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Modbus TCP collector

The purpose of this article is to be a reference for Modbus collector part
of the full Data Collection Module documentation

Prerequisite:

A Starter package (SiteManager + accounts) 
A Modbus slave capable device
Other sections in DCM:



The Collectors (array of objects, mandatory ) list elements contains the following fields:
FunctionTypeImportanceDescription
CollectorNamestringmandatoryUnique name (within this confguration file) of a device to collect data from. (This is the name used in the agent configuration). Follows the normal rules for names.
CollectorDesriptionstringoptionalDescription of this collector. For your use, no system function)
CollectorIPAddrstringoptionalDefault IP address (or DNS name) for the device to be polled. The agent Target IP address will take precedence over this.
CollectorPortnointeger > 0 and < 65535optionalDefault port number for the device to be polled. The agent Target Port number will take precedence over this. If neither CollectorPortno , nor agent Target Port Number is specified, the appropriate port will be used, depending on the Protocol parameter value.
Aliasstring optionalThis is the CollectorName of another collector, from which, all the parameters (expect CollectorName , CollectorDescription , CollectorIPAddr and CollectorPortno ) are copied from. An alias cannot refer to another alias.
Protocolstring-enum mandatoryThe protocol used to collected data. Currently 3 possible values exists: "OPC-UA/TCP", "Modbus/TCP", "Http/GET" and "Simulator".
ConnectRetryMininteger > 0 mandatoryMinimum number of seconds before trying to reestablish a connection to the device being sampled. An exponential backoff algorithm is used to retry connection establishment, starting after ConnectRetryMin and increasing to ConnectRetryMax.
ConnectRetryMaxinteger > 0mandatoryMaxumin number of seconds before trying to reestablish a connection to the device being sampled.
ModbusAccessObjectoptionalcollection of parameters needed to access a given Modbus server.
SamplePointsArray of objectsmandatoryList of samples to be collected, possibly aggregated and stored in the Store'n'Forward database.

Example of OPCUAaccess object
{
"CollectorName": "ModbusGOT",
"CollectorDescription": "My first modbus",
"Protocol": "ModBus/TCP",
"ConnectRetryMin": 2,
"ConnectRetryMax": 240,
"ModbusAccess": {

ModbusAccess

The ModbusAccess objects contains the following elements:
FunctionTypeImportanceDescription
ModbusFCsArray of objectsmandatoryList of modbus functioncode (FCs) to be performed during collection of data if the Protocol is "Modbus/TCP".
ModbusTimeoutinteger > 0optionalTimeout (in millisecs) for all modbus FC requests. If not present, the value 500 is used.
ModbusRegswapbooleanoptionalIf true, the 16bit register values retrieved will be byteswapped before being used. If not specified the value is false.
0x12345678 > 0x34127856


ModbusFCs

The ModbusFCs objects contains the following elements:
FunctionTypeImportanceDescription
ModbusFCIDinteger >= 0mandatoryis a unique ID (within this Collectors element) for this entry. (Used by the SamplePoints entries.
ModbusFCSlaveAddress(integer >= 0 and <= 247 or 255optionalThe Modbus Slave Address for this access. Note that this is only used in Modbus gateway devices (and should be between 0 and 247), whereas true Modbus endpoint devices should use the value 255. If this not present, the value 255 is used.
ModbusFCstring-enummandatoryis the type of Modbus function code used collecting data. Possible values are:
"coils" (FC 1)
"inputs" (FC 2)
"holding-registers" (FC 3)
"input-registers" (FC 4)
ModbusFCStartinteger >= 0mandatoryStart address on the Modbus for this access.
ModbusFCCountinteger >= 0mandatoryNumber of units (bits or registers) to read in one access.
ModbusFCSampleIntervalinteger >= 0mandatoryNumber of seconds between each collection of data using this FC. If the interval is 0, only event-driven polling is used.
ModbusFCTimeoutinteger > 0optionalTimeout (in millisecond) for this Modbus FC requests. If not present, the value is that of ModbusTimeout referenced by the ModbusFCID.
ModbusFCRegswapbooleanoptionalIf true, the 16bit register values retrieved will be byte-swapped before being used. If not specified the value is that of the ModbusRegswap referenced by the ModbusFCID.

