You've decided it's time to buy an RTU to monitor your remote sites, but how do you decide which model is the best fit?

Let's take a look at the top 3 things you need to think about when you're choosing an RTU.

The First Of Our Three Important Considerations: Capacity

The RTU capacity breaks down into a few key types:

1. Discrete inputs

   These are simple on/off binary type inputs. They’re used for things like door sensors, motion sensors, and especially for equipment that will self-report alarms using contact closures.

2. Analog inputs

   They are for continuous range type values. Some examples are: what’s the temperature in the room, what's the humidity, how much fuel do I have left in my generator propane tank, what's my battery voltage and therefore what's my expected battery life remaining.

3. Control relay outputs

   These are used for the RTU to command other equipment to do certain things. You might be able to turn something on, turn something off, open a door, there's almost no end to what you can do with a control relay output.

What you need to do is go out to your site, look at everything you've got, and decide how many of each of those three things you need. Once you've done that, add about 15% to those counts, because you need to allow room for reasonable future growth.

The whole point of RTU capacity is splitting the middle between the hazard of running out - and not having enough once you need it - and the hazard of buying way more than you need and wasting your budget.

The Second Consideration: Power Input Voltage

Power input voltage is just as important for your RTU as it is for all of the rest of your gear.

You need to know what voltage you're running at your site and then choose an RTU with an input voltage that matches. I see a lot of -48V DC and +24V DC. If you're at a solar site, for example, you might have +12V. If you're in a data center or a server room type environment, it's very likely that you'll just want to run directly off of AC.

If you don't get this right, you'll be stuck buying a transformer later. This not only wastes budget money, but also adds a point of failure to your system that doesn't need to be there.

Our Third Consideration: Build Quality And Overall Reliability

Quality and reliability are a bit harder to pin down than something like capacity or voltage, because they aren't just numbers.

However, I'll give you some questions that you can use when you're talking to manufacturers. They'll help you gain key insights into what you might expect.

1. Where do you do your engineering and where do you do your manufacturing? Is it something that you handle yourself, is it done by another company, is it done in another country?

2. What kind of testing and measurement do you do before you have unleashed this product on the marketplace?

3. Do you have a temperature chamber so you can test how the product performs in the very hot and the very cold?

4. Have you done EMI testing where you see how much interference comes off of the product and therefore how much interference it's expected to absorb?

5. Have you done under and over voltage testing to make sure the power supply doesn't just fry?

6. How long have you been in business?

   Note that there's no guarantee the company that's been around for a long time is any good, but it's very hard for a brand-new company to have developed the experience necessary to give you really high quality and really high reliability.

7. And, finally, how many of these products have you sold and who bought them?

   There's nothing better than a client list when it comes to knowing that what you're purchasing is proven technology and that you're not just the guinea pig.