Self-Configuring Mesh Network Addresses Challenges Associated with Wireless Monitoring of Outdoor Tank Level Applications
Wireless remote monitoring networks provide industries with the capability to automatically track and control field assets. Increasingly, wireless sensor systems monitor tank levels (and other parameters) and use radio technology to transmit the data to control centers. These wireless systems prove cost-effective by eliminating the need for wiring and trenching, especially in applications covering long distances. This is particularly the case in tank farms.
However, not all wireless remote monitoring systems are the same. In some cases, the radio network limits the control system’s effectiveness in certain terrains. Here’s a comparison of the three basic radio network schemes.
· A 1:1 system is the simplest network. The most basic configuration of this system is a level switch wirelessly controlling a remote pump/valve. This system, basically, replicates the sensor signal (a switch) at some other location. For a simple, unmonitored tank application, this type of system can be ideal. It has the control element but does not have any remote monitoring or historical data capabilities.
· The next level of sophistication is a Star System featuring multiple wireless nodes that send sensor data into a single point. Because the system involves multiple sources of data, the data must be addressed so its source can be identified.
· Mesh Networks are self-forming and self-healing networks where messages are passed from device to device until they arrive at a central point called a gateway. While similar to the star system, mesh networks improve the robustness of communications. Ranges can be greatly extended and obstacles that might impede transmission can be detoured. When hills, buildings and other obstructions block a radio signal, a star system becomes impractical. The use of long- range radios coupled with mesh networking technology resolves the problem with obstacles, provider the installer with options to connect every node to the gateway.
Mesh Network Configuration
Mesh networking is a wireless technology that permits many wireless devices to self-configure into a web-like structure. Each wireless node moves data in a peer-to-peer fashion (from one node to another) until the data reaches the Gateway. The route taken will depend on the situation. A good mesh network will pick the best route from each node to the gateway.
The Gateway is a data concentration point typically connected to a local controller (PLC) or to an Internet device like a cell modem (see graphic 1). Range can be greatly extended due to the multiple “hops” between the remote monitoring/control points and the central gateway.
Three critical attributes of a well-designed mesh network include:
- Data movement in “hops” from device to device as it travels from one point in the mesh to another. This hopping permits lower power data transmissions and placement of devices over a larger area, increasing coverage and reducing installation problems.
- Data may take alternative paths to its ultimate destination, assuring robust operation should a node become lost. Routing paths are constantly “tweaked” by the system to ensure optimal paths to the gateway.
- Nodes self-install into the network. NO configuration is required.
Most mesh networks use three types of devices:
· Gateway – The interface between the wireless system and another network (often the Internet or computer), the Gateway often provides administrative functions to manage the mesh. The Gateway is the “center” of the wireless system.
· Routing Nodes – These are standard nodes that connect to devices. (Devices may be sensors, actuators or computers.) In addition to monitoring and/or controlling the device, the routing node participates in the mesh network. Routing nodes are usually line/solar powered, but battery operation is practical in some cases.
· Client Nodes – Clients perform a subset of the functions of a node. Typically, they send and receive data from the device to which they are attached but do not participate in the mesh. Clients are usually battery powered as the routing capabilities can be power hungry tasks.
In outdoor environments, a wireless system may spread over many square miles. When hills and buildings obstruct a radio signal, a mesh network allows wireless nodes to utilize neighboring nodes to relay or “hop” messages to a central location (gateway) (see graphic 1). Each node determines the “best path” to the gateway based on information derived from nearby nodes. The intuitiveness of the nodes allows the system to automatically adjust to changes so data can take alternative paths when necessary to its ultimate destination.
Mesh Network at Work in Tank Level Application
The self-configuring capability of the mesh network proved essential in the following tank level monitoring application that required frequent network changes.
In the original configuration of a network supporting the wireless remote monitoring of tank levels, eight short-range wireless nodes measured tank levels, checking into a Gateway about 1,000 feet away. Hydrostatic pressure sensors monitoring the tank level, as well as the wireless nodes, were installed at ground level. Four of the nodes were on the “wrong” side of the tank battery and had to transmit “through” the tanks to get data to the gateway. This configuration worked fine until a tanker truck parked between the tanks and the gateway. With the tanker in the way, one or two or the nodes on the far side of the tank battery could not directly reach the gateway.
The problem was solved by solar powering one of the nodes on the near side of the tank battery, allowing it to automatically forward messages, if necessary. When the truck was not present, all nodes would check into the Gateway directly. When the truck came to offload oil and blocked some of the nodes on the backside of the tank battery, those nodes would automatically reroute (see graphic 3) their message path through the always-on node on the front. Once the truck drove away, those nodes reverted to direct communications with the Gateway.
Without the mesh networking capability, the wireless remote monitoring and control system would not work under varying circumstances. No configuration or setup is needed with a true mesh system as it operates automatically, freeing the installer of complicated RF worries.
The Outdoor Challenge
In outdoor applications that monitor assets such as tank levels, operators often do not have control over the location of wireless nodes or what might be between each node and the gateway. Having a robust mesh capability can greatly help with this problem. The unique network also enables clever monitoring schemes.
For example, in monitoring outside assets such as oil wells spread out over several square miles, it is unlikely that all wireless nodes at each well will be able to reach a central Gateway. Placement of high-power, long-range node along with low-powered nodes that can operate in hazardous areas will (automatically without configuration) connect to the Gateway through the long-range node The use of a mesh network allowed the wireless nodes to utilize neighboring nodes to relay or “hop” messages to a central location (Gateway).
Amin Shadmani
With the sunset of 2G and 3G mesh network solutions can be a game changer!
Scott - nice article and definitely agree with your critical attributes for mesh, however, I would also include the ability to handle radio interference and OTA updates. Replacing sensors in the field because they can no longer efficiently route data or because the device software needs to be updated is costly.