When monitoring the health of a component, it’s not only important to get an accurate measurement of the parameters in question but also to be able to deliver these measurements in a timely manner. This is where latency comes in.
In this context, latency is the time it takes for a data packet to be transmitted from one node to another within a wireless network. Another use case where latency becomes very important is when different sensor measurements on different devices need to be synchronized.
Latency is usually measured in milliseconds, and, in wireless networks, it is usually not a fixed value. Rather, it depends on the configuration and the choice of different parameters for the network.
Achieving a low latency usually comes with a sacrifice in power consumption, so the choice of parameters that affect latency should be chosen carefully to strike a balance between an acceptable latency while still achieving low power consumption – this is especially true for battery-operated devices.
Keep in mind that latency is also greatly affected by the packet size being transmitted, so reducing the packet size will lead to lower latency values.
Range is defined as the maximum distance between a transmitter and receiver at which reliable communication is still achievable with minimal packet loss. Range is very important for condition monitoring applications that span large spaces such as in a manufacturing plant.
The maximum range of a wireless network mainly depends on the following factors:
- Transmit power
- Receiver sensitivity
- The environment surrounding the network (such as humidity, human bodies, fixed obstacles, and noise from other RF signals operating in the same spectrum)
- The number and spacing of nodes in a mesh network
Keep in mind that there are often regulations and rules restricting the transmit power output of a device, depending on the region and country of operation. Specifications of low-power wireless technologies also typically restrict the maximum transmit power to limit power consumption.
In most condition monitoring applications, the implementor does not have the luxury of replacing the existence machinery with new equipment that has the wireless sensors built in. Rather, more commonly, the task involves retrofitting the equipment with after-market wireless sensor devices to measure the key parameters.
Due to challenges with installation and mounting the sensor devices to the components, these devices will typically be battery powered. So, power consumption is a key parameter that needs to be carefully considered.
There are many factors that affect power consumption, some of which include:
- Frequency of data transmission (radio-on time)
- Amount of data transmission (how long the radio is active)
- Transmit power
- The surrounding environment, and its effect on data retransmissions
- Configuration of certain network parameters
Low-power wireless technologies typically target low duty cycle data applications since the radio is usually the highest power-consuming component of the chipset (the longer the radio is on, the higher the power consumption of the device).
Comparison of Wireless Technologies Suitable for Condition Monitoring
So, based on the attributes we mentioned before: reliability, latency, range, and power consumption, which of the wireless technologies make the most sense for the application of condition monitoring?
These are the most suitable wireless technologies for condition monitoring:
- Bluetooth® Low Energy
- IEEE 802.15.4-based technologies (Thread, Zigbee)
- LPWAN technologies (cellular and non-cellular based): LoRaWAN, LTE-M, NB-IoT
Other worthy mentions include WirelessHART and ISA 100.11a, which are both partially based on the IEEE 802.15.4 standard.
WirelessHART is a wireless protocol that was developed with the goal of being a multi-vendor and interoperable standard. It was designed specifically for the industrial field and supports a time-synchronized, self-healing mesh architecture. ISA 100.11a was also developed with a focus on the automation and control environment and supports mesh topology as well.
Now, let’s compare the most common technologies in terms of the key attributes we listed:
It’s important to note that even within the application of condition monitoring, there are various use cases where one technology may be more appropriate than another for that specific use case.
For example, for applications that require high-bandwidth and large data transfers, Wi-Fi makes the most sense out of the listed technologies. LTE-M is also suitable for these applications, whereas the rest of the technologies will probably not satisfy the need.
If the application involves low-bandwidth and long-range deployments, such as outdoors and in rural areas, then LPWAN technologies make the most sense.
Finally, outside of these somewhat less common use cases within condition monitoring, Bluetooth® Low Energy provides the highest flexibility and a good mix of power consumption, latency, reliability, and range performance to satisfy the most needs.