Thermal flow meters

Here we are again, and today we have some prime candidates! Both sides have a tradition in manufacturing thermal flow meters. The FCI ST100 comes from Fluid Components International, and Fox Thermal Instruments gives us the FT2A.

Let’s dig in! You know the drill: take a seat, have a read, and draw your conclusions!


We’ll start from the beginning, when you first see each thermal flow meter. Yes, the visual effect can relate to the user experience, so let’s have a look!

When you meet the ST100, you could say, “Okay, it’s a cool device. Nice color, good display.” However, you can’t tell anything about setting up the device just from looking at it. You’ll need to work it out or get the salesman to tell you.

Thermal flow meters
Courtesy of FOX Thermal – Courtesy of FCI

The FT2A, on the other hand, surprised me. It doesn’t have an attractive design and could stand to make a better first impression. But it has a simpler display than the ST100, and you can tell how to set it up from the push buttons on the device. Good deal, Fox.


Both thermal flow meters offer a wide range of protocols, although they tackle this factor very differently.

The ST100 has the traditional options, providing a genuinely seamless integration. HART, Foundation Fieldbus, PROFIBUS PA, Modbus RS485, analog communication – the gang’s all here!

Courtesy of FCI

On the other hand, the ST100 uses its ethernet protocol only for setup. They only need to take a short step forward to launch the first thermal meter on Profinet or EtherNet-IP! Come on, FCI!

Meanwhile, the FT2A offers similar options, but with a few gaps. While it provides DeviceNet and PROFIBUS-DP, it leaves out Foundation Fieldbus, PROFIBUS-PA, and the basic HART. I kinda miss those guys. Fox does provide a device with HART communication, the model FT3, if you need it.

Conversely, the FT2A gives you a protocol based on ethernet communication, the Modbus TCP-IP. Very on trend. However, the integration is, shall we say, less than seamless? Frankly, I had to wonder how I’d connect this transmitter to my control system. Kinda evens out.

Flow elements

The ST100 comes in three flavors of flow element and different materials. Basically, your choice depends on your application. The ST100 uses  FPC, FP, and S sensors.

Fortunately for us, the FCI crew included a table of gas conditions and characteristics in the brochure. Research made easy!

Thermal flow meters
Courtesy of FOX Thermal

The FT2A comes with PowerPro Sensor technology. It took me a minute to figure out the benefits of this kind of sensor, but I found ’em. Fox claims that this tech will give you a better low flow, low end sensitivity, and high accuracy. Let’s hope they’re right!

Also, you have different materials for your flow element, but you can’t tell which to pick. Mr. Internet to the rescue!

Fox created an online tool, the Fox flow meter configurator, to analyze your process data and offer the best flow meter for you. Yeah, we like that.

Gas and gas mixes

Super-important bit here, so pay attention.

If you don’t see your gas or gas mix listed, then you probably can’t use the thermal flow meters, but ask first, because you never know. FCIs provide a huge list, though, so the chance of you not finding yours will be slim.

On the Fox website, if you select the product, you have a nice comparison among the three models. However, when you start digging into the gas and gas mixes, the first flow meter has all of them listed, but the FT2A and FT3 don’t. There you’ll find “extensive.” Kinda vague.

I spent a couple minutes trying to find the type of gas supported, but you don’t have this information in the documentation. On the plus side, the online tool has the gas list and makes it clear what the flow meter can support. That’s better.

General information and documentation

Nowadays, when you have a question or want to learn more about a device before you buy, you’re gonna look online. The instrumentation world hasn’t caught all the way up yet, but it will soon. With that in mind,  companies need to think more about their website experiences, like how easily a viewer can find an answer.

The FCI website felt pretty good. It went with a traditional design, but you could find what you wanted. I particularly liked the brochure PDF, where you have all the important details on the devices.

Thermal flow meters
Courtesy of FOX Thermal – Courtesy of FCI

Fox did equally as well with its site. The product comparison and online tool can help a lot with vetting flow meters. Still, they could improve the interface a little, keep everything on the same page without the need to slide up and down.

Fox falls short on the documentation, though. Some of the info is missing or hard to find, like an explanation for the PowerPro Sensor. More please, Fox.

Fancy points

Few of these features qualify as deal breakers or deal makers. These are more about preference than anything that’ll make a real difference. But as always, your mileage may vary.

ST100 brings cool options like USB ports and Ethernet communication, which will help with your setup. It also has an micro-SD card to record  process information that can store approximately 21 million readings. Sweeeet.

Thermal ST100
Courtesy of FCI

Personally, I consider the display the coolest part of the fancy things. You have all information available on your screen, and the color is amazing! The setup doesn’t seem quite as user-friendly, but I can live with that.

On the other side, the FT2A has fewer fancy features. Nonetheless, you can still find the USB and Ethernet communication and protocols like DeviceNet and BACnet MS/TP.

Fox thermal mass flow meter
Courtesy of FOX Thermal

Funnily enough, I really like the simplicity of this meter. I also like the company’s long history on the market. These two bits win points with me, for sure! If it ain’t broke, don’t fix it, am I right?


You can’t go wrong with either of these thermal flow meters – unless of course, neither of them suit your application at all. So check your protocol options, the size of your pipe, the accuracy you need, and the weight of your wallet before clicking the Buy Now button!

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