6 pH transmitters you must know


6 pH transmitters you must know

Yep, time for another list! We reviewed a couple of pH transmitters last week that you’ll see again in a moment, and we wanted to pop in a few others for you to consider as well. But before we get started, I have a question. Does your accuracy depend on your transmitter? What do you think?

For example, let’s say you see pH 7.21 on your display. The transmitter rounds the last digit up or down, so at best you have a margin of error around +/-0.01. The specs for all the pH meters I’ve ever seen state +/-0.01 or 0.02, so we won’t use accuracy as a parameter. Granted, anyone with experience in pH measurement knows that the transmitter’s rounding is the least of your worries. Buffer solutions, pH electrodes, and even users can all reduce accuracy more than that. But we can come back to this topic in another article.

The basics and beyond

The humble pH transmitter can have many names – meter, converter,  instrument, device, etc. Regardless of what you call it, it should show you the pH value of the product you want to measure by converting the millivolt signal from your electrode into a pH value. It must also let you adjust and calibrate the electrode.

Of course, you probably want more than just values and adjustments. What about compensating for temperature? Handling buffers from more than one vendor? Analog or digital electrodes?

And you want a signal you can send to your computer system to control your process, usually an analog signal proportional to the measured value. A digital protocol can send much more data besides measurements, like sensor identity, status, and so on. 

You’ll probably install it on a wall or pipe, so can you do that easily, or will you spend hours with the manual figuring out where to connect the cables? Can you read the display from a distance? If it shows an error, then can you understand what it says? Sounds simple, but you may be surprised.

The following list covers most of the above as standard, which makes these devices good choices for most applications. Now let’s dive into 6 pH transmitters you must know!


Courtesy of ABB

This traditional 2-wire meter has a standard display with no backlight, along with a keypad near the display. The manual doesn’t say much about different installation possibilities, but it looks like you can install it on a wall. You have to order separate accessories if you intend to install it on a pipe.

The TB82 measures pH with an accuracy of +/-0.01 pH and 1 degree Celsius, which sounds optimistic. It only accepts analog sensors, but it’s the only entry on this list that you can use for ion-selective measurement. You can order a version for hazardous areas, and it comes with certificates for CSA, FM, and ATEX. So it covers most applications outside of Russia and Japan!

The TB82 also has sensor diagnostics for glass and reference impedance, but the manual makes configuration difficult. For output signals and protocols, it offers analog, HART, FOUNDATION Fieldbus (FF), and PROFIBUS PA.

Seems like an okay device for conventional analog electrodes, although the manual could use some clarity and the gentle hand of a graphic designer.

You can find out more about ABB’s TB82 here.

Endress+Hauser Liquiline M CM42

Courtesy of Endress+Hauser

This 2-wire single-channel device reads for pH, conductivity, or oxygen using Endress+Hauser’s Memnosens sensors. The display doesn’t have a backlight or other illumination, but it gives messages in clear text. You can choose between 14 languages, so this one can talk to a lot of people in the world. The scroll-wheel makes it particularly user-friendly.  Installation for a wall looks easy, but you’ll need accessories for pipe or panel installations.

Only the non-explosive version provides multi-parameter functionality, but you can use it for hazardous areas, and it has certificates for ATEX, IECEx, FM,CSA, NEPSI, EAC, and TIIS. You can get analog, FF, and PROFIBUS PA, but you’ll need the digital protocol for diagnostics.

Endress+Hauser has more on its CM42 here.

KNICK Stratos Pro

Courtesy of Knick

This 2-wire transmitter works for analog and digital sensors. By exchanging the input card, you can switch between pH, dissolved oxygen, or conductivity. It also has a 2-channel input card available except for Zone 1. In fact, it won’t support digital sensors in Zone 1 either. It comes certified for ATEX/IECEx/FM/CSA Zone 2/Cl 1 Div 2, GOST, and NEPSI.

The device has an IP67 housing and a nice color display, although you’ll need the manual to translate abbreviations on the display. It also has wall and panel mounts as standard, with optional assemblies for a pipe mount.

The Stratos Pro provides communication over one analog output, with the second output as optional. It also offers HART, FF, and PROFIBUS PA. Diagnostics check glass and reference impedance, and the manual is easy to read with clear installation instructions. The segmented display with the abbreviations is still a minus, though.

Learn more about Knick’s Stratos Pro here.

Mettler Toledo M400 2-wire

Courtesy of Mettler Toledo

This multi-parameter transmitter can use analog or ISM digital sensors for pH, conductivity, oxygen, or carbon dioxide. You’ll find the illuminated display easy to read and messages in clear text. Its IP66 housing will install on a wall or in a panel. You can use it in hazardous areas, and it has certificates for NEPSI, ATEX/IECEx Zone 1, and cFMus Cl1 Div1. 

On the down side, this loop-powered device only has analog, FF, and PROFIBUS PA available, and it only uses ISM digital sensors. Also, the manual contains a lot of text and is not easy to read.

Check out more details on the Mettler Toledo M400 2-wire here.

WTW IQ Sensor Net DIQ/S 181

Courtesy of WTW

This single channel multi-parameter device is a little different from the others. For starters, it only communicates with WTW IQ Sensor Net sensors and only works for wastewater. The backlit display has multiple languages and clear messages, making it pretty user-friendly.

It can measure pH, oxygen, conductivity, or turbidity, depending on the WTW sensor you connect. It also limits you to non-explosive areas, so if you have volatile wastewater, then you’ll need a different device.

It has two analog outputs and three relays but only one diagnostic, for glass breakage. On the other hand, it seems easy to install the device on a wall or a pipe. The manual is understandable, always a plus. 

Read more about WTW’s IQ Sensor Net DIQ/S 181 here.

Yokogawa FLXA21

Courtesy of Yokogawa

This 2-wire 2-channel converter works for pH, conductivity, or oxygen. You can use analog sensors or Yokogawa´s digital SENCON pH electrodes. Because it’s not a multi-parameter device, you need to specify your parameters or else change the input modules later. And although it claims to have two channels, you only have one output. Still, the touch display has clear text and 12 different languages.

If you choose the 2-channel input card, then you can program it to set off an alarm if the measurements between the channels go beyond a preset value. You can use it in hazardous areas, and it has certificates for ATEX, FM, CSA, IECEx, and NEPSI.

For communication, the FLXA 21 has analog, HART, FF, and PROFIBUS PA available. The touch display looks quite cool and will likely make configuration more user-friendly.  Sadly, the second measuring signal won’t go analog, and the device only supports SENCON digital sensors.

Yokogawa has more on the FLXA21 here.


What features do you want? Do you fancy a color touchscreen, multiple protocols, or voice command? Tell us in the comments!

Related tags: ABB DIQ/S 181 Endress+Hauser FLXA21 Knick International M400 2-wire Mettler Toledo ph measurement pH transmitters Stratos Pro TB82 TB82pH WTW Yokogawa
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