YSI History

The Story and Evolution of YSI...

In the beginning there were a few engineers and a lot of ideas.

The legacy of our global company reaches back to 1948 and a three-man partnership that was forged at Antioch College in Yellow Springs, Ohio, USA. This village, between Dayton and Columbus, still serves as the headquarters for what started as the "Yellow Springs Instrument Company" — now known as YSI Inc.

We invite you to browse our brief history and explore our timeline.


  • YSI founded in Yellow Springs, Ohio - The legacy of our global company reaches back to 1948 and a three-man partnership that was forged at Antioch College in Yellow Springs, Ohio, USA. This village, between Dayton and Columbus, still serves as the headquarters for what started as the Yellow Springs Instrument Company, now YSI Inc.


  • First quartz crystal electronic stopwatch
  • First practical medical electronic thermometer


  • First interchangeable thermistor temperature probes


  • First commercial heart-lung machine


  • First instantaneous blood-gas analyzer


  • First line of precision interchangeable thermistors


  • First practical dissolved oxygen meter for field and laboratory
  • European distribution network established


  • First linear thermistor temperature sensor
  • First polarographic biological oxygen monitor
  • Industrial Research magazine recognized 2 YSI products among the 100 most significant new technological products of the year: Model 53 Biological Oxygen Monitor - the first commercially available device for measuring oxygen uptake or evolution; and Thermilinear thermistor components - which first combined thermistor sensitivity with linear output


  • Design Analysis Associates, Inc. (DAA) founded by William I. Fletcher.


  • First immobilized-enzyme-activated polarographic sensor


  • First commercially successful whole blood glucose analyzer


  • First commercial gallium melting point temperature standard (29.7715°C)


  • First superior-stability precision interchangeable thermistor technology


  • First commercial alcohol measurement using immobilized enzyme electrode technology
  • First direct whole-blood L-lactate assays using immobilized enzyme electrode


  • Employee Stock Ownership Plan (ESOP) established upon retirement of Company founders.


  • Malte vonMatthiessen succeeded Hardy Trolander as president


  • First lab outside Germany accredited by the German Federal Bureau of Standards


  • Acquired Endeco, a Marion, MA, oceanographic data collection and monitoring company.


  • Acquired controlling interest of Clandon Scientific in England - This allowed for direct control of distribution in Europe and would later become YSI (UK) Ltd.


  • SonTek, a precision water velocity measurement company, founded in California
  • Released first environmental monitoring instrument, the YSI 6000, with patented Rapid-Pulse(TM), stirring-independent, dissolved oxygen sensor


  • First long-term in situ stirring-independent oxygen sensor
  • First stirring-independent microelectrode dissolved oxygen sensor
  • YSI achieves ISO 9001 certification


  • First chemically-wired fructose electrode
  • Named ESOP Company of the Year by the National ESOP Association


  • Achieved Fisher Scientific’s “Outstanding Quality Supplier” award


  • First glass-encapsulated precision thermistors manufactured using robotics
  • First conductivity instrument using Resistance Ratio Technology TM; used for high-accuracy measurement of ultrapure water.
  • Achieved Fisher Scientific’s “Outstanding Quality Supplier” award for the second year in a row
  • New $3 million state-of-the-art R&D facility opened


  • First reliable vented level technology developed
  • Achieved Fisher Scientific’s “Outstanding Quality Supplier” award a third year in a row
  • Recognized as one of the “Dayton 100” by Arthur Anderson
  • YSI (Japan) Limited established


  • First accurate commercial fiber-optic based CO2 measurement system
  • 'Who’s Minding the Planet?'® tag line adopted - motto expresses YSI's commitment to ecological sustainability.
  • Recognized as one of the “Dayton 100” by Arthur Anderson
  • YSI (Hong Kong) Limited established


  • Released BOD Analyst(TM), software that automates BOD testing.
  • Introduced SI 4800LC Thermistor Linearizing Circuit
  • Methanol chemistry added to the YSI 2700
  • First miniaturized chlorophyll probe integrated into a multiparameter system
  • Malte vonMatthiessen maintained CEO/Chairperson of the Board
  • Rick Omlor promoted to new role as President & COO
  • Acquired Victory Engineering Company, Springfield, NJ to complement YSI temperature product line.
  • Recognized as one of the “Dayton 100” by Arthur Anderson
  • Achieved ISO 14001 Certification


  • YSI 8500 CO2 Monitor released
  • YSI 556 MPS released
  • YSI 650 MDS released
  • Gayle Rominger promoted to Sr. Vice President
  • MCEO/Chairperson, Malte vonMatthiessen, appointed to Board of Ohio Biomedical Research and Technology Transfer Commission by Gov. Bob Taft.
  • Chosen as finalist for 'Enterprise Spirit Award' by Dayton (Ohio) Business Journal.
  • Lisa M. Abel, YSI’s Leader of Sustainability Strategies, chosen by Dayton (Ohio) Business Journal as one of its “40 Under 40” for leadership in her field.
  • Honored as charter member in U.S. EPA National Environmental Achievement Track (NEAT) program.
  • YSI chosen by Industry Week magazine as one of its 'Growing Companies 25'


  • Introduced YSI 600 QS Quick Sample (TM), a multiparameter spot sampling system
  • Introduced YSI 5200 Recirculating System Monitor
  • Introduced YSI 7100 Multiparameter Bioanalytical System (MBS)
  • Office opened in Qingdao, China
  • Acquired SonTek in San Diego, CA which expanded YSI's existing line of water quality monitoring products to include velocity and water quantity monitoring


  • Malte vonMatthiessen retired as CEO after 17 years and becomes Chair of the Board.
  • Rick Omlor promoted to President and CEO
  • Received Honorable Mention for the Innovative Process Award for cell culture, fermentation, and bioprocessing monitoring - sponsored by the Environmental Business Journal.


  • Ammonium and potassium measurement added to 7100 Multiparameter Bioanalytical System
  • Asian Hydroacoustics Center of Excellence in Shanghai opens
  • Opened office in Beijing
  • Opened Gulf Coast sales and service office in Baton Rouge, Louisiana
  • Acquires Hydrodata, UK
  • Received EN 12470 and EN 13485 certification and complies with EU In-Vitro Device Directive
  • Recognized as International Business of the Year by the Dayton (Ohio) Business Journal
  • SonTek/YSI's Argonaut-SW (Shallow Water) selected as Best New Agriculture Instrument by the Irrigation Association.


  • YSI Environmental, with partner Micro Molar Systems, LLC, developed a manufacturable microfluidic device.
  • YSI named as one of 25 of the fastest-growing companies in the region by the Dayton (Ohio) Business Journal
  • Sensors passed rigorous testing to achieve U.S. EPA's Environmental Technology Verification (ETV).
  • YSI twice named to Top 100 list by the Dayton (Ohio) Business Journal


  • Deborah Stottlemyer named the 2005 Chapter Officer of the Year by The ESOP Association.
  • YSI's second annual sustainability report recognized as Best Small & Medium Enterprise Report by the Ceres coalition and the Association of Chartered Certified Accountants.
  • YSI Temperature New Jersey facility closed
  • Former Victory Engineering product manufacturing transitioned to Ohