The Evolution of Innovation: 75 Years and Counting

The Story of YSI from 1948 to 2023

YSI was founded on the spirit of innovation. The burning desire to solve a problem, develop a solution, and change the world is woven into the fabric of YSI and our team.

It all started in Yellow Springs, Ohio, in 1948. In the beginning, two engineers, Hardy Trolander and John Benedict, embraced their entrepreneurial side, setting out to solve the problems of the day through the application of good science. They were joined by chemist David Jones.

Hardy Trolander and Dave Case in 1954, doing what they loved—solving a problem.

With an investment of $100 each, the three friends began the Yellow Springs Instrument Company. Hardy was appointed the first president shortly after the founders incorporated the company. They were joined by David Case, another Antioch College alumnus (and tinkerer).

Together they collaborated with the Fels Research Institute at Antioch University on medical research. But, like many struggling start-ups, the team was willing to take on just about any project. Eventually, they bid on a job at the Wright-Patterson Air Force Base (formerly Wright Field) with the help of Fred Hooven, who became the fifth stockholder. Hooven had gained a reputation for his significant contributions to the Army Air Corps, among them being the principal inventor of the automatic radio compass, which is still used today.


YSI manufacturing in 1951.

Some of YSI’s first instruments included a camera timer, dielectric constant meter, telethermometer, and even an integrated radio for Huffy bikes.

Believe it or not, the Huffy radio bike was not the contract that put Yellow Springs Instrument Company on the map. Our founders’ big break was a contract for high-accuracy camera timers.

Trolander said of the early days, “There is an awful lot to be said for pigheadedness and for being too dumb to know what we should be doing. We weren’t so driven that we had to get a big return.”

The YSI radio on a Huffy bicycle in the mid-50s.

In the mid-1950s, joint research at the Fels Institute progressed and led to the development of YSI thermometers to measure core body temperature in sedated patients. This new instrument was developed for the healthcare industry, but the temperature readings were so stable and reproducible NASA pulled them off the shelf for use in outer space. And, in fact, in late 1955, the company’s first interchangeable thermistor temperature probes were used extensively in the U.S. space program.

Getting Started In Medicine

The history of YSI would be incomplete without mention of Dr. Leland Clark, to whom not only YSI, but the world, owes a debt of gratitude. Dr. Clark was a researcher at Fels with whom Hardy Trolander and the others worked closely. He is best known for having developed the aptly-named Clark polarographic oxygen electrode that allows dissolved oxygen measurement in liquids. Applications of this technology were endless and included environmental, biomedical, and industrial sensing.

Early on, Dr. Leland Clark and Hardy Trolander wrote an article that led to several developments and new instrumentation possibilities. This marked the beginning of several decades of collaboration on a wide range of medical devices. 

Dr. Leland Clark inspecting membranes and sensors.

Dr. Clark’s heart-lung machine paved the way for open heart surgery. He developed an electrode that could measure the oxygen in the blood and found a particular membrane that would allow these measurements to be consistent and reliable. YSI produced these electrodes in the first commercialized design.

This development led YSI employees (and the public) to realize the potential for dissolved oxygen measurement in other applications, such as environmental waters. Soon after, the area’s local utility, Dayton Power & Light Company, approached YSI with concerns about the discharge of thermal pollution into the nearby Miami River. The team didn’t know it then, but these initial conversations were YSI’s first step into environmental monitoring.

Who’s Minding the Planet?

YSI was minding the planet before the first Earth Day was held and before global climate change became a prominent issue. This environmentalist culture led to the development of highly precise water quality instrumentation—this continues today!

In 1963, YSI introduced the first commercial dissolved oxygen meter for the field and lab. Not long after, the company produced the first biological oxygen monitor and quickly became recognized worldwide as the leader in dissolved oxygen measurement and DO technology.


YSI commercialized the first dissolved oxygen meters utilizing the Clark polarographic membrane technology based on Dr. Leland Clark’s discovery, allowing us to become the leaders in DO measurement.

YSI didn’t become a household name in the environmental space overnight. Ray Schiff, who established the early distribution network for YSI instruments, reminisced, “We had to go overseas and set up similar supply houses and distribution to build our business. So, I bet $1,000 I could do it and set it up. I got a list of various countries, and I was able to set up distributorship in Europe by pounding the pavement.” Ray had no intention of losing his bet.

