Product Review: Yokogawa FLXA21

Most of the time a pH sensor needs a field transmitter to read its data and send it through the system. You have a ton of transmitters on the market, some of which can only read analog sensors and others that can read analog and digital. If you want to take a moment to reread our article on scaling out a new pH sensor, go ahead. We’ll keep going, but you can catch up.

For this product review, I decided to go with a basic transmitter. No super-fancy features, just the standard data from the sensor and options to set up the display or more than one output. So let’s start!

Say hello to Yokogawa and its representative of the day, the FLXA21! The FLXA21 is a two-wire analyzer for online measurement, with up to two input channels. Yokogawa has another one like it, the FLXA202, but it’s simpler than FLXA21. We want the FLX21 to have the same level of features as its pending competitor. Wanna guess who that’ll be? Go ahead, leave your best guess in the comments.

Grab a corn dog, have a read, and draw your conclusions!

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?

At first glance, the FLXA21 looks a little fragile, but it’s merely compact, at 144 x 144 x 151 millimeters. Yokogawa promotes its modular nature and multi-channel functionality. We’ll chat about the modules later, but the fine print limits the multi-channel bit, so get out your magnifier if you want to know more.

The device does have some flexibility for its input, reading a variety of sensors and showing all data on a touchscreen display. The FLXA21 can measure pH/ORP (oxidation-reduction potential), inductive conductivity, contacting conductivity, or dissolved oxygen.

Courtesy of Yokogawa

Theoretically you can connect more than one sensor, but of course, reality always comes with its own rules. If you have an application with an inductivity sensor, you can only have one sensor connected per transmitter. Same goes for a digital FU20F pH/ORP SENCOM sensor. Boy, that’s a mouthful. Even if you don’t use either of those, you can only connect the same kind of sensor to the transmitter. Not as flexible as it first appeared, is it?

The modular design does bring a great advantage. If you have a problem with a module, then you can replace it quickly and easily, which helps a lot in field maintenance.

What can it do?

As I mentioned before, FLX21 can measure dissolved oxygen, pH/ORP, inductive conductivity, or contacting conductivity. Just order the right module from the beginning. It has good certifications too, like for hazardous applications and such. You can find the complete list in the tech manual.

As a loop-powered device, you can send power for the transmitter through the signal cable. You also have basic digital protocols here – HART, Foundation Fieldbus (FF), and PROFIBUS PA – to fit the device in most  processes, a bonus point for seamless integration. However, if you need a different protocol, then keep looking.

Courtesy of Yokogawa

You can get it in plastic, stainless steel, or stainless steel with corrosion-resistant coating, so that broadens its application range too. Another cool point to highlight is the language set. It offers 12 languages, so you can probably find one you’re comfortable with somewhere in there.

Why should I care?

Because it’s surprisingly nice for a basic transmitter. You can set it up using the touchscreen. True, the display is just black and white, but at least you don’t need to drag a handheld out to the field with you. And it has a couple more features that fall under the “fancy” title for this sort of device.

The FLXA21 can measure the continuous sensor impedance, slope, asymmetric potential, and more. This wealth of data makes it possible to diagnose contamination, damage, burnout, and other issues to avoid unscheduled downtime in your process.

Plus, it has a quick setup guide to get you through the device configuration, which saves a lot of time and can apply to similar devices, if you’re just learning how to set up transmitters. It can also save the last five calibration results and estimate future maintenance and calibration time. Pretty good, huh?

Graphs FLXA21
Courtesy of Yokogawa

Last but not least, it has a feature called “trend graphics.” This feature can display up to 41 averages of your measurements to help you understand the behavior of your process and your sensor. The FLXA21 takes measurements every second, so you can see the maximum, minimum and average of these measurements. All in all, a decent little machine!

This video can tell you more about the FLXA21:

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