Cellular connectivity has become a major part of Industrial Networks and is being used considerably more for remote access, predictive maintenance, and monitoring of assets. Setting up a cellular device can be tricky as there are many variables that can affect the reliability and speed of a cellular connection. Before installing a device, some questions need to be asked so that we maximise the availability of our network.
The environment plays a significant role in a cellular installation including, water, glass, hills and mountains, which all affect the behaviour of a signal. A signal may reflect or bounce off an object causing the signal to take a different path to the receiver than the original, arriving out of sync, and potentially causing data loss. As a signal travels through a wall, it will absorb some of that signal causing it to weaken, so this must be considered when installing a device indoors. Another major factor is EMI (Electro-magnetic interference), which the antennas view as noise.
Noise can have a significant effect on a signal to the point of being completely unusable. How to mitigate issues & increase reliability Most of these issues are unavoidable but there are ways to help mitigate their effect so they will have less of an impact on performance and signal quality. A lot of these can be solved with the selection and installation of the antenna. Using a higher gain antenna is one way to increase the performance as this will alleviate some loss from EMI, or any other factor. The higher gain the antenna has, the higher the link budget will be and the more factors it can mitigate. Increasing an antenna’s gain simply focuses the radiated RF into narrower patterns such that there appears to be more power coming from the antenna. Most traditional antennas are omnidirectional which means they radiate RF in multiple directions in a 360-degree plane. In most cases, omnidirectional antennas will meet your installation needs, however, there will be times when a directional antenna may be required. For example, if there is more than one cellular tower within a small geographic area.
Using an omnidirectional antenna, it is going to receive a signal from both towers. This can be problematic if the cellular module keeps switching between the two as the signal fluctuates over time. In this case, using a directional antenna that can focus the RF by pointing towards one specific tower will receive that tower’s signal while ignoring the second tower’s signal. There are some caveats to consider when choosing this path. Using a directional antenna will mean, if that tower should have problems or become congested with users, the overall received signal will decrease significantly causing the cellular module to possibly disconnect from that tower altogether. With the omnidirectional, the cellular module would scan for a stronger signal and connect to the other cellular tower. Another way to increase performance, is by adding height to the antenna, which can significantly improve the received signal when coupled with a low loss coax cable. Many times, it can come down to simple trial and error.
There might be areas on a plant floor that are better suited for receiving signal than others. Sometimes simply moving the antenna to a different location or the device itself can be the difference between a weak or strong signal. Lightning and surge protection If there is one thing that is unpredictable, it is Mother Nature. Lightning storms can spring up at any time and could cause irreparable damage to a cell router if struck by lightning, especially when installed outdoors or if there is an antenna connected on a roof or side of a building. If the cell router installation is in an area where lightning storms are prevalent, it might be wise to consider installing a lightning arrestor. There are different types you can choose from, depending on your preference. One such arrestor is the gas tube suppressors like Novaris’ RF protectors, that connect between the antenna and the cellular router. The gas inside the arrestor acts as a conductor when a surge occurs by ionizing the gas inside it. The gas then passes the voltage through the ground line until things normalise. After a lightning strike occurs, you will need to replace the gas tube, as it will offer no further protection.
Final thoughts Cellular can be a fast and reliable medium for accessing devices and retrieving data if used properly. Too often, users expect the reliability of a wired medium from cellular when that is simply not a feasible expectation. Cellular is a shared medium, which means every device, from mobile phones to M2M devices to tablets, and a single tower can only handle so many concurrent users and they are all competing for access to the network while sharing bandwidth. Cellular is an extremely useful part of an industrial network and as long as you understand where you are installing your device and what issues you may face, it is relatively simple to mitigate those issues.