His work helped to equip environmental scientists around the globe with the most accurate sensors for their work, and many of the business partnerships he built and nurtured are still in effect today.

The Next Generation

During the 80’s, Hardy Trolander stepped aside and opened the doors for his successor, Malte von Matthiessen.

“When I came here, I discovered a high level of appreciation for what had happened before my arrival.” Von Matthiessen said, “What I did was simply build on Hardy’s successes.” At the time, YSI had three core businesses: temperature, life sciences, and environmental.

After several years with Malte at the helm, YSI began to sharpen its focus on product development and replaced the traditional hierarchical managerial structure with cross-functional and self-directed teams. He also established an Employee Stock Ownership Plan (ESOP), where all employees became owners of the company. His innovative leadership style helped define the organization for decades to come.


Supporting the next generation of scientific discovery and curiosity is important to YSI.

During Malte’s tenure at the company in the 80s and 90s, YSI:

  • Implemented a set of core company values to drive the business with a focus on ecological sustainability, employee ownership, community, and innovation
  • Established the YSI Foundation to support charitable and environmental causes
  • Adopted the ‘Who’s Minding the Planet?’ tagline to build the brand through a commitment to environmental stewardship
  • Acquired Endeco (now YSI Systems), allowing the company to enter the environmental monitoring markets for ocean and coastal applications
  • Opened the new state-of-the-art R&D facility along with offices in Japan, Hong Kong, China
  • Introduced the first ‘6-Series’ sonde, marking the beginning of a highly successful line of multiparameter, continuous water quality monitoring instruments
  • Introduced a multiparameter automated biochemistry analyzer
  • Introduced multiparameter recirculating system monitor for aquaculture
  • Acquired SonTek, adding water velocity and flow measurement capabilities to our sensing portfolio for water quality and quantity

Malta inspired a company culture of putting our customers first. Our employees bought into the concept—both literally and figuratively—as part owners of YSI. Over time, this culture manifested into a mindset of ‘how do we help solve customer’s biggest problems.’ As Ian Thompson, now Xylem Analytics Senior Sales Director, stated years ago, “A lot of our products are designed by customers. They tell us what they need, and we go to the drawing board and find a solution. By having customers design products, you could rest assured that your products are being used for good applications.”


We know that many of our customers are doing work that can change the world and, in fact, has.

A Focus on the Environment

After 17 years of dedication to YSI, Malte von Matthiessen retired as CEO, leaving the organization in the capable hands of Rick Omlor in 2002. It wasn’t long before Rick and his leadership team made the strategic decision to focus the business on a select few areas rather than following the company’s 60-year history of ever-broadened markets and sensor development. This strategy focused mainly on water quality and velocity applications in the natural resource market. It also led to many innovative products that YSI is best known for today in the environmental space.


Throughout the 2000s, efforts focused on the environmental side of our business, specifically water quality and quantity.

During Rick’s time as CEO in the 2000s, YSI: 

  • Expanded its international presence further, opening additional offices in Baton Rouge, Bahrain, Ireland, Spain, India, and Australia
  • Introduced optical sensors for dissolved oxygen and blue-green algae measurements, along with other new products such as membranes for xylose measurement in biofuels processing, an autonomous underwater vehicle for water quality mapping, and multiple-beam acoustic Doppler profilers
  • Released the first wiping system for water quality sondes, significantly extending instrument deployment times
  • Developed a vertical profiling system for high-resolution measurement of water quality throughout a water column
  • Achieved U.S. EPA’s Environmental Technology Verification (ETV) after rigorous testing of our instruments
  • Achieved MCERTS certification for multiparameter continuous water quality monitors from the Environment Agency of England and Wales
  • RiverSurveyor M9 was named Most Innovative Product of the Year by the Marine Technology Society
  • Received Third Frontier Grant for the development of new sensor technology from the State of Ohio

Joining the Xylem Family

In September 2011, ITT Corporation purchased YSI. Later that year, it spun off its water-related businesses into a new publicly traded company, Xylem (XYL).

