Moving to a wireless remote monitoring system

09 July 2017

Scott Keller offers advice on what needs to be considered when moving from a wired remote monitoring solution to a wireless one.

Having the ability to automatically track and control assets remotely is an important requirement in many applications and it can help to improve operations while reducing costs. The use of wired remote sensing systems are the most usual solution to achieve this, especially in the oil and gas industry. Sensors monitoring various assets are normally equipped with outputs that require hundreds of metres of wire to connect to a PLC.

Analogue 4-20mA current loop and Modbus interfaces are examples of communication protocols that can cope with long cable runs.

However, while wired remote monitoring offers advantages over manual readings from sensors or gauges, it does have limitations, depending on the application regarding installation cost, sensor flexibility, and environmental influences. If a remote monitoring application requires multiple sensors to monitor various parameters, for example, a wired system requires each sensor be wired back to the controller using an interface port. For large systems, a wired system requires a large interface panel with many different interfaces.

A wireless system, however, will often have a digital communications interface (Modbus RS485), allowing for many sensors to be wirelessly ‘connected’ to the controller through a single port. While beneficial when configuring a new controller, changing from a wired interface, with lots of individual input ports, to a gateway-based wireless system with a digital interface does require pre-planning.

In lieu of making a complete changeover there are modules available that can convert digital information into individual analogue channels, simulating the existing analogue interface. Although this is the easiest solution for a quick changeover, and does not require any software changes, it does not utilise the vast increase in data and diagnostic benefits that are made possible by changing the complete communications architecture to a wireless sensor control system.

Factors which should be considered when evaluating a move to a wireless remote monitoring and control system instead of upgrading an existing wired system:

Costs
Wired systems: What is the area over which the wired system will operate?  Costs related to running conduit over large areas, especially if requiring trenching, can make a wired system too cost prohibitive.

Wireless systems: With no conduit or trenching requirements, a wireless system can be installed at the cost of a wired system with 15m of installed conduit – less if conduit needs to be buried.

Maintenance

Wired systems: When removing sensors for periodic maintenance, wires integrating to units can be damaged. Improper wire labeling can result in incorrect sensor replacement.

Wireless systems: In a wireless system, nodes integrate to sensors that send data directly to a gateway. When removing sensors for maintenance, the wireless node easily detaches and re-attaches without interference by wires.

Environmental

Wired systems: Underground conduit is often ruined by equipment when digging a trench for another underground conduit run. The cost to replace conduit and cable systems can be huge. In addition, lightning strikes on a sensor will propagate along all wires, often destroying equipment attached to the system.

Wireless systems: With no underground wires, nothing must be dug when going wireless. Once installed, lighting strikes to a sensor may damage the single unit, but not interfere with the complete system.

Topography 

Wired systems: Certain locations make it impractical to run wires, such as across a highway or river.

Wireless systems: A wireless node can be easily installed on the other side of a highway or river.  Self-configuring, wireless nodes automatically connect to the network.When moving from a wired solution to a wireless one, consider all the aspects of the job. Is there a problem with what you have now? If so, are you willing to change the interface at the controller understanding that this change will allow you to take in much more data and diagnostic information than you had before? Is it more cost-effective when considering the absence of cable, trenching and interface requirements? Deciding when to ‘pull the trigger’ is always the hardest part.

Scott Keller is CEO at SignalFire Telemetry.