Product Review: Mettler Toledo M400 2-wire

Time for our next review! We’re checking out analytical transmitters this week. Frankly, I never had to work much with them. Maybe that makes me lucky. If any of y’all have worked with these things, then tell me about it.

We could really use more good overviews about these transmitters, though. Most vendors keep their websites clear as mud, so you’ll need to waste more time than you should to find answers. Some vendors have started improving the user experience on their websites and documentation, but not many. Let’s keep reminding them, shall we?

On this review, we have the first run for a new company on Visaya! The team of Mettler Toledo has joined us with the M400 2-wire transmitter. So let’s check out the features and see if this device can fit your process.

Grab a Red Bull (I’m drinking one now), have a read, and draw your conclusions!

M400 2-wire
Courtesy of Giphy

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 M400 2-wire looks like most analytical devices on the market. On one hand, that gives you a sense of familiarity; on the other, it doesn’t distinguish itself. For example, you can set up the device locally, but it doesn’t have a touchscreen. Of course, some touchscreens make you want to go back to the push buttons, but they’re getting better!

Anyway, it’s compact, at 144 x 144 x 116 millimeters, but heavier than other similar devices, around 1.50 kilograms. Not too bad, though. You can install it on a wall or pipe, but can you install it in your process? Hmmm. Let’s keep digging.

M400 2-wire
Courtesy of Mettler Toledo

Mettler Toledo calls the device a multi-parameter unit. That means it can measure pH/oxidation-reduction potential (ORP), oxygen, and conductivity. You can also connect analog or digital sensors to it. This can give you a chance to try out digital sensors, if you’ve never used them before, and explore the benefits of this technology.

Sadly, the M400 2-wire has a single channel to connect the sensors. Remember, though, that this device comes from the low end of Mettler Toledo’s portfolio. You’ll find some of the other models have more than three channels. If you want a fancier device, you should check those out instead.

What can it do?

The M400 2-wire has certifications for hazardous areas and more. You can find the approvals and certifications on the device’s datasheet. As a loop-powered device, you can send data and power through the same cables, which can save you money over a 4-wire device. Just a thought.

As far as digital protocol goes, you won’t find any news here. However, you can integrate it with HART, Foundation Fieldbus (FF), or PROFIBUS PA. Since those cover most plants out there, you should be okay.

And then we have the housing material, die-cast aluminum. And that’s it. Believe me, I checked for more but didn’t find any. Still, you have eight languages to choose from for your daily activities. At least someone thought about the users, if not the process environments.

Why should I care?

The M400 2-wire can do a good job reading sensor data from the field. It has a quick setup too, guiding you through the entire process smoothly. Not a new or fancy feature, but always welcome.

M400 2-wire
Courtesy of Mettler Toledo

The documentation says this device has Intelligent Sensor Management (ISM) to provide reliability, safety, and security. The ISM also comes with a list of features like dynamic lifetime indicator, time to maintenance, adaptive calibration time, and so on. It provides data on your transmitter and sensor conditions too. Most of the diagnostics will show up on the screen, and you can do a pressure compensation if necessary. For an entry-level model, it brings some pretty good bang for your buck.

It has no trend graphics on the display, though. I found this omission a bit disappointing, but maybe you don’t need it. Last but not least, accuracy and resolution. You’ll have to check out the datasheet according to your application and sensor. Make sure you check it against your specs.


Our new guest makes a pretty good showing in its debut, doesn’t it? It just may fit your process when you scale it out. If you disagree, by all means drop us a line down yonder and tell us why.

This video should give you more deets on the M400 2-wire:


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