Tunnel – PLC Modbus RTU periodically registers readings, sends them as a JSON object to webserver

Scenario details:

• There is a Modbus RTU PLC. This PLC records some variables such as temperature, pulses, etc. in their register memory table from external devices connected to it. We need to read them and send them to a WebServer
• MTXTunnel will connect every 15 minutes to the PLC serial port. The number for storing temperature is number 20. Pulse counters are stored in registers table number 21, 22 and 23
  respectively
• MTXTunnel will get all data values and convert them to JSON objects in order to send them to a WebServer using HTTP GET procedure. In case the 2G/3G/4G network or server fails, it needs to store up to 1500 readings in MTX-Tunnel’s non volatile internal memory and then it can retry communicating later on
• You also need to be able to access the PLC at any time in order to read the register values in real time or write/change any of PLC’s configuration parameters

Solution: MTX-Tunnel firmware + MTX-Java-IoT/MTX-Java-T/MTX-Java-T2

Config.txt configuration file:

Configuration

Observations

COMM2_baudrate: 9600 COMM2_bitsperchar: 8 COMM2_autorts: off COMM2_autocts: off COMM2_stopbits: 1 COMM2_parity: none GPRS_apn: movistar.es GPRS_login: MOVISTAR GPRS_password: MOVISTAR GPRS_timeout: 0 MTX_PIN: 0000 MTX_mode: none MTX_model: MTX-4G-JAVA-IOT-STD-N MTX_portAux: modbusmaster MTX_TPProtocol: ntp MTX_TPServer: ntp.roa.es MTX_TPServer2: es.pool.ntp.org MTX_ping: 35 MTX_pingIP: 8.8.8.8MODBUS_period: 900 MTX_rssiLevel: 10 SMS_allPhones: on SMS_sendIP: on SMS_ATEnabled: on SMS_ATResponse: on FIREWALL_enabled: off TELNET_enabled: on TELNET_login: user TELNET_password: 1234 TELNET_firewall: off LOGGER_enabled: on LOGGER_password: ID00001 LOGGER_server: www.miservidorWeb.com/json.asp?data= LOGGER_registerSize: 300 LOGGER_numRegistersFlash: 1500 LOGGER_httpMode: getjson MODBUS_address: 1 MODBUS_start: 20 MODBUS_numwords: 4 MODBUS_readCommand: 3 MODBUS_period: 900

Serial port baud rate Number of bits No flow control No flow control 1 stop bit No parity APN GPRS from your network operator GPRS Login GPRS Password Modem is always GPRS connected SIM Card PIN MTX-Tunnel mode MTX modem model AUXILIAR COM port used as master modbus Time synch. protocol Time server Backup time server Ping every 35 minutes without comms IP address to ping Coverage LED activated All phone numbers are authorized IP sent to phone which called or “on” SM Remote AT commands by SMS enabled Modem response to AT command with SMS Any IP will be able to connect to the modem Telnet is activated Telnet login Telnet password Telnet port 20023 We enable the MTX Logger, to store the records Password field can be used as ID device Server URL, will receive JSON data Register size Maximum number of records in MTX HTTP GET (JSON) mode ModBus equipment address ModBus register address to be read Number of registers read Reading command Timing -seconds- read is repeated

Details:

• MTX-4G-JAVA-IOT-STD-N modem is used if the PLC port is the RS485 type, but MTX-4G-JAVA-IOTSTD-N-RS232 terminals are more suitable if PLC has the RS232 port
• Procedure:
  • Every 15 minutes the modem reads a series of PLC ModBus records. They are translated to JSON objects and sent to a WebServer. WebServer URL is configured in LOGGER_server parameter.
  • In the event of there being no coverage in GPRS link or the server is down, MTX-Tunnel stores data in the internal FLASH memory.
  • Using TELNET, it is possible to remotely access the system and read or write any PLC records, readings or configuration parameters. Use the AT^MTXTunnel=getmodbus and AT^MTXTUNNEL=setmodbus commands.
  • The JSON object data sent to the server has following syntax:

{“IMEI”:353234028103206,”P”:”ID00001”,”TYPE”:”MODB”,”A”:1,”TS”:”20/08/12 08:31:44”,”V1”:23,”V2”:275,”V3”:274,”V4”:32765}

IMEI	Modem’s IMEI identifier
P	Password user definable field
TYPE	data type
A	ModBus address
TS	Timestamp
Vx	Variables read

NOTE: You can also develop an easy modbusTCP/modbusRTU gateway as explained in example “Modbus TCP/Modbus RTU GPRS gateway“