YSI, a Xylem brand, continues its legacy of minding the planet—now with the backing of a $7 billion company (2022 revenue). Since the acquisition, YSI has benefited from new opportunities for global expansion and the sharing of innovative technology across Xylem’s sister brands. But more importantly, we can now provide our customers a more comprehensive solution to better meet their needs.


YSI, a Xylem brand, can now leverage a much broader portfolio of water resource solutions to solve water-related issues, including quality, transport, treatment, and dewatering.

In the 2010s and early 2020s, YSI:

  • Released the EXO multiparameter water quality platform in 2012. Packed with multiple industry firsts, it quickly became the standard for long-term water quality monitoring
  • Introduced the IQ SensorNet wastewater process monitoring system in 2012, enhancing YSI’s wastewater capabilities
  • Combining the sensor technology from EXO with the portability of the Professional Series, YSI developed the ProDSS (launched in 2014) for use in a variety of environmental applications
  • Launched the HYCAT Autonomous Surface Vehicle (ASV) in 2018. It features an unsinkable catamaran hull and can carry a suite of instruments—YSI EXO2s, SonTek HydroSurveyor M9, and Side Scan sonar—never before offered in a single system!
  • The 3017M Chlorine Analyzer—released in 2020—is a DPD colorimetric analyzer that continuously measures free or total chlorine in municipal drinking water and wastewater applications using an EPA-approved method
  • Released in 2020 after several years of development, the EXO NitraLED is the world’s most accessible UV Nitrate sensor. Built with state-of-the-art LED technology, the NitraLED simplifies and reduces the cost of unattended nitrate monitoring for point and non-point source pollution in freshwater environments
  • Another innovative product was released in 2020—the SonTek RS5! As the world’s most compact and robust ADCP for collecting river, stream, and canal discharge data, the RS5 is small yet incredibly powerful
  • Continuing our development of the EXO platform, YSI released compact, batteryless versions of our sondes in December 2021 (EXO1s, EXO2s, and EXO3s) that are ideal for integrated systems where power is supplied as well as specialized applications such as attachment to an AUV or aerial drone, integration with a buoy, or horizontal profiling where lightweight is optimal
  • A major update to Hydrosphere was completed in 2022. This is a scalable, collaborative data visualization software platform for outdoor water monitoring
  • Launched in 2022, our Kor Mobile app for our EXO sondes allows users to view live and recorded data, calibrate sensors, set up unattended deployments, and ensure equipment operates at peak performance
  • A complete update of our free EXO University on-demand training program was completed in 2023, providing fresh, detailed, and practical guidance on how to set up, calibrate, maintain, store, and troubleshoot an EXO sonde

A Promising Future

YSI will continue its legacy of innovation as we move forward, and not just with technology. We will continue to seek creative solutions to support those who use our products and services, in how we operate our business, and in the methods for seeking and retaining talent to continue the mission of our founders. We’ll keep looking for problems to solve through applying good science.


We are fully committed to minding the planet and supporting our amazing customers worldwide who do it daily.

Looking back on his years with YSI, Trolander said, “I think I am proudest of how we treated our people and that when I left the company, 80% of what we made had never been seen until YSI made it.”

While Malte opined, “People, people, people. It’s what I cared most about and what I missed the most when I stepped down from the company.”

Rick Omlor celebrated his time with YSI, recalling, “YSI strived to do something good for the environment. I was drawn to it because it’s a bunch of smart people doing great work. And that’s what got me up in the morning.”

It’s what gets all of our employees up in the morning. We’re proud to be a part of a 75-year legacy of scientific innovation.

‘Who’s Minding the Planet?’ Yep. That’s YSI.

2 Responses to this article

I've been very pleased to work with YSI over the years. Ever since my first purchase of the old YSI temp profile system we used on a gov site for doing temp profiles in a trout stream in the northern part of new your state. To working on developing the 600YSI sonde for doing profiling in monitoring wells all over the country. The one time our group visited YSI at Yellow Springs inst. we were very interested in your systems. I am retired now, but worked for DOD and corp GE.


¡Felicidades en sus 75 años de aniversario!


Add a comment

Your comment will appear after it is reviewed.

By clicking on Submit you agree that Xylem may use your personal data to aid in providing you support, and may contact you directly on this matter. Please have a look at our Privacy and Cookie Policy for more information on how/why and where we use your data