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What Is an RTU and Why Do I Need One?


December 23, 2021


If you're in contact with the telecom and IT worlds, you must have heard of the acronym "RTU." In this article, we'll try to answer: what is a Remote Terminal Unit (RTU) exactly?

Skip this article and browse our RTUs.

Let's walk through the basics of this important remote monitoring technology.

Problems that Arise Without RTU Visibility

First, let's start with why you'd need a remote monitoring device like an RTU at all.

If you're reading this, chances are that you probably have one - a few - or maybe even a hundred remote sites that you need to keep track of. They might be wireless phone towers or power substations, server rooms, or just about anything else really.

These are unmanned locations; so there's no one there most of the time. You could have an equipment failure, runaway temperatures, or a break-in - but you'll only know what happened after something affects your actual service delivery, something goes offline completely, or your customers call and complain.

This can get expensive very quickly.

You have to respond in a panic, you can lose customers, and you might even face government fines and penalties (depending on your industry). Also, even under normal circumstances, you can waste drive time traveling to and from sites when you really didn't need to.

So, what's the solution?

You need some kind of rugged electronic device with attached sensors that will reliably sit out at your remote site and monitor what's going on. It will then be able to tell you when something's wrong is happening - so you can understand and fix the problem while it's still small.

That's what an RTU is: it's a Remote Telemetry Unit or Remote Terminal Unit. It's a unit that you install at a remote site to inform you about alarm conditions.

RTU means Remote Terminal Unit, but it can also be called Remote Telemetry Unit or Remote Telecontrol Unit.

Remote terminal unit
An RTU is a remote device that monitors and reports events occurring at a remote site.

Explaining the "RTU" Acronym

To better understand the definition of an RTU in terms of remote monitoring, let's break down the acronym.


An RTU is a device that you install at a remote location to monitor the other equipment you have there - plus relevant environmental values, such as temperature, humidity, and water leakage that have a direct effect on electronic equipment. There's not much reason to have an RTU where you have full-time staffing, because those areas are already covered by attentive personnel at all times.

Telemetry or Terminal:

This device is going to act as a terminal for telemetry information. The alarm data that's sent to you is known as "telemetry." It's a terminal device in the sense that data is collected from individual pieces of equipment, aggregated at the RTU, and then sent to you using your chosen communications method.


Unit simply means that an RTU is a single device that performs the functions described above.

Learn the differences between remote telemetry units and programmable logic controllers.

The Inputs and Outputs on an RTU

The inputs on your RTU is what allows it to be your eyes and ears in a remote location. Through its inputs, it can get information from remote equipment and the remote environment in order to trigger an alarm.

When you get an alarm notification, control relays on your RTU allow you to take action and send commands to your remote equipment in order to fix the situation in a timely manner.

Most RTUs have the following three basic input and outputs types:

  1. Discrete inputs
    Discrete inputs give you on/off or yes/no information, such as whether a door is open, a smoke alarm has been tripped, or a generator is online.
  2. Analog inputs
    You also have analog sensors, which can answer "how much?" questions. For example, "How hot is the site right now?" or "How much generator fuel do I have left?"
  3. Control relay outputs
    Finally, you have control relay outputs that let you remotely take actions like pressing a button or flipping a switch. You can use these to turn on backup systems, activate lights, unlock doors, or do just about anything else. An RTU that includes remote control capability reduces a multi-hour journey to a remote site to a simple mouse click - or even a fully automated response.

You will end up wasting money if you don't choose and deploy the right unit to fit your site. You need to choose a model that has the right balance of inputs and outputs for you.

How Do RTUs Collect and Transmit Information?

RTUs collect information from their local environments in several ways.

First, the gear that forms the backbone of your network will generally report problems as they occur. These reports take the form of discrete contact closure alarms on more-detailed protocol messages.

Second, your RTU may have onboard and external sensors that measure level like temperature and humidity. Also, important technical values like battery and tank levels and power voltages may be monitored.

Once your RTU has collected important information, it needs a way to tell you about it.

First, you have to choose one or more communication channels. In many cases, you'll simply use LAN/Ethernet. For more remote sites (or those with legacy tech), you might use another method, such as a dial-up modem, wireless GSM/CDMA, or dedicated RS232/RS485 serial.

Once the channel is set, your RTU will use a protocol to send status information. One of the most common is SNMP - short for Simple Network Management Protocol. This is common on RTUs designed for either Telecom or IT environments. Directly-monitored RTUs can use HTTP/HTTPS to provide an on-board web interface that you can access from any web browser on the network.

Supervisory Control and Data Acquisition (SCADA) system RTUs will tend to use DNP3 or Modbus to talk. Many older RTUs use a vendor-specific proprietary protocol that is compatible only with other monitoring equipment from that same vendor, or with multi-protocol devices.

Learn the differences and similiraties between SCADA and Distributed Control Systems (DCS).

How Will an RTU Let Me Know what's Going On?

With telemetry data logged from your RTU and sent as I described above, how will you receive information so you can take action?

After collecting alarm data and sensor measurements, your RTU will communicate with you (or present data on request) in a variety of ways.

If you have just a few RTUs, you can monitor each unit using increasingly common web interfaces that describe events collected by just one RTU at a time.

The best RTU units out there will give you other options to monitor your network. You'd be able to not only access a web communication interface via PC but also via smartphone. You can even get automatic phone calls, text messages, or emails that describe the problem in detail. Also, alerts can be limited to the most important problems, this way you won't constantly be woken in the middle of the night by a smartphone screen filled with too many alarms to interpret.

