February 21, 2019 at 12:32Industrial wireless networks: which one to choose?
We are used to the fact that data can be easily transmitted by air. Wireless data transmission is used everywhere - WiFi, Bluetooth, 3G, 4G and others. And the main criterion for evaluating a particular technology has become the speed and data transfer and its volume. But is this always important?
For example, in the industry, wireless technologies are also actively gaining momentum, but in addition to the usual WiFi, Bluetooth and other modern technologies, at industrial sites one can often find, at first glance, exotic protocols. For example, WirelessHART or Trusted Wireless 2.0, transmitting data at a maximum speed of 250 kbps. First you start to think that these are some kind of outdated technologies and you need to switch to WiFi and other “fast” protocols. But is this true for industry? Let's figure it out.
Compare four technologies - WiFi, Bluetooth, Trusted Wireless 2.0 and WirelessHART. We will consider all technologies at a frequency of 2.4 GHz. Other frequencies for the Russian Federation are not very relevant (well, maybe 5 GHz, but this frequency range only supports WiFi).
We will compare by several criteria:
The comparison is theoretical.
The first thing that questions begin to arise when considering networking with wireless technology is the reliability of data transfer. By reliability of data transmission I propose to understand data transmission with a permanent connection and without data loss.
Two main factors can cause data loss and connection failure:
Electromagnetic interference
Electromagnetic interference at an industrial facility is generated, first of all, by frequency converters, electric drives and other primary equipment. Such interference has a frequency range that is a multiple of kHz or MHz. And all the technologies that we took for comparison work at a frequency of 2.4 GHz. Interference from primary equipment simply does not reach this range. Thus, other wireless systems transmitting data at a frequency of 2.4 GHz become a source of interference. There are two completely different approaches for ensuring electromagnetic compatibility of these systems:
When using DSSS, the useful signal passes through the spreading code generator, where one bit of useful information is replaced by N bits, which increases the clock frequency by N times. This affects the expansion of the spectrum also N times. At the receiver, this signal passes through the same generator and information is decoded. The advantage of this approach is the ability to transmit data at a very high speed. The signal occupies a certain frequency band and narrow-band interference distorts only some frequencies of the spectrum, but there is enough information to reliably decode the signal. But after a certain threshold of the spectrum width of the interference frequency, the signal will be impossible to decode. The generator simply does not understand where the useful signal is and where it is superimposed.
Dsss
When using FHSS, the data rate changes in a pseudo-random order. In this case, the resulting interference will affect only one of the random frequencies, regardless of the width of the spectrum.
FHSS
Thus, if serious electromagnetic interference occurs in the FHSS system, some of the data will be lost, and in the DSSS system, the data transfer will stop completely.
WiFi uses DSSS. The width of one channel is 22 MHz and, accordingly, 14 WiFi channels are available in the 2.4 GHz band. Only 13 is available in Russia. At the same time, 3 non-overlapping channels are available for use. Surely, many of you have watched the picture of how WiFi is completely at home. This can happen just because the neighbor has an access point operating on the same channel as your point, or on an overlapping channel.
Bluetooth uses FHSS technology. The width of one channel is 1 MHz. 79 channels are available for rebuilding and access. As with WiFi, a different number of channels may be available in different countries.
Wireless HART uses a combination of FHSS and DSSS. The width of one channel is 2 MHz and all channels are located at a width of 5 MHz, i.e. 16 channels are available and they are all non-overlapping.
Trusted Wireless 2.0 uses FHSS technology. Devices have 127 channels available for tuning. The number of frequencies available for selection by a particular device depends on the “black list of frequencies”, which is configured to ensure compatibility with other wireless systems, and whether special frequency groups (RF bands) are used to optimize the wireless network.
