SCADA systems are used in a variety of industries to monitor and control process. A typical SCADA system includes a number of RTUs (Remote Terminal Units) which are connected to various field devices. The RTUs collect data from the field devices and send it back to the centralized SCADA system for monitoring and control.
A SCADA system specification will usually include an RTU specification. The RTU specification will detail the requirements for the RTU, such as its communications capabilities, input/output (I/O) capabilities, and other features.
Other features that might be included in an RTU specification include:
When designing or selecting an RTU for a SCADA system, it is important to carefully review the RTU specification to ensure that the RTU meets the specific needs of the application.
When you're talking about general-purpose SCADA equipment, inputs and outputs (I/O) are the most basic of any spec list.
It defines how many and what type of inputs and outputs the RTU will have. For example, an RTU might have eight digital inputs, four analog inputs, and two digital outputs.
In the modern age, I/O also takes the form of protocols. Where a device might formerly have reported to an RTU using contact closures (digital inputs), it might now do that with MODBUS, CANBUS, or some similar protocol.
The introduction of such protocols into the SCADA world means that devices can provide much greater detail while simultaneously lowering hardware costs.
Because SCADA systems have evolved over such long periods, however, it's not unusual to see a SCADA RTU specification that includes a requirement for traditional digital and analog inputs.
The communications specification for an RTU will detail the protocols that the RTU can use to communicate with the rest of the SCADA system. Common protocols include Modbus, DNP3, and IEC 60870-5-104. The communications specification will also detail the physical interface that the RTU uses to connect to the network (Ethernet, fiber, RS485, etc.).
In addition, the RTU should have the ability to support multiple communication channels in order to provide redundancy in case of primary channel failure.
Environmental specifications are important to consider when choosing an RTU, as the unit will need to be able to operate in the specified temperature and humidity range.
For example, if the RTU is going to be installed outdoors, it will need to be rated for operation in extreme temperatures. RTU manufacturers, at least the good ones, will have extensively tested their RTUs in temperature chambers to provide an accurate rating to compare with your required specs.
It's also common to see humidity specifications, such as "must operate in environments up to 80% RH, non-condensing".
Power requirements are also an important consideration. The power specification for an RTU will detail the type of power that the unit requires (AC or DC) and the voltage range.
For example, an RTU might require 24 VDC at 0.5 A, or perhaps -48 VDC at 0.2A.
It's also important to consider certifications when selecting an RTU. There are several certifications that an RTU might need in order to be installed in a particular environment. Common certifications include UL (ETL), CE, and ATEX.
The certification requirements will depend on the specific installation location of the RTU. For example, an RTU installed in a hazardous location will need to be certified for use in that environment.
Many of the most fundamental safety and reliability certifications, like UL/ETL, are nearly universal for any device involved in life-safety applications.
You might get lucky and not need any certifications, but that is something you'll want to know before you buy (not after you buy something that you're not allowed to use).
As we've discussion, an RTU specification will detail the requirements for communications, I/O, power, environmental conditions, and certifications.
When selecting an RTU for a SCADA system, it is important to carefully review the specification to ensure that the RTU meets the specific needs of the application. Choosing the wrong RTU can lead to problems with communications, I/O, power, or environmental conditions. Be sure to consult with a qualified engineer to select the best RTU for your application.
If you're not an expert in SCADA systems, it's a good idea to talk to someone who is. They can help you understand the different RTU specifications and how they apply to your application.
An experienced SCADA integrator will have a wealth of knowledge about RTUs and can help you select the best unit for your needs. They can also help you understand the installation and commissioning process, which can save you a lot of time and money.
At DPS, we have lots of experience with both RTUs and SCADA technology. We can help you evaluate your requirements. That sometimes leads you away from our RTUs and HMIs, but that's normal and expected. The important thing is that you get a second set of experienced eyes on your specifications to make sure you don't make a costly mistake.
At DPS, we have many engineers on staff who can help you kick off your SCADA RTU project with an initial discussion. Be sure to have a copy of your RTU specifications ready when you call so we can go over them together.
Whether it's me or another sales engineer who picks up the phone, you'll be in good hands. We've done a lot of projects. If we get stuck, we have our product engineers literally about 60 feet down the hall. We'll answer all of your questions together.
Andrew Erickson is an Application Engineer at DPS Telecom, a manufacturer of semi-custom remote alarm monitoring systems based in Fresno, California. Andrew brings more than 16 years of experience building site monitoring solutions, developing intuitive user interfaces and documentation, and opt...
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