What If I Need Multiple RTUs?

As stated above, if you have just a few RTUs, you can choose a model that will directly email or send you a text message.

However, in the real world, most companies have numerous RTUs. If that's also your case, then it's better to have a central master server that collects data from all of your units and displays it on one screen for you and the rest of your team. In other words, the central master station will collect alarms from all your RTUs, then it'll summarize all detected problems in a single, convenient interface.

Virtually all RTUs will have some method of sending data to a central master console. This can take the form of many different protocols and communications channels (and protocols can be either polled or asynchronous), but they all accomplish the same function: you can view data collected from your entire fleet of RTUs in one central office.

This way, you can have your master station send you a text message, email, or even recorded-voice phone calls to alert you to serious problems.

How Can I Choose a Perfect-Fit RTU?

If you've decided to invest in an RTU to solve your visibility issues, there are some things you need to consider in order to get the right balance of capacity, interface, and features - and to ultimately know what you really need.

Your first step is a complete survey of your current network and remote sites

It's important to select an RTU that not only meets your current requirements but is also compatible with your existing network transport.

Take a look at some questions that will help you start your network monitoring inventory:

  • How many remote sites need to be monitored?
  • What protocol and transport methods do you need to support?
  • How many alarm points do you need to monitor at each site?
  • How much rack space do you currently have available?
  • What dedicated facilities do you already have in place to transport data?
  • How many ASCII devices (e.g., switches, routers, etc.) will you monitor at your remote sites?
  • What type of power do you have at the master and remote sites?

Also, before you select an RTU, think about what your ultimate goals are for your network monitoring.

The following is a list of questions that will help you form your future network monitoring plans:

  • How many alarm points will your network alarm system monitor in the next 5-10 years?
  • What alarm monitoring features will you need - discrete alarms, analog alarms, controls, serial ports, local visibility?
  • What kind of data transport do you want to use, now and in the future - overhead channels, terminal servers, LAN/WAN, other?
  • What protocols will your remotes use? Are you planning to shift your monitoring to a standard protocol like SNMP?
  • How do you want to mount your RTUs? (23" rack, 19" rack, DIN rail, wall, tabletop)
  • What type of alarm termination works best for you?
  • How do you want to receive alarm notifications?

What RTU features do you need?

Now that you have taken a look at some of the most important factors involved in deciding which RTU to choose, let's take into consideration some essential features that any high-quality unit must offer.

Here's a list of must-have capabilities you should look for. If a device can't meet these basic requirements, cross it off your list.

  • Key alarm presentation and notification functions:
    SMS and email notifications
    Detailed alarm notifications
    Alarm correction instructions
    Web interface
  • Essential alarm sorting and analysis functions:
    Alarm sorting
    Nuisance alarm filtering
    Custom combination (derived/smart) alarms
    Root cause analysis
    History and trend analysis
  • Critical alarm collection and device management functions:
    Live analog monitoring
    Control relays
    SNMP support and ping alarms

How will alarms be transported to your specific control office?

Another very important aspect to take into consideration when deciding upon an RTU is looking at how alarms will be transported back to your control office.

Once alarm data has been collected at your remote sites, it needs to be transmitted over a data network to your alarm presentation master. There are two things you should keep in mind about RTU alarm data transport:

  1. As much as possible, you want to work with transports that are already available in your network. You don't want to create added expenses by committing yourself to install new network infrastructure. It's best to choose a device that is compatible with the transport you already have.
  2. It's a good idea to have a secondary backup path for your alarm data in case your primary path fails. No transport is 100% reliable, and you don't want to lose alarm visibility of your revenue-generating network under any circumstances.

How big is your network?

It's also essential to note that the size of your network will determine the needs and requirements of your RTUs.

  • Small:
    Select a small remote alarm unit, such as the NetGuardian 216, for cell towers, remote huts, or enclosed cabinets (16 discrete alarms, 2 analog alarms, SNMP).
  • Medium:
    Select a medium remote, like the NetGuardian 832A, for remote switches (32 discrete alarms, expandable to 176 discrete inputs, 32 ping alarms, 8 analog alarms, 8 control relays, 8 serial terminal server ports, SNMP).
  • Large:
    For central offices or regional hubs, select a large RTU, such as the NetGuardian 480 (80 discrete alarms, 16 ping targets, 4 control relays, SNMP).

Let's Work Together on Your Remote Monitoring Project

With the information collected by your RTUs, you can maintain excellent situational awareness and react perfectly to remote threats.

However, no RTU is quite like another. Many different models exist to give you flexibility as you plan your monitoring system. You shouldn't buy less alarm capacity and sensor inputs than you need, or you won't get a complete picture of your network status after you deploy your brand new system.

You also shouldn't buy tremendously more capacity than you'll ever be able to use, or you'd be wasting your budget without the hope of a return. You need to find an RTU that has a bit more capacity than you need right now, so you have room to grow.

This all falls not only on the RTUs you've decided to roll out at your sites but also on which vendor you've chosen to purchase from. In order to make a good decision, you must always choose to buy from remote monitoring experts - as quality can vary widely between manufacturers.

DPS is a trusted provider of monitoring and control solutions for over 30 years, so we are experts on designing a reliable system for collecting and managing your alarm and control information. Our engineers have the design experience required to make sure your RTUs are a perfect fit for you.

Remote monitoring expert
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If you want to know more about how you can monitor your remote sites, download our SCADA Tutorial White Paper.