Fig. Signal attenuation due to the propagation of radio waves in free space and the occurrence of reflections
During propagation in the transmission medium, the signal weakens due to various external influences. The main factor is the reflections that occur during the propagation of the radio wave. The signal from the transmitter to the receiver propagates in several directions. In this regard, several waves reach the receiver that contain the same information, but due to different propagation paths, they can have different phases. This can either attenuate the signal (when the incoming radio waves are in antiphase) or amplify (when the phases coincide). Against the background of this problem, FHSS receives an additional advantage - the frequency at which data is transmitted is constantly changing, which automatically solves the physical problem described above. If during the propagation of a radio wave in several directions, data transmission is not possible at the same frequency,
Fig. Signal attenuation due to the propagation of radio waves in free space and the occurrence of reflections
As mentioned above, interference can only be caused by other systems operating at a frequency of 2.4 GHz. Due to the fact that wireless networks in industry are gaining more and more popularity, there are more such systems at sites. Therefore, the issue of ensuring the compatibility of wireless networks is very important for the organization of reliable and uninterrupted data transmission.
Worst of all with WiFi compatibility. Due to the fact that WiFi uses only DSSS as modulation, and the channel has a sufficiently large width, using it simultaneously with other wireless technologies is quite problematic. At the same time, as mentioned above, we can create only three WiFi networks, but this only happens in an ideal world. In reality, much more WiFi networks get along in any apartment building or shopping center, and we get networks that operate on overlapping channels, which significantly degrades the quality of communication, and sometimes it just makes it impossible to connect to WiFi.
In the top of compatibility is Trusted Wireless. This protocol offers a frequency blacklist mechanism in addition to FHSS. This mechanism allows you to put the range of frequencies that are used by other networks in the "black list". The frequencies from this list are not used by Trusted Wireless 2.0 devices, and tuning to these frequencies is not performed.
Wireless HART with compatibility is also doing well - FHSS is also used, and it is possible to use blacklisted channels, but the small number of channels for frequency tuning does not allow it to be as flexible as Bluetooth or Trusted Wireless. In the last two protocols, if there was a hindrance at some frequency, it is possible to switch to many other channels.
Information security is now a very active trend in industrial automation, and this issue cannot be ignored, especially when talking about wireless networks, since information is transmitted through an insecure interface - in fact, through the air. It is important to consider and prevent unauthorized access and transmit data in encrypted form.
Data transmitted over WiFi can be protected using various authentication and encryption methods (WEP, TKIP, WPA, WPA-2), but there are quite a few different information security threats when using WiFi. And due to the popularity of the protocol, all these methods are googled very easily, not to mention multiple video reviews on YouTube. (usually all vulnerabilities are discussed and around the WiFi hacking a large enough community is always built)
The Bluetooth connection is secured with a PIN code and encryption. But Bluetooth is the same as WiFi. This is a very popular open protocol, and there is a lot of information on how to crack it on these Internet sites.
Thanks to proprietary technology, Trusted Wireless 2.0-based wireless channel is much better protected against possible attacks than open protocols.
In addition, Trusted Wireless 2.0 has two security mechanisms: encryption of all transmitted data using the AES-128 protocol and a proprietary authentication protocol that allows you to verify that the message was received by an authorized recipient due to the fact that this message has a special code that cannot to be repeated.
WirelessHART is secured with AES encryption with a 128-bit key.
Technologies that use FHSS also receive an additional bonus, since the transition from frequency to frequency occurs according to a pseudo-random algorithm, which is determined individually for each connection.
For wireless data transmission, especially for outdoor applications, the data transmission range plays a decisive role. But also in applications where there is no need for data transmission over long distances, a high level of receiver sensitivity creates a reserve system for data transmission in difficult conditions, for example, data transmission in the absence of direct visibility.
The sensitivity level is affected by the data rate. Each bit is transmitted with a certain transmit power P. The energy for each bit is determined by the formula Ebit = P * tbit, where tbit is the transmission time of this bit.
With a decrease in the data transfer rate, the transmission time of each bit increases, which gives an increase in energy per bit, due to which we get a significant signal gain.
