PART 3 – Remote monitoring of tailings dams Q&A series: Worldsensing installation and operations

In the third installment of our Q&A series based on the Worldsensing webinar on IoT remote monitoring of tailings dams, now available on demand, Vincent Le Borgne and Juan Pérez Arcas answer your questions on Worldsensing installation and operations.

Using a SIM [subscriber identification module] card with the gateway, can you automatically push data to an FTP [File Transfer Protocol] site at a preset interval, such as every hour?

Juan Pérez, geotechnical engineer, wireless monitoring expert and product owner of the leading system for IoT-based monitoring, Worldsensing: 

Yes. The gateway has an internal modem and it’s possible to use a SIM card for connectivity. With the single-gateway architecture, the server is ready to push data via FTP. There is no preset interval: the data is automatically pushed to an FTP client after reading or every 15 minutes.

How do you transmit data underground in deep mines? What’s the depth limit of instrumentation systems in underground mining sites? Do you use fiber or have a wireless mode of transmission to transmit the data outside or to surface base stations? 

Juan Pérez: 

Worldsensing nodes are ruggedized and have been tested in temperatures ranging from -40ºC to +80ºC, so they can withstand harsh environments such as underground mines. We are open to projects to test the depth limits of our monitoring system and to understand how ambient conditions may impact the network quality in deep underground mines. The Worldsensing laser distance meter node can be particularly useful for convergence monitoring. 

Worldsensing nodes can also read multi-point borehole extensometers, pressure cells and other frequently used sensors for underground monitoring. Worldsensing may be used as a last-mile solution inside deep galleries. The nodes wirelessly send data to gateways underground that are connected to fiber-optic points used for machinery control and cameras, in order to transmit the data to the surface.

Can existing data loggers be integrated into this system?

Juan Pérez: 

Not yet. While you may connect LoRaWAN devices from other manufacturers, it is not possible to integrate data loggers using communication technologies such as RSTAR from RST Instruments or GeoNet from Geokon. Worldsensing is working with partners to validate and integrate LoRaWAN devices that can offer new applications on top of our solution, for instance for tracking workers and small machinery.

When using multiple gateways to reduce data loss, is your software capable of combining data from multiple nodes?

Juan Pérez: 

If you are using multi-gateway networks, yes. The radio network server combines radio messages from multiple nodes, which avoids data duplicity or conflict. If you are using a single gateway it is possible to minimize data loss by installing an uninterrupted power system or a battery backup. 

Do you need to use repeaters when a tailings storage facility is at the back of waste dumps and the office is on the other side? 

Juan Pérez: 

No. In the setup you described, we recommend the gateway is installed at a higher position than the waste dumps and is positioned with line of sight to the tailings dam. The gateway has an internal cellular modem and an Ethernet port so it can be connected to the mine network. It is important you position the gateway like the antenna of the system. If communication towers for cellular and voice radio communications are already deployed in your mine, these are ideal locations for the gateway because they have a power supply and connectivity.

Are shape arrays compatible with your logger station? 

Juan Pérez: 

Shape arrays are currently not compatible with Worldsensing. We are already working on this integration so I hope we’ll be able to share good news soon.

The wireless nodes allow you to connect at most six sensors. Is there a node that allows more sensors, considering dams, such as concrete-face rockfill designs, that have a lot of instrumentation?

Juan Pérez: 

It’s true we currently don’t have nodes with more channels. We have a five-channel vibrating wire node and a four-channel analog node. In addition, our digital node can read chains of up to 30 digital sensors, or up to 50 using external power. Let us know about your monitoring needs for concrete-face rockfill dams and I’m sure we’ll find a solution.

Can LoRa be used in a concrete structure or is it too sensitive to barriers?

Juan Pérez: 

It is possible to cross some obstacles with LoRa. For instance, some Worldsensing nodes are installed on the floor -7 of a building in Paris and the gateway is installed at ground level, receiving the radio messages. However, if there is a thick mass of concrete, like in a massive concrete dam, or rock, like in underground mining, wireless should only be used in galleries.

Can nodes act as relays when remote nodes cannot directly see the gateway, like in a mesh network?

Juan Pérez: 

No, Worldsensing doesn’t use a mesh network. We use star networks. The sensitivity of the radio means a node does not always have to see the gateway and can overcome some obstacles. Saying this, we always recommend installing the gateway at a high point to improve the range, especially when nodes don’t have line of sight.

Can gateways also be connected to instruments or are they for data transmission only?

Juan Pérez: 

No, it is not possible to connect instruments to gateways. Gateways are used for data transmission only. In fact, a gateway is the antenna of the wireless network. This is why it should be deployed at a high point, like a communication tower. Gateways are typically located far away from any geotechnical or structural sensor.

Do node data loggers store multiple readings onboard and then transmit them or do they transmit single readings?

Juan Pérez: 

Due to the low-power consumption of the transmission, digital nodes or node data loggers transmit each reading after the measurement, providing near-real-time data.

What is the maximum interval at which data can be collected using a Worldsensing monitoring kit?

Juan Pérez: 

Currently, the highest possible acquisition rate when using Worldsensing is one sample every 30 seconds, and the lowest is one sample every 24 hours.

What can be installed on the node to increase the radio range?

Vincent Le Borgne, mining R&D manager: 

We used a heavy-duty regular omnidirectional antenna that broadcasts evenly in every direction. Regular antennas with 15-kilometer ranges are usually more than enough for most of our applications, but in theory it would be possible to use a directional antenna.  A Yagi antenna is the most common type. It’s not something we often have to use.

Can you comment on maintenance and troubleshooting requirements, especially during initial scale-up at remote mine sites? What is the required maintenance? Could it be done with internal skilled employees?

Juan Pérez: 

Maintenance is minimal and depends on where the node is located. After a short introduction and basic training, every employee is able to maintain the nodes and gateway and manage the data through a mobile app. A monthly visual inspection is good practice, particularly in areas with activity. In addition, we recommended you inspect the node and sensor cables after detecting anomalous or missing readings. To minimize manual maintenance rounds, we also recommend you invest in software that can show the status of the network and trigger alarms in case of downtime. 

Finally, another important maintenance requirement is batteries. Although batteries may last up to 10 years, it is good practice to schedule changes based on the battery life estimates and frequency of data acquisition. 

Can you mention some instrumentation reliability assessment options during operation, when working from a distance?

Vincent Le Borgne: 

The nodes themselves are reliable and have posed no issues. The upcoming multi-gateway platform will also address possible issues on connectivity or data loss by allowing for redundant gateways on projects.

Juan Pérez: 

The Worldsensing system provides detailed information about the reliability of the wireless network. All radio messages include a sequence number, so it is possible to identify the quantity of received and lost messages in total and in each of the previous five days. In addition, information related to the signal strength is available. 

On the other hand, and related to the reliability of the sensor measurement, the Worldsensing nodes include internal checks to transmit verified readings when this is possible.