Tunnel – Regular reading and delivery of Modbus records of a PLC + IP gateway for remote update of the PLC firmware to a webserver

Scenario details:

• We have a PLC Modbus RTU. This PLC has a series of variables/records (for example, a temperature value and 3 meters, etc.) in its internal memory, which must be periodically read and sent to a Web server
• In order to read said records, the MTX-Tunnel must periodically poll the PLC, every 15 minutes, via an RS485serial port. The records to be read are: for temperature, record nº20, and for meters the records in 21, 22 y 23 respectively
• The MTX-Tunnel must send the records value to a web server via HTTP GET using a JSON object after every reading, but must be able, in case of a 2G/3G/4G communications failure, to store up to 1500 records in its flash memory that will be sent once communications are restored
• The PLC has a serial port RS232 that is used to update the firmware. Access to the PLC programming port must be possible at any given time. For this, the RS232 port of the MTX-4GJAVA-IOT-STD-N modem will be used

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

EXAMPLE of settings (file config.txt) for such scenario:

Details:

• The summary of this example is as follows. The modem periodically reads, every 15 minutes, a series of PLC ModBus records and sends them to a web server (to the URL specified in the LOGGER_server parameter) via a JSON object. In cases where a record cannot be sent (because at that moment there is no GPRS coverage or because the server is down) it stores the records in the memory to send them later. Using Telnet it is possible to directly connect to the device and check/change the PLC records in real time (to do so please read the AT^MTXTunnel=getmodbus and AT^MTXTUNNEL=setmodbus commands laid out in this manual)
• The JSON object sent to the URL specified en LOGGER_server is codified as follows:

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

That is, the web server receives a JSON object with the modem’s IMEI (IMEI), a password field (P) that can also be used to identify the device (if you do not want to use the IMEI), the modbus address (A), the time stamp (TS) of when the modbus data has been read, the initial address of the read variables (ST) and V1,V2, … with each of the read variables.

• For the GPRS-Series gateway of the PLC firmware updater we have chosen to work in Server mode (MTX_mode: server) so it is very simple to remotely connect to the MTX-Tunnel via the usual PLC firmware updater, simply stating the IP address and MTX-Tunnel port (if the IP is not fixed, it can be obtained through a missed call, an SMS or even using DynDNS among other options). If your PLC firmware updater does not allow you to enter an IP address, but only a COM port, you can use a virtual COM port such as the one shown in Annex 9
• At the end of the manual you will find how to configure the internal microswitch to activate the RS485 bus of this modem model