The following data transfer rates can be selected in Trusted Wireless 2.0:
WiFi, with a data transfer rate of 54 Mbps over a wireless network, allows data to be transmitted over distances of up to 1 km, using a powerful narrow-focus antenna. If you reduce the speed to 6 Mbit / s, then you can achieve a data transmission distance of 1 km to 2 km.
Bluetooth has more modest speeds compared to WiFi (about 1 Mbps), and while data can be transmitted over distances of up to 1.5 km.
WirelessHART operates at a data transfer rate of 250 kbps. The average distance is considered to be 255 m. With a directional antenna, distances of about 2 km can also be achieved, but, as a rule, field sensors or WirelessHART adapters have not very powerful omnidirectional antennas, which give an average distance of 255 m.
The topologies used also have a significant difference.
If we talk about Bluetooth, then you can use two topologies: point-to-point and star. Up to 7 devices can be connected to a star.
WiFi offers a richer selection. Traditionally, you can organize a star topology - we all created it at home repeatedly by connecting several devices to a home access point. But you can also create more complex topologies. Some devices can be used in the “bridge” mode, which allows the device to act as a repeater for WiFi. Also, devices are now available that allow you to create mesh networks (about them a little later) based on WiFi. (e.g. FL WLAN 1100 - 2702534). And WiFi allows you to organize the so-called roaming. A network is called roaming when several access points with the same SSID are installed, and the client can move from one access point to another (proper WiFi coverage must be provided), while remaining in the same wireless network.
Trusted Wireless 2.0 also allows you to use devices as repeaters and, moreover, restore communication in the event of a signal break. Those. if the device loses connection, then it is looking for another nearest repeater through which data can be transmitted. Thus, communication is restored, and data begins to be transmitted through the backup channel. Communication restoration takes from milliseconds to seconds - depending on the selected data transfer rate. A similar topology, where communication channels line up through arbitrarily selected repeaters, is called a mesh topology.
In addition to mesh topology, devices with Trusted Wireless 2.0 support point-to-point, star, line topologies.
Due to the high sensitivity level of Trusted Wireless 2.0 device receivers, sometimes nodes are connected not to the nearest repeaters, but to more remote ones. To avoid such situations, Trusted Wireless 2.0 provides a “black list of repeaters” (English parent-black-listing), which defines the nodes with which the connection should not be established. A “white list of repeaters” (eng. Parent-white-listing) is also provided, which indicates the nodes that are preferred for connection. By default, all repeaters are allowed to connect.
WirelessHART also uses a mesh network to which 254 end sensors can be connected.
Internal data exchange between individual nodes is necessary to maintain the wireless network, regardless of the amount of information transmitted. Thus, the process of adding a new node to the network, as well as the management of existing nodes, plays an important role in terms of ensuring the reliability of the network and optimizing the transmitted traffic.
WirelessHART uses a centralized site management approach. There is a “manager" on the network that sends all requests to nodes and receives responses. Accordingly, this approach creates a large amount of traffic passing through a single network node - the manager.
The same is true for WiFi and Bluetooth. Here, the entire data exchange goes through access points, and if the access point fails, the devices will no longer be able to exchange data.
Trusted Wireless 2.0, in turn, uses a distributed approach. Network management is divided into parent / child zones (parent / child, P / C). The repeater (or the central node of the network) acts as the parent through which other repeaters or end devices, the heirs, are connected to the network. Thus, parents and heirs form a tree structure. The parent is responsible for all direct heirs and is responsible for connecting the new heir. All this information is not sent to the central device, but remains within the parent / heir zone, which significantly reduces network traffic.
For example, if you need to connect a new device to the network, this will happen in several stages:
And all these actions are carried out within the framework of one P / C zone. For comparison, in WirelessHART, using a centralized approach, connecting a new node to the network requires 6-7 commands. For a simple point-to-point network, the join operation will take about 2 seconds, and data exchange will begin in 10 seconds. A network consisting of 100 nodes will require about 600-700 commands for connecting and exchanging data, and it can only start in 25 minutes!
