First, DTU cannot connect to the center?

1. First determine whether the setting of the center DEMO is normal (you can use an analog DTU to connect to the center), and then check whether the DTU configuration is correct,  whether the center address and port are set correctly.

2. Whether the DTU signal is normal (check by AT instruction), and whether the SIM card is in arrears.

Second, when the settings of the DTU and the center DEMO are normal, the DTU still cannot connect to the center?

We determine whether the PC running the DEMO is port-mapped  ly (if running on a DMZ server, port mapping is not required); then, make sure that the mapped port is not occupied or blocked by a firewall.

Third, the communication between the central DEMO and the DTU is normal, but can’t connect to the slave PLC ?

1. Whether the parameters of the DTU correspond to the slave PLC, such as baud rate, parity, data bits, s bits;

2. The communication protocol of the PLC is correct (you can communicate with the PC );

3. The DTU does not match the serial port 485 resistance of the slave PLC (the matching resistance is generally between 10 ohms and 200 ohms);

4. Is the DTU and PLC communication interface connected correctly? as the picture shows:

Fourth, the central DEMO and DTU communicate normally, but often drop?

1. Whether the heartbeat packet time of the DTU is set correctly. The length of the heartbeat packet time is related to the local network. Generally, it is set within the time allowed by the local network without data transmission.

2. Is the ID number of the DTU and the SIM card number set to unique? If it is repeated, there will be constant disconnection and reconnection.

Fifth, the reason why can't I establish communication with DTU by using my own RS232 cable?

This is because the connection method of the serial cable is not correct. It is to use Bewis's standard serial cable. We use a 2-pin and 3-pin cross, a 5-pin direct connection, and no flow control.

Note that the longest length of the serial cable between the two female heads should be based on the RS232 standard and cannot exceed 15 meters. The recommendation is to be shorter for normal data communication.