of receiving data from any industrial equipment devices that uses TCP and Serial (RS-232 or RS-485) connections.

Modbus data

There are a number of memory areas defined in the Modbus specification as described below:

  • Discrete Input (Read Only) - Boolean input value, usually representing a binary input to the PLC

  • Coils (Read / Write) - Boolean value, usually representing a binary output from the PLC

  • Registers

    • Input Register (Read Only) - Short input value, usually representing an input to the PLC

    • Holding Register (Read / Write) - Short value, usually representing an stored input or output

NOTE: All memory areas described below is Read Only for LiveRig Collector

For defined types in memory areas (e.g. double, long, integer, boolean) check modbus.json for configuration.

Configuring connection for Modbus sources

Modbus in LiveRig Collector can be accessed by two kinds of transport (TCP or Serial) and its parameter can be configured as follow:

{protocol type}:{transport}://{endpoint:{port}|device}?{options}

E.g.

modbus-tcp:tcp://192.168.1.112:2000?unit_id=2&tcp.keep-alive=false

Modbus protocol types

Supported Modbus protocol types in LiveRig Collector are:

  1. RTU (Remote Terminal Unit): is the most common used

  2. Modbus ASCII: Same as RTU but using ASCII characters to transport data using more space size

  3. Modbus over TCP/IP: Uses TCP/IP to communicate through Ethernet

Some examples are demonstrated below:

RTU using Serial

modbus-rtu:serial://dev/ttyUSB0?unit_id=2&serial.baud-rate=9600&serial.parity=EVEN_PARITY

sources.xml

<sources>
    <source>
        <name>Modbus Serial Example 1</name>
        <enabled>true</enabled>
        <mode>client</mode>
        <rig_name>modbus</rig_name>
        <service_company>Your Company</service_company>
        <protocol_name>modbus</protocol_name>
        <protocol_version>1.1b3</protocol_version>
        <endpoint>modbus-rtu:serial://dev/ttyUSB0?unit_id=2&amp;serial.baud-rate=9600&amp;serial.parity=EVEN_PARITY</endpoint>
        ...
    </source>
    ...
</sources>

RTU using TCP

modbus-rtu:tcp://192.168.1.100:502?unit-identifier=5&request-timeout=6000

sources.xml

<sources>
    <source>
        <name>Modbus Serial Example 2</name>
        <enabled>true</enabled>
        <mode>client</mode>
        <rig_name>modbus</rig_name>
        <service_company>Your Company</service_company>
        <protocol_name>modbus</protocol_name>
        <protocol_version>1.1b3</protocol_version>
        <endpoint>modbus-rtu:tcp://192.168.1.100:502?unit-identifier=5&amp;request-timeout=6000</endpoint>
        ...
    </source>
    ...
</sources>

LiveRig Collector works as Master mode to collect Slave data. Slave must be identified by unit-identifier in range from 1 to 247.

Modbus transport types

LiveRig Collector supports different kind of transport connection. Since 5.0.0, both tcp and serial transport modes are supported.

Examples of TCP transport modes:

modbus-tcp:tcp://192.168.1.115:3000?unit-identifier=10
modbus-ascii:tcp://192.168.1.115?unit-identifier=10
modbus-rtu:tcp://192.168.1.115?unit-identifier=10

Examples of SERIAL transport modes:

modbus-ascii:serial://dev/ttyUSB1?unit-identifier=10
modbus-rtu:serial://dev/ttyACM0?unit-identifier=10

Serial modes in different OS examples:

  • For Linux Systems: modbus-rtu:serial:/dev/ttyUSB0

  • For Windows Systems: modbus-rtu:serial:COM1

Some UNIX system is required permission to access serial connection with devices. This can be done by adding the user to the dialout group using a sudo usermod -a -G dialout $USER command.

Modbus options types

The connection string options are used to setup some extra configuration in Modbus protocol. See tables below:

General option table (used both Serial and TCP transports)

Name
Type
Description
Required
Default value

unit-identifier

Integer

Slave device identifier

No

1

request-timeout

Integer

Default timeout for all requests in milliseconds

No

5000 ms

ping-address

String

Simple address, that Liverig will use to check connection to device is active

No

4x00001:BOOL

TCP options table

Name
Type
Description
Required
Default value

port

Integer

Modbus TCP port

No

502

tcp.keep-alive

Boolean

Packets to be sent keeping alive?

No

false

tcp.no-delay

Boolean

Packets should be sent instantly or should give the OS time to aggregate data?

No

true

SERIAL options table

Name
Type
Description
Required
Default value

serial.baud-rate

Integer

Baud rate in bps of the serial port. Available values are: 9600, 14400, 19200, 38400, 57600, 115200, 128000

No

57600

serial.num-data-bits

Integer

Number of bits to send data. Common values: 7 or 8

No

8

serial.num-stop-bits

Integer

Number of stop bit to terminate data transport. Typical value are 1 or 2. NOTE: 1.5 stop bit is not supported

No

1

serial.parity

String

Data parity check. Available values are: NO_PARITY, ODD_PARITY, EVEN_PARITY, MARK_PARITY and SPACE_PARITY

No

NO_PARITY

Collecting data in Modbus

LiveRig Collector works as Master in Modbus to collect data thus sources.xml and modbus.json must be configured to collect typed values.

Parameters in sources.xml

Name
Description
Is required?
Default value

revisionWaitingTime

Timeout, in milliseconds, after which a request is terminated.

No

Infinity

object

Name that will be fetched in modbus.json

Yes

query_period

Interval, in seconds, for the execution of each request

Yes

uid_log

A number, between 1 and 247, that identifies the target PLC

No

1

Example

The configuration below opens a new connection on port 1552

sources.xml

<source>
    <name>Modbus TCP</name>
    <enabled>true</enabled>
    <mode>client</mode>
    <rig_name>NS03</rig_name>
    <service_company>intelie</service_company>
    <protocol_name>modbus</protocol_name>
    <protocol_version>1.1b3</protocol_version>
    <endpoint>modbus://127.0.0.1:1552</endpoint>
    <requests>
        <request>
            <revisionWaitingTime>3000</revisionWaitingTime>
            <object>pump-pressure-1</object>
            <query_period>25</query_period>
            <uid_log>1</uid_log>
        </request>
        <request>
            <revisionWaitingTime>3000</revisionWaitingTime>
            <object>water-flow-1</object>
            <query_period>10</query_period>
            <uid_log>2</uid_log>
        </request>
    </requests>
</source>

modbus.json

{
  "version": "2.0",
  "controllers": {
    "pump-pressure-1": [
      {
        "type": "input-register",
        "start_address": 2,
        "dataType": "float",
        "count": 3,
        "unit": "psi",
        "alias": ["rotary_pump_pressure", "rotation_max_pressure", "hold_back_pressure"]
      },
      {
        "type": "discrete-input",
        "start_address": 4,
        "dataType": "float",
        "count": 2,
        "alias": ["water_pressure"]
      },
      {
        "type": "coil",
        "start_address": 10
      }
    ],
    "water-flow-1": [
      {
        "type": "holding-register",
        "start_address": 2,
        "dataType": "float",
        "unit": "m3"
      },
      {
        "type": "coil",
        "start_address": 3
      }
    ]
  }
}

Compatibility for LiveRig Collector prior to 5.x

Modbus support for LiveRig Collector prior to 5.0.0 is limited to TCP transport only.

The connection string was slightly different as demonstrated below:

modbus://your-ip-address:{port}?{options}

E.g.:

modbus://192.168.1.115:502?unit-identifier=10
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