Also, within one P / C zone, the parent device collects diagnostic information from the devices in this zone and stores all this information.
Fig. Parent / child zone partitioning (parent / child - P / C)
Also, this approach significantly reduces network convergence time.
If the network manager is de-energized in a centrally controlled network, then all information about the connections in this network will be lost and the network will be restored for a rather long time.
In a network based on Trusted Wireless 2.0, management processes are performed in parallel in different branches of the tree, which gives significant acceleration during network recovery.
What do we have in total? Trusted Wireless and WirelessHART, although much slower in speed, are not always the most important criteria for industrial networks. Often, wireless technology is needed in order to expand the cable, which is not possible to lay. In such cases, often the task is to transmit discrete and analog signals, and this does not require high speeds. Or you need to collect data from some remote installation that exchanges data via PROFIBUS DP or Modbus RTU - these protocols in most applications are also not demanding for the data transfer speed, but the station itself can be quite far away. WiFi and Bluetooth do not provide long-distance data transfers. And setting up WiFi and Bluetooth at ranges from 1 km is a rather laborious task. Trusted Wireless, on the contrary,
But what is really important for the industry is the reliability of data transfer and its compatibility with existing wireless systems. This is what Trusted Wireless and WirelessHART can boast of - through the use of FHSS and blacklists, they are very reliable and allow for very high compatibility with other technologies.
But this does not mean that WiFi or Bluetooth are not used at industrial facilities. They are also often used, but not much for other tasks. They allow you to organize data transmission at high speed over short distances, for example: automation of a large warehouse or machine room.
Therefore, you cannot give preference to any one technology - each is suitable for its task and most often, they are used together in the framework of a single process control system.
Need help building an industrial network? Visit our website .
For example, in the industry, wireless technologies are also actively gaining momentum, but in addition to the usual WiFi, Bluetooth and other modern technologies, at industrial sites one can often find, at first glance, exotic protocols. For example, WirelessHART or Trusted Wireless 2.0, transmitting data at a maximum speed of 250 kbps. First you start to think that these are some kind of outdated technologies and you need to switch to WiFi and other “fast” protocols. But is this true for industry? Let's figure it out.
Compare four technologies - WiFi, Bluetooth, Trusted Wireless 2.0 and WirelessHART. We will consider all technologies at a frequency of 2.4 GHz. Other frequencies for the Russian Federation are not very relevant (well, maybe 5 GHz, but this frequency range only supports WiFi).
We will compare by several criteria:
- reliability of data transmission;
- compatibility with other wireless networks;
- data transfer security;
- data transmission range;
- network structure;
- the nature of the interaction of network nodes.
The comparison is theoretical.
Data Reliability
The first thing that questions begin to arise when considering networking with wireless technology is the reliability of data transfer. By reliability of data transmission I propose to understand data transmission with a permanent connection and without data loss.
Two main factors can cause data loss and connection failure:
- electromagnetic interference;
- signal attenuation due to the propagation of radio waves in free space and the occurrence of reflections.
Electromagnetic interference
Electromagnetic interference at an industrial facility is generated, first of all, by frequency converters, electric drives and other primary equipment. Such interference has a frequency range that is a multiple of kHz or MHz. And all the technologies that we took for comparison work at a frequency of 2.4 GHz. Interference from primary equipment simply does not reach this range. Thus, other wireless systems transmitting data at a frequency of 2.4 GHz become a source of interference. There are two completely different approaches for ensuring electromagnetic compatibility of these systems:
- the use of broadband modulation with direct spreading of the spectrum (Direct Sequence Spread Spectrum - DSSS);
- the use of pseudo-random tuning of the working frequency (Frequency Hopping Spread Spectrum - FHSS).
