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How to Keep Cellular Devices Online for the Industrial Internet of Things

With the Industrial Internet of Things (IoT) such a hot topic these days, the need to keep all of those “things” continuously connected to the Internet has put a premium on networking products that can deliver continuous connectivity without human intervention.

Wireless is the connectivity option of choice for enabling Industrial IoT applications, with cellular communication the most frequently used wireless technology. In fact, more and more manufacturers are adding cellular modems into their Industrial IoT devices, with industrial controllers a prime example. End users now have the option of using cellular controllers for data acquisition and control applications, instead of installing fiber cabling, since using the cellular option can reduce wiring costs by a significant amount, especially when installing controllers at remote, unmanned sites.

In spite of all of the positive benefits that cellular has to offer, if the cellular connection goes down and the device is unable to reconnect, someone will need to go to the remote site to reboot the modem. Cellular connections will definitely experience periods of instability, but if a remote device cannot get reconnected on its own, maintenance engineers may need to spend hours or days going to the field site to reboot or replace the device, resulting a in huge maintenance bill.

Conventional Cellular Reconnection Methods

A solution used by some system integrators to ensure that remote cellular modems get reconnected is to install a relay that automatically cuts off the power supply to the controller when the cellular signal disappears, and then turns the power back on to force the device to reboot. One of the drawbacks of this method is that the relay needs to be controlled by another controller, and that controller needs to check the status of the cellular controller regularly. Another problem with this method is that since the main controller is turned off for several seconds or minutes, I/O data and control signals cannot be transmitted during the reboot period.

A solution used by some controller manufacturers is to provide APIs, watchdogs, or function blocks that engineers can use to program the controller to trigger a reboot process when cellular communication is disconnected. But it is difficult to define exactly when the cellular connection cannot be recovered without rebooting, and consequently engineers may program the device to reboot anyway when the cellular connection is lost. However, in this case, I/O data and control signals cannot be transmitted during the reboot period.

Smart Cellular Reconnection Method

After careful analysis, Moxa’s engineers realized that most cellular disconnection issues can be recovered by (1) simply trying to reconnect to the cellular network, (2) rebooting the cellular modem, or (3) rebooting the system software. In other words, you don’t need to restart the hardware every time the cellular signal gets disconnected. Moxa’s cellular controller puts this knowledge into practice with a smart cellular reconnection mechanism. Users do not need to program the controllers by themselves to trigger a connection retry, a cellular modem reboot, or to initiate a software reboot. When a disconnection occurs, the controller will first try to reconnect to the cellular data network. If the retry fails, the system will reboot the cellular modem and try the reconnection again. If the retry succeeds, the system will start pinging a predefined URL address. If the ping fails, the system will reboot the cellular modem again and continue trying the reconnection and ping cycles. If the reconnection and ping cycle fails four times, the system will reboot the software and then retry the reconnection and ping cycles. If at this point it still isn’t possible to connect to the cellular network, the system will reboot itself and then restart the process from the beginning.

Enabling this function is easy through Moxa’s friendly IOxpress or ioAdmin utilities, as shown in the following screenshot.

With this smart cellular reconnection mechanism, Moxa’s end users do not need to worry about device, data, or control loss at remote sites. Moxa’s cellular controllers all support this smart cellular reconnection mechanism. You can get a free sample unit of a brand new Moxa 4-in-1 wireless ioLogik data acquisition device for your qualified application through Moxa's evaluation program here.

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ioLogik W5300 Series ioAdmin
ioLogik 2500 Series IOxpress
ioLogik 1300 Series IOxpress
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