In the field of IIoT, the data transfer unit, Cellular Modem, is widely used in various monitoring, data collection and remote control scenarios as a key device for remote data transmission. Among them, SMS mode, as an important communication method of Cellular Modem, has irreplaceable advantages in specific environments due to its characteristics of no dependence on network coverage, low cost, and high reliability. However, in practical applications, sometimes the Cellular Modem SMS mode does not work, which not only affects the normal transmission of data, but also may pose a threat to the stability and reliability of the entire system.

1. What is the working principle of Cellular Modem SMS mode

Before discussing the reasons for the inoperative SMS mode of the Cellular Modem, we first need to understand the basic working principle of the SMS mode of the Cellular Modem. The SMS mode of Cellular Modem mainly relies on the SMS service of the mobile communication network. It achieves the conversion and transmission between serial data and SMS through the built-in SMS module of the Cellular Modem or external SMS devices such as SMS modems. When the Cellular Modem receives data sent by the serial port, it will encapsulate it into a SMS format and send it to the specified mobile phone number through the mobile communication network; Similarly, when the Cellular Modem receives a short message from the mobile communication network, it will also parse it into serial port data and send it to the connected terminal device.

2. Reasons for the inoperative SMS mode of the Cellular Modem

2.1 Problems with mobile communication networks

● Insufficient signal coverage: If the mobile communication network signal coverage in the area where the Cellular Modem is located is insufficient or the signal quality is poor, it will result in the inability to send or receive SMS messages normally.
● SIM card problem: SIM card arrears, damage or improper installation may cause the SMS service to not work properly.
● Operator restrictions: Some operators may have restrictions or adjustments on SMS services, such as limiting the frequency of SMS sending and the content format of SMS messages.

2.2 Cellular Modem equipment problems

● lSMS module failure: The built-in SMS module of the Cellular Modem or the external SMS modem may fail, resulting in the inability to send or receive SMS messages normally.
● Configuration error: The SMS parameter configuration error of the Cellular Modem, such as the SMS center number and SMS format, may also cause the SMS mode to not work.
● Firmware issue: The firmware version of the Cellular Modem is outdated or has bugs, which may also affect the normal use of the SMS function.

2.3 External factor interference

● lElectromagnetic interference: Strong electromagnetic fields may interfere with the communication module of the Cellular Modem, resulting in failure to send or receive SMS messages.
● Power issues: Unstable power supply or poor power quality may also affect the normal operation of the Cellular Modem.

3. Troubleshooting and solution strategies

3.1 Checking the mobile communication network

● Signal test: Use a signal tester or mobile phone to check the signal strength and quality of the mobile communication network in the area where the Cellular Modem is located.
● SIM card check: confirm whether the SIM card is properly installed, whether it is overdue, whether it is damaged, and try to replace it with a new SIM card for testing.
● Contact the operator: Consult the operator about the restrictions and adjustments of SMS services to ensure that the SMS service of the Cellular Modem is not restricted.

3.2 Checking the Cellular Modem device

● ISMS module check: check whether the built-in SMS module of the Cellular Modem or the external SMS modem is working properly. If necessary, replace it with a new module or device for testing.
● Configuration check: Carefully check the SMS parameter configuration of the Cellular Modem to ensure that all parameters are set correctly.
● Firmware upgrade: Check whether the firmware version of the Cellular Modem is outdated or has bugs. If necessary, perform a firmware upgrade operation.

3.3 Investigate external factors

● Troubleshooting electromagnetic interference: Check whether there is a strong electromagnetic field interference source around the Cellular Modem, and try moving the Cellular Modem to another location for testing.
● Power supply inspection: check whether the power supply of the Cellular Modem is stable and reliable. If necessary, replace it with a new power supply for testing.

The inoperative SMS mode of the Cellular Modem may be caused by various reasons, including problems with the mobile communication network, problems with the Cellular Modem device, and interference from external factors. When troubleshooting and solving such problems, it is necessary to comprehensively consider various possible factors and conduct troubleshooting one by one according to a certain order and steps. Through the troubleshooting and resolution strategies provided in this article, we believe that we can help you quickly locate the cause of the problem and take appropriate measures to restore the normal operation of the Cellular Modem SMS mode.