When using DSSS, the useful signal passes through the spreading code generator, where one bit of useful information is replaced by N bits, which increases the clock frequency by N times. This affects the expansion of the spectrum also N times. At the receiver, this signal passes through the same generator and information is decoded. The advantage of this approach is the ability to transmit data at a very high speed. The signal occupies a certain frequency band and narrow-band interference distorts only some frequencies of the spectrum, but there is enough information to reliably decode the signal. But after a certain threshold of the spectrum width of the interference frequency, the signal will be impossible to decode. The generator simply does not understand where the useful signal is and where it is superimposed.
Dsss
When using FHSS, the data rate changes in a pseudo-random order. In this case, the resulting interference will affect only one of the random frequencies, regardless of the width of the spectrum.
FHSS
Thus, if serious electromagnetic interference occurs in the FHSS system, some of the data will be lost, and in the DSSS system, the data transfer will stop completely.
WiFi uses DSSS. The width of one channel is 22 MHz and, accordingly, 14 WiFi channels are available in the 2.4 GHz band. Only 13 is available in Russia. At the same time, 3 non-overlapping channels are available for use. Surely, many of you have watched the picture of how WiFi is completely at home. This can happen just because the neighbor has an access point operating on the same channel as your point, or on an overlapping channel.
Bluetooth uses FHSS technology. The width of one channel is 1 MHz. 79 channels are available for rebuilding and access. As with WiFi, a different number of channels may be available in different countries.
Wireless HART uses a combination of FHSS and DSSS. The width of one channel is 2 MHz and all channels are located at a width of 5 MHz, i.e. 16 channels are available and they are all non-overlapping.
Trusted Wireless 2.0 uses FHSS technology. Devices have 127 channels available for tuning. The number of frequencies available for selection by a particular device depends on the “black list of frequencies”, which is configured to ensure compatibility with other wireless systems, and whether special frequency groups (RF bands) are used to optimize the wireless network.
Fig. Signal attenuation due to the propagation of radio waves in free space and the occurrence of reflections
During propagation in the transmission medium, the signal weakens due to various external influences. The main factor is the reflections that occur during the propagation of the radio wave. The signal from the transmitter to the receiver propagates in several directions. In this regard, several waves reach the receiver that contain the same information, but due to different propagation paths, they can have different phases. This can either attenuate the signal (when the incoming radio waves are in antiphase) or amplify (when the phases coincide). Against the background of this problem, FHSS receives an additional advantage - the frequency at which data is transmitted is constantly changing, which automatically solves the physical problem described above. If during the propagation of a radio wave in several directions, data transmission is not possible at the same frequency,
Fig. Signal attenuation due to the propagation of radio waves in free space and the occurrence of reflections
Compatibility with other wireless networks
As mentioned above, interference can only be caused by other systems operating at a frequency of 2.4 GHz. Due to the fact that wireless networks in industry are gaining more and more popularity, there are more such systems at sites. Therefore, the issue of ensuring the compatibility of wireless networks is very important for the organization of reliable and uninterrupted data transmission.
Worst of all with WiFi compatibility. Due to the fact that WiFi uses only DSSS as modulation, and the channel has a sufficiently large width, using it simultaneously with other wireless technologies is quite problematic. At the same time, as mentioned above, we can create only three WiFi networks, but this only happens in an ideal world. In reality, much more WiFi networks get along in any apartment building or shopping center, and we get networks that operate on overlapping channels, which significantly degrades the quality of communication, and sometimes it just makes it impossible to connect to WiFi.
In the top of compatibility is Trusted Wireless. This protocol offers a frequency blacklist mechanism in addition to FHSS. This mechanism allows you to put the range of frequencies that are used by other networks in the "black list". The frequencies from this list are not used by Trusted Wireless 2.0 devices, and tuning to these frequencies is not performed.
Wireless HART with compatibility is also doing well - FHSS is also used, and it is possible to use blacklisted channels, but the small number of channels for frequency tuning does not allow it to be as flexible as Bluetooth or Trusted Wireless. In the last two protocols, if there was a hindrance at some frequency, it is possible to switch to many other channels.
Data Security
Information security is now a very active trend in industrial automation, and this issue cannot be ignored, especially when talking about wireless networks, since information is transmitted through an insecure interface - in fact, through the air. It is important to consider and prevent unauthorized access and transmit data in encrypted form.
