If you need a new flow meter, maybe the QuadraTherm 780i from Sierra Instruments can help you!

As you know, we here at Visaya have reviewed a bunch of flow meters by this point; you can see those on the product review pages or search for the models on the site. But we haven’t discussed many thermal mass flow meters, a device growing in popularity. Not many vendors offer this solution, but this type of meter can fit in multiple applications as a cheaper choice to the standard options.

Sierra Instruments brings a lot of experience applying flow meters worldwide, so let’s jump in the features world and see how we can deploy this model!

Disclaimer: This product review examines only features, not performance. If you’ve used this device, feel free to share your experience in the comments. This content serves the purpose of providing information if you want a new device.

What is it?

First off, let’s start with our usual notes – first impressions and how it looks.  The 780i’s housing resembles 90 percent of the devices on the market, and the vortex flow meters from Sierra also have the same design.

You have the option to get a local display and local setup. The ultrabright LCD screen indicates pressure, flow rate, totalized mass, and engineering units. The local setup has six push buttons and a pretty simple interface. Through it, you can change units, set alarms, Dial-A-Gas, and more.

But as an inline flow meter, it needs process connections like flanges, and you’ll need to cut the pipe to install it. If you want an insertion-style meter, then skip the 780i and go to the 640i.

What can it do?

The QuadraTherm 780i has flow and temperature measurement as standard, with pressure optional. Plus you can apply it to measure all non-condensing clean gases and inert gases.

Before we go further, you should know the limitations of this technology. You can read our article “Thermal mass flow meters- what you need to know” to learn more.

The QuadraTherm 780i can fit pipes from one inch to eight and has a flow range from 0 to 60,000 surface feet per minute. Besides that, you can use it in gas or ambient temperatures from -40 to 200 degrees Celsius.

As a four-wire device, you get power supply and communication in different cables. The 780i works with 100 to 240 volts of alternating current or 24 volts of direct.

Additionally, you can get the signal through RS 232 or one of three analog connections, flow, temperature, and the optional pressure. You can get the alarm output through a contact switch or solid-state relay as another option. And if you pick the VTP version in your order, then you get an additional pressure sensor up to 5000 psia.

Why should I care?

The 780i has good integration options -HART, FOUNDATION Fieldbus, Modbus RTU, and PROFIBUS DP. So I’m sure you can find one for your application. It also has approvals and certifications for several requirements.

Want more? Because it has more! It has the Drysense sensor to eliminate drift, which brings excellent benefits for your application. Check out the video at the end of the article to see what I mean. And it has a shorter inlet and outlet run than other options on the market, because of the flow conditioning already built into the sensor body.

Last but not least, you have a Boiler-MACT-certified device for area source boilers and significant source boilers plus a lifetime sensor warranty. It sounds good, right?


In general, we have an outstanding thermal mass flow meter in the QuadraTherm 780i. It has a bunch of possibilities and features that can fit in many applications. However, as always, you should take a look at other options. You can find good stuff there as well, and they might suit you better. Do your research, folks!

This video explains the Drysense technology. To know more about flow meters, you can get in touch with our engineers and we will be happy to help.


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