Samplepoint items

The SamplePoints objects contains the following elements:
FunctionTypeImportanceDescription
SampleNamestringmandatoryName of this sampled value (sometimes called a tagname). Follows the normal rules for names.
SampleDescriptionstringoptionalis a text description of this sample value.
SampleUnitstringoptionalis a description of the unit of messurement for this sample.
SampleGroupstringoptionaldesignates (in some datasrvs) that all samplepoints in that group should be handled (displayed) together. The DCM system itself places no meaning on this group affiliation.
SamplesSavedinteger > 0mandatoryis the number of values collected that is saved as minimum in the Store'n'Forward database. If set to 0 the Samplepoint isn't stored in the S'n'F database and thus not delivered to cloud, but can be used for aggregations.
OnlySaveOnChangedbooloptionalcontrol if new sample values should only be saved to the store-and-forward database if the values have changed since last sample. If not set, it is false.
SampleDataTypestring-enummandatoryThe type of data collected. The possible values are: "bool" (1 bit), "sbyte" (8 bit signed), "byte" (8 bit unsigned), "int16" (16 bit signed), "uint16" (16 bit unsigned), "int32" (32 signed), "uint32" (32 bit unsigned), "int64" (64 bit signed), "uint64" (64 bit unsigned), "float" (32 bit), "double" (64 bit), "string" (variable text up to 24575 bytes. Includes terminating NUL), "data" (variable variable data up to 24575 bytes).
SampleLowerLimitinteger/doubleoptionalThe lower limit for the collected data. If the collected data value is less than SampleLowerLimit it is evaluated inaccordance to SampleLimitDiscard and SampleLimitAlarm.
SampleUpperLimitinteger/doubleoptionalThe upper limit for the collected data. If the collected data value is more than SampleUpperLimit it is evaluated inaccordance to SampleLimitDiscard and SampleLimitAlarm.
SampleLimitDiscardboolmaybe-optionalControls if a sample limit violation results in the sample value being discarded. Mandatory if either SampleLowerLimit or SampleUpperLimit is present.
SampleLimitAlarmboolmaybe-optionalControls if a sample limit violation generates an alarm. Mandatory if either SampleLowerLimit or SampleUpperLimit is present.
ModbusValueObjectmaybe-optionalDescription of how to extract a collected datavalue from a FC collected value. Mandatory of the protocol type is "Modbus/TCP".

ModbusFCs

The ModbusValue object contains the following elements: FCREF (integer >= 0, mandatory) This is a reference to the ModbusFCs element with the same value of it's field ModbusFCID. FCOffset (integer >= 0, mandatory). This is the addressing offset (relative to the referenced __ModbusFCs__s ModbusStart address. It must be lower than ModbusCount field for that same ModbusFCs element. FCDataMask (integer >= 0, optional) This is the value that is bit-wise AND'ed with the collected value. FCDataShift (integer, optional). This is the number of bits the collected value is shifted right.
FunctionTypeImportanceDescription


Example collecting
64 coils from 27 to 90
53 input registers from 3 to 55
33 holding registers from 100 to 132

{
 "CollectorName": "Test1ModbusDevice",
 "CollectorDescription": "My first modbus",
 "Protocol": "ModBus\/TCP",
 "ConnectRetryMin" : 2,
 "ConnectRetryMax" : 240,
 "ModbusAccess" : {
  "ModbusFCs": [
  {
  "ModbusFCID": 1,
  "ModbusFCSlaveAddress": 1,
  "ModbusFC": "coils",
  "ModbusFCStart": 27,
  "ModbusFCCount": 64,
  "ModbusFCSampleInterval": 5
   },
   {
   "ModbusFCID": 2,
   "ModbusFCSlaveAddress": 1,
   "ModbusFC": "inputs",
   "ModbusFCStart": 3,
   "ModbusFCCount": 53,
   "ModbusFCSampleInterval": 3
   },
   {
   "ModbusFCID": 3,
   "ModbusFCSlaveAddress": 1,
   "ModbusFC": "holding-registers",
   "ModbusFCStart": 100,
   "ModbusFCCount": 33,
   "ModbusFCSampleInterval": 2
   }
  ],
  "ModbusTimeout" : 1000
  },
 "SamplePoints": [
  {
  "SampleName": "test1",
  "SampleDescription": "First coil",
  "SamplesSaved": 10,
  "SampleDataType": "bool",
  "ModbusValue": {
   "FCREF": 1,
   "FCOffset": 0
   },
  "SampleLowerLimit": 0,
  "SampleUpperLimit": 1,
  "SampleLimitDiscard": false,
  "SampleLimitAlarm": false
  },
  {
  "SampleName": "input1",
  "SampleDescription": "first input",
  "SamplesSaved": 10,
  "SampleDataType": "int16",
  "ModbusValue": {
   "FCREF": 2,
   "FCOffset": 0
   },
  "SampleLowerLimit": 0,
  "SampleUpperLimit": 1000,
  "SampleLimitDiscard": false,
  "SampleLimitAlarm": false
  },
  {
  "SampleName": "Holding1",
  "SampleDescription": "first holding register",
  "SamplesSaved": 10,
  "SampleDataType": "int16",
  "ModbusValue": {
   "FCREF": 3,
   "FCOffset": 0
   },
  "SampleLowerLimit": 0,
  "SampleUpperLimit": 1000,
  "SampleLimitDiscard": true,
  "SampleLimitAlarm": true
  }
 ]
}

See complete Modbus examples here:
Creation date: 11/12/2019 14:07 (skr@secomea.com)      Updated: 04/09/2020 13:39 (tvo@secomea.com)