Data transmitted over WiFi can be protected using various authentication and encryption methods (WEP, TKIP, WPA, WPA-2), but there are quite a few different information security threats when using WiFi. And due to the popularity of the protocol, all these methods are googled very easily, not to mention multiple video reviews on YouTube. (usually all vulnerabilities are discussed and around the WiFi hacking a large enough community is always built)
The Bluetooth connection is secured with a PIN code and encryption. But Bluetooth is the same as WiFi. This is a very popular open protocol, and there is a lot of information on how to crack it on these Internet sites.
Thanks to proprietary technology, Trusted Wireless 2.0-based wireless channel is much better protected against possible attacks than open protocols.
In addition, Trusted Wireless 2.0 has two security mechanisms: encryption of all transmitted data using the AES-128 protocol and a proprietary authentication protocol that allows you to verify that the message was received by an authorized recipient due to the fact that this message has a special code that cannot to be repeated.
WirelessHART is secured with AES encryption with a 128-bit key.
Technologies that use FHSS also receive an additional bonus, since the transition from frequency to frequency occurs according to a pseudo-random algorithm, which is determined individually for each connection.
Data transmission range
For wireless data transmission, especially for outdoor applications, the data transmission range plays a decisive role. But also in applications where there is no need for data transmission over long distances, a high level of receiver sensitivity creates a reserve system for data transmission in difficult conditions, for example, data transmission in the absence of direct visibility.
The sensitivity level is affected by the data rate. Each bit is transmitted with a certain transmit power P. The energy for each bit is determined by the formula Ebit = P * tbit, where tbit is the transmission time of this bit.
With a decrease in the data transfer rate, the transmission time of each bit increases, which gives an increase in energy per bit, due to which we get a significant signal gain.
The following data transfer rates can be selected in Trusted Wireless 2.0:
WiFi, with a data transfer rate of 54 Mbps over a wireless network, allows data to be transmitted over distances of up to 1 km, using a powerful narrow-focus antenna. If you reduce the speed to 6 Mbit / s, then you can achieve a data transmission distance of 1 km to 2 km.
Bluetooth has more modest speeds compared to WiFi (about 1 Mbps), and while data can be transmitted over distances of up to 1.5 km.
WirelessHART operates at a data transfer rate of 250 kbps. The average distance is considered to be 255 m. With a directional antenna, distances of about 2 km can also be achieved, but, as a rule, field sensors or WirelessHART adapters have not very powerful omnidirectional antennas, which give an average distance of 255 m.
Network structure
The topologies used also have a significant difference.
If we talk about Bluetooth, then you can use two topologies: point-to-point and star. Up to 7 devices can be connected to a star.
WiFi offers a richer selection. Traditionally, you can organize a star topology - we all created it at home repeatedly by connecting several devices to a home access point. But you can also create more complex topologies. Some devices can be used in the “bridge” mode, which allows the device to act as a repeater for WiFi. Also, devices are now available that allow you to create mesh networks (about them a little later) based on WiFi. (e.g. FL WLAN 1100 - 2702534). And WiFi allows you to organize the so-called roaming. A network is called roaming when several access points with the same SSID are installed, and the client can move from one access point to another (proper WiFi coverage must be provided), while remaining in the same wireless network.
Trusted Wireless 2.0 also allows you to use devices as repeaters and, moreover, restore communication in the event of a signal break. Those. if the device loses connection, then it is looking for another nearest repeater through which data can be transmitted. Thus, communication is restored, and data begins to be transmitted through the backup channel. Communication restoration takes from milliseconds to seconds - depending on the selected data transfer rate. A similar topology, where communication channels line up through arbitrarily selected repeaters, is called a mesh topology.
In addition to mesh topology, devices with Trusted Wireless 2.0 support point-to-point, star, line topologies.
