Product Review: Rosemount 248 Wireless
Temperature measurement can challenge even seasoned pros. I posted an article on how to integrate temperature sensors or transmitters into control systems and the pros and cons of each method. Why? Because I’ve seen companies choose old solutions for new projects because they simply didn’t understand or even know about new options. In some cases, a lack of preparation or structure prevents new options from working, so good old analog seems like the easiest choice to make. You can read more here.
And now, back to the show! Our buddies from Emerson brought us the Rosemount 248 Wireless Temperature Transmitter. Let’s take a look at the features and see how this device can fit in a new process.
Disclaimer: This product review examines only features, not performance. If you’ve used this device, feel free to share your experience in the comments.
Whatcha got there?
The Rosemount 248 has a design that stands out from the other options on the market! First, it has the new concept of the wireless transmitter, with an antenna inside instead of outside the housing. Second, even with the compact design, you can still fit in a local LCD display and a simple internal connection.
The field operator can use the local display to read the process variable, diagnostics, and battery life. However, you can’t set up the transmitter locally! You have to use a HART field communicator. Sad. But as soon as you connect the device to the network, you can do all your adjusting remotely. Much better.
Another drawback: The internal antenna limits your housing materials. The Rosemount 248 uses polymer to avoid attenuating the wireless signal. Even with this limitation, the device has enough approvals to cover a number of harsh and hazardous environments. Oh wait, I found another version of the 248 with an external antenna and an aluminum housing! But we’ll stick to the compact version today, okay?
On the up side, the Rosemount 248 can read resistance temperature detectors (RTDs), thermocouples, resistance, and millivolts. On the down side, it only has a single sensor input, limiting you to one sensor. But how much can you expect from a device on the budget end of the line?
What can it do?
Beyond the obvious, not a whole lot. Still, the Rosemount 248 offers good possibilities for temperature measurement. You can also read different field sensors with the resistance or millivolts output. Then the device can send you values in resistance, millivolts, or percentage of the measurement range.
And what about its accuracy, you say? Well, that varies according to the sensor you connect. For instance, the Pt100, with a range from -200 to 550 degrees Celsius, has an accuracy of +-0.45 degrees Celsius. The type-R thermocouple, with its range from 0 to 1768 degrees Celsius, has an accuracy of +-2.25 degrees Celsius. You can find the entire sensor list on the datasheet, or you can click here to find more information.
As for protocols, you only get WirelessHART. That’s okay, though! This open protocol lets you connect the 248 to any WirelessHART network, giving you a bunch of wireless options! Moreover, the device’s battery can last up to 10 years. An online tool called the Power Module Life Calculator can check your potential battery life. For example, if you set an update rate of 8 seconds on a well-formed network in an environment of 30 degrees Celsius, you could get 4.5 years of juice!
Why should I care?
Because it could save you money, duh. The Rosemount 248 has a lot of embedded technology for a low-end device. If you already have a WirelessHART network, then the 248 will do you right.
Better still, the device has an impressive battery life, especially if you tweak your numbers. Sure, you can get more than 4 years working with 8 seconds, but you can set it up from 1 to 60 seconds. If you have a fast process, then you should probably keep your update rate in seconds. But a pokier process that can use an update rate in minutes can stretch your battery quite a ways! (Let me remind you here that update rates affect the number of devices the network will support too. Faster update rates mean fewer devices.)
Anyway, the 248 can offer you diagnostics and extra data as well. Nothing fancy, of course, but at least you can access it all remotely. Failures, maintenance needs, and other stuff will show up on the gateway web server, device management software, or control system.
In general, the Rosemount 248 is a simple device, but its advanced embedded technology brings it up a notch. No fancy diagnostics, just easy integration and remote access to a little extra data. Worth thinking about.