PLC4X Apache NiFi Integration

Common properties

The following properties applies to all Plc4x Processors:

• Connection String: A constant connection string such as s7://10.105.143.7:102?remote-rack=0&remote-slot=1&controller-type=S7_1200 or a valid Expression Language (Expression Language NiFi documentation) such as ${plc4x.connection_string}.
• Timeout (miliseconds): Specifies the time in milliseconds for the connection to return a timeout. Is used to renew connections. Can be set with Expression Language.
• Timestamp field name: It defines the name of the field that represents the time when the response from the Plc was received. It will be added to the attributes or to the record deppending on the processor used.
• Address Access Strategy: defines how the processor obtains the PLC addresses. It can take 2 values:

  • Properties as Addreses: For each variable, add a new property to the processor where the property name matches the variable name, and the variable value corresponds to the address tag.

    An example of these properties for reading values from a S7-1200:

    • var1: %DB1:DBX0.0:BOOL
    • var2: %DB1:DBX0.1:BOOL
    • var3: %DB1:DBB01:BYTE
    • var4: %DB1:DBW02:WORD
    • var5: %DB1:DBW04:INT

  • Address Text: Property Address Text must be supplied in JSON format that contains variable name and address tag. Expression Language is supported.

    Using the same example as before:

    • Address Text:

    {
      "var1" : "%DB1:DBX0.0:BOOL",
      "var2" : "%DB1:DBX0.1:BOOL",
      "var3" : "%DB1:DBB01:BYTE",
      "var4" : "%DB1:DBW02:WORD",
      "var5" : "%DB1:DBW04:INT" 
    }
    

    If this JSON is in an attribute plc4x.addresses it can be accessed with Address Text=${plc4x.addresses}.

  • Address File: Property Address File must be supplied with a path to a file in JSON format that contains variable name and address tag. Expression Language is supported.

    For example a file in:

    • Address File:/home/nifi/s7addresses.json
      With the following content

    {
      "var1" : "%DB1:DBX0.0:BOOL",
      "var2" : "%DB1:DBX0.1:BOOL"
    }
    

    If the file name is in an attribute plc4x.addresses_file it can be accessed with Address File=${plc4x.addresses_file}.

When reading from a PLC the response is used to create a mapping between Plc types into Avro. The mapping is done as follows:

Table of data mapping between plc data and Avro types (as specified in Avro specification).

Also, it is important to keep in mind the Processor Scheduling Configuration. Using the parameter Run Schedule (for example to 1 sec), the reading frequency can be set. Note that by default, this value is defined to 0 sec (as fast as possible).

Plc4xSinkRecordProcessor

This processor is record oriented, reads from a formated input flowfile content using a Record Reader (for further information see NiFi Documentation).

The Plc4xSinkRecord Processor can be configured using the common properties defined above and the following property:

• Record Reader: Specifies the Controller Service to use for reading input variables from a flowfile. The Record Reader may use Inherit Schema to emulate the inferred schema behavior.

For the Record Reader property, any reader included in NiFi could be used, such as JSON, CSV, etc (also custom readers can be created).

Plc4xSourceRecordProcessor

This processor is record oriented, formatting output flowfile content using a Record Writer (for further information see NiFi Documentation).

The Plc4xSourceRecord Processor can be configured using the common properties defined above and the following properties:

• Record Writer: Specifies the Controller Service to use for writing results to a FlowFile. The Record Writer may use Inherit Schema to emulate the inferred schema behavior.

Plc4xListenRecordProcessor

This processor is record oriented, formatting output flowfile content using a Record Writer (for further information see NiFi Documentation).

The Plc4xListenRecordProcessor can be configured using the common properties defined above and the following properties:

• Subscription Type: sets the subscription type. It can be “Change”, “Event” or “Cyclic”. The subscritpion types available for each driver are stated in the documentation.
• Cyclic polling interval: In case of “Cyclic” subscription type a time interval must be provided. Must be smaller than the subscription timeout.

Example

An example for reading values from a S7-1200:

• PLC connection String: s7://10.105.143.7:102?remote-rack=0&remote-slot=1&controller-type=S7_1200
• Record Writer: PLC4x Embedded - AvroRecordSetWriter
• Read timeout (miliseconds): 10000
• Timestamp field name: timestamp
• var1: %DB1:DBX0.0:BOOL
• var2: %DB1:DBX0.1:BOOL
• var3: %DB1:DBB01:BYTE
• var4: %DB1:DBW02:WORD
• var5: %DB1:DBW04:INT

Reading values using OPCUA:

• PLC connection String: opcua:tcp://10.105.143.6:4840?discovery=false
• Record Writer: PLC4x Embedded - AvroRecordSetWriter
• Read timeout (miliseconds): 10000
• AcyclicReceiveBit00: ns=2;i=11
• MaxCurrentI_max: ns=2;i=33

For the Record Writer property, any writer included in NiFi could be used, such as JSON, CSV, etc (also custom writers can be created). In this example, an Avro Writer is supplied, configured as follows:

• Schema Write Strategy: Embed Avro Schema
• Schema Cache: No value set
• Schema Protocol Version: 1
• Schema Access Strategy: Inherit Record Schema
• Schema Registry: No value set
• Schema Name: ${schema.name}
• Schema Version: No value set
• Schema Branch: No value set
• Schema Text: ${avro.schema}
• Compression Format: NONE
• Cache Size: 1000
• Encoder Pool Size: 32

The output flowfile will contain the PLC read values. This information is included in the flowfile content, following the Record Oriented presentation using a schema and the configuration specified in the Record Writer (format, schema inclusion, etc). In the schema, one tag will be included for each of the variables defined taking into account the specified datatype. Also, a ts (timestamp) field is additionally included containing the read date. An example of the content of a flowfile for the previously defined properties:

[ {
  "var1" : true,
  "var2" : false,
  "var3" : "\u0005",
  "var5" : 1992,
  "var4" : "4",
  "timestamp" : 1628783058433
} ]