Due to the high sensitivity level of Trusted Wireless 2.0 device receivers, sometimes nodes are connected not to the nearest repeaters, but to more remote ones. To avoid such situations, Trusted Wireless 2.0 provides a “black list of repeaters” (English parent-black-listing), which defines the nodes with which the connection should not be established. A “white list of repeaters” (eng. Parent-white-listing) is also provided, which indicates the nodes that are preferred for connection. By default, all repeaters are allowed to connect.
WirelessHART also uses a mesh network to which 254 end sensors can be connected.
The nature of the interaction of hosts
Internal data exchange between individual nodes is necessary to maintain the wireless network, regardless of the amount of information transmitted. Thus, the process of adding a new node to the network, as well as the management of existing nodes, plays an important role in terms of ensuring the reliability of the network and optimizing the transmitted traffic.
WirelessHART uses a centralized site management approach. There is a “manager" on the network that sends all requests to nodes and receives responses. Accordingly, this approach creates a large amount of traffic passing through a single network node - the manager.
The same is true for WiFi and Bluetooth. Here, the entire data exchange goes through access points, and if the access point fails, the devices will no longer be able to exchange data.
Trusted Wireless 2.0, in turn, uses a distributed approach. Network management is divided into parent / child zones (parent / child, P / C). The repeater (or the central node of the network) acts as the parent through which other repeaters or end devices, the heirs, are connected to the network. Thus, parents and heirs form a tree structure. The parent is responsible for all direct heirs and is responsible for connecting the new heir. All this information is not sent to the central device, but remains within the parent / heir zone, which significantly reduces network traffic.
For example, if you need to connect a new device to the network, this will happen in several stages:
- device search for the nearest station, i.e. the device will “listen” to the air;
- synchronization with the station selected for data transmission;
- switching to the FHSS algorithm used by this device;
- sending a connection request (eng. join-request);
- receiving confirmation of connection (eng. join-acknowledge).
And all these actions are carried out within the framework of one P / C zone. For comparison, in WirelessHART, using a centralized approach, connecting a new node to the network requires 6-7 commands. For a simple point-to-point network, the join operation will take about 2 seconds, and data exchange will begin in 10 seconds. A network consisting of 100 nodes will require about 600-700 commands for connecting and exchanging data, and it can only start in 25 minutes!
Also, within one P / C zone, the parent device collects diagnostic information from the devices in this zone and stores all this information.
Fig. Parent / child zone partitioning (parent / child - P / C)
Also, this approach significantly reduces network convergence time.
If the network manager is de-energized in a centrally controlled network, then all information about the connections in this network will be lost and the network will be restored for a rather long time.
In a network based on Trusted Wireless 2.0, management processes are performed in parallel in different branches of the tree, which gives significant acceleration during network recovery.
Conclusion
What do we have in total? Trusted Wireless and WirelessHART, although much slower in speed, are not always the most important criteria for industrial networks. Often, wireless technology is needed in order to expand the cable, which is not possible to lay. In such cases, often the task is to transmit discrete and analog signals, and this does not require high speeds. Or you need to collect data from some remote installation that exchanges data via PROFIBUS DP or Modbus RTU - these protocols in most applications are also not demanding for the data transfer speed, but the station itself can be quite far away. WiFi and Bluetooth do not provide long-distance data transfers. And setting up WiFi and Bluetooth at ranges from 1 km is a rather laborious task. Trusted Wireless, on the contrary,
But what is really important for the industry is the reliability of data transfer and its compatibility with existing wireless systems. This is what Trusted Wireless and WirelessHART can boast of - through the use of FHSS and blacklists, they are very reliable and allow for very high compatibility with other technologies.
But this does not mean that WiFi or Bluetooth are not used at industrial facilities. They are also often used, but not much for other tasks. They allow you to organize data transmission at high speed over short distances, for example: automation of a large warehouse or machine room.
Therefore, you cannot give preference to any one technology - each is suitable for its task and most often, they are used together in the framework of a single process control system.
Need help building an industrial network? Visit our website .