Many different industries use remote systems for machine monitoring, predictive maintenance, vendor managed inventory, building automation, and energy management. By monitoring operating conditions such as level, flow, and vibration as well as ambient conditions such as humidity, temperature, and moisture, remote monitoring systems serve a crucial role in ensuring the optimum operations and security of unattended equipment and unprotected assets at distant locations.
While many remote monitoring systems are now Internet-based, communications through plain-old telephone service (POTS) is not dead! Phone-line-based remote monitoring unit (RMU) communications remain a viable alternative (or complement) to Ethernet and wireless communications in a variety of remote monitoring applications where a broadband connection is impractical or power outages prevail (see the figure).
Having survived numerous assaults from competing technologies such as ISDN, cellular, and wireless services, the phone line is considered the cockroach of the communications world. It’s hardened, reliable, pervasive, and resistant to cyber-attacks. Often, it’s the only form of communications available during natural disasters. It even works during power outages. While global phone-line installations decreased from 1990 to 2010, their numbers have stabilized and are increasing in some areas.
Traditional Approach, Modern Conveniences
Except for bandwidth, monitoring systems based on phone lines can mimic the functionality that Internet protocol (IP) and wireless communications have to offer. Their information can be accessed through a browser or smart-phone app. Also, their data can interface with cloud-based mapping and database services.
Costs are generally less too. If the monitored location is already wired, it can share an existing line. If the building is not wired, the installation of a new phone service is less expensive than the installation of new data service. Setup and operation of a phone-based monitoring system is easy, whereas attaching to an existing data network may involve the IT department.
Criteria For Choosing Phone-Line Communications
No one can deny the many benefits that IP and wireless communications have to offer, especially in terms of bandwidth and connectivity. But in the real world of remote monitoring, you may encounter obstacles to IP and wireless communications that are easily circumvented by the use of a phone line.
Consider an application that involves equipment in numerous unattended buildings dispersed over a very large geographic area. Connecting the remote monitoring system to a IP or wireless communications network can be as difficult as trying to get an IT department to punch a hole through its firewall, while establishing phone line communications can be as easy as a phone call to the local phone company. Although every site can present its own unique set of installation issues, the cost and difficulty of installing a phone line is fairly constant.
Wireless communication presents the additional concerns of coverage gaps (especially in remote areas) and service degradation due to weather, foliage, or new construction. Any communications method is subject to service interruption and dispatching a service technician can be very costly, whereas problems related to the phone line are the responsibility of the phone company.
If your business operations rely on data collected from monitoring systems at remote sites, you need to consider the impact of events that can instantly cut you off from all of your remote sites for an extended period of time.
Orchestrated attacks on communications networks are a growing concern. These attacks may be directed specifically at your organization or at the country in general, and they can cut you off from all of your remote locations. Phone lines are less susceptible to such attacks.
A far less nefarious concern, especially for IP and wireless remote monitoring systems, is the reliability of the chain of custody of your data as it moves from your remote site through an ISP, through various third-party cloud services, and through a server to your browser.
A break in any link of that chain, whether it’s due to a hardware fault, software glitch, or something else, will impact your entire network. A remote monitoring network based on phone lines gives you the insurance of being able to bypass that chain of custody and collect data directly from the remote monitoring system.
A Practical System
A landline based monitoring unit such as Global Monitoring’s GMU 8100 ships with a landline voice-modem that is compatible with most public phone systems found throughout the world. Ideally, the remote monitoring unit should be the only device on the line, but it’s possible to share a line with a fax or telephone. Connections are made simply by inserting the phone cord into the mating connector located on the remote monitoring unit. The other end of the phone cord is attached to an active phone jack.
The GMU 8100 uses the landline connection to report information directly to any fax or modem-equipped PC without the need for a server or costly third-party service. It also vocalizes information to any landline or cell phone. The monitoring unit can report information via landline to a server that can process and store data and provide reports to any device with Web access as well. Data rates are standard phone line rates up to 53 kbits/s.
The Global Monitoring unit has eight analog inputs that accept 4 to 20 mA, dry contact, and 0- to 5-V dc sensors. Up to 24 additional inputs can be added in blocks of eight. Each input accepts a voltage signal. Selectable input ranges from ±1 V dc to ±10 V dc. The unit can also accept dry-contact and 4- to 20-mA signals using external resistors. The inputs have 14-bit resolution. Features include scaling, data logging, alarm triggering, and more. There are four output relays that can be controlled either manually or automatically as a function on input set points or alarm status.
The GMU 8100 supports 12 distinct modes for remote communications plus two direct modes for local communications. Standard modes include landline to PC, landline to fax, landline to voice, and a RS232 port for local access. Optional communication kits are available for wireless and Ethernet connectivity
Final ThoughtOf course, phone-line communications aren’t ideal for all remote monitoring systems. But for mission-critical applications that require IP communication, you can always augment a broadband connection with a phone line. So don’t consider telephone lines obsolete. They might be the right answer for a quick, easy, and cost-efficient installation.