Product Review: Rosemount 644

Come with us back into the vast realm of temperature measurement! We’ve covered this topic in some depth already, but it has so much more information we have yet to review. We’ll probably revisit this universe several times.

I have to say I enjoyed calibrating temperature sensors back in the day. I spent many lab hours receiving devices from the field for calibration. For this work, you must have a lot of patience. Drying ovens take time to achieve the proper conditions. Today, calibrators can detect automatically when the drying oven is ready. When I was in the field, I had to take notes and create a report with the data manually. Of course, some companies still do it this way today, but modern technology can help with these activities too.

So let’s talk about the device we’re gonna review today. Emerson Automation Solutions brings us the Rosemount 644, a flexible transmitter that offers different housings and local configuration. Let’s see how it can support you! If you have experience with this device, let us know here or in our social media.

But before we hit the product review, time to poke you about the Visaya newsletter again! Come on. If you haven’t signed up, then you’re missing our weekly content! We send our insights and experiences on the monthly topic straight to your inbox. Just plop your email in the box there and we’ll do the rest. Won’t hurt a bit, promise.

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 644 is a device with many faces – but in a good way! We’ll get into that in a minute. If you don’t want to spend a lot on fancy devices, then you should take a look at this simple transmitter.

You can choose an LCD display with or without local configuration. The local configuration has two push buttons that allow you to set up the device without a specific tool. You can also password-protect the configuration, a nice little security layer. The display without the local setup has 11 digits in 2 lines, and the one with the “Local Operator Interface (LOI)” has 14 digits in 2 lines.

Rosemount 644
Courtesy of Emerson Automation Solutions

As for the many faces, it comes with different housing styles – field mount, head mount, and rail mount – with an assortment of approvals and materials to cover a wide range of applications. You can also choose a dual sensor input if you have the head mount or field mount version.

What can it do?

The 644 can accept resistance temperature detectors (RTDs), thermocouples, millivolts, and resistance as inputs. The millivolts and resistance inputs give it a wide range of applications. That means you can measure any variable, not just temperature. And it offers the option of dual channels in your field device.

Rosemount 644
Courtesy of Emerson Automation Solutions

For integration, you have HART over analog, FOUNDATION Fieldbus (FF), and PROFIBUS PA (PB). One of these common protocols should fit your system, and for an entry product this list is more than enough! If you need a different protocol, then Emerson has it for you – just not in this device.

Depending on your segment, you may have special requirements your device must meet. The Rosemount 644 is an SIL2/3-certified device with approvals for hazardous areas and marine applications. Plus, you can get a polished stainless steel housing for sanitary, biotech, and pharmaceutical applications.

Why should I care?

You can’t expect too many features from a simple temperature transmitter. However, the 644 has a few nice options to discuss in this review. Keep in mind you’ll have to ask for these if you want them on your device.

The Hot Backup™ is an outstanding feature here. If you have two sensors connected to the transmitter, the Hot Backup can switch from one to the other automatically if one fails. And during normal operation, if you have a drift between the sensor measurements, the transmitter will detect it and notify you to avoid a future failure. Nice, huh?

Rosemount 644
Courtesy of Emerson Automation Solutions

Another good feature is the thermocouple degradation diagnostic. The transmitter will monitor the health of the thermocouple and inform you of any degradation, obviously. It’ll also record minimum and maximum temperatures. You can use this data to check whether the sensor experienced high temperatures in the process or the environment.

The device description (DD) of the Rosemount 644 gives you an easy dashboard with intuitive configuration through the plant asset management (PAM) system.


You have a surprisingly long list of features with the Rosemount 644. This simple device from Emerson could help in multiple ways, so scale it out to see if it’ll fit your process and your budget.

If you want to learn more about this device, you can watch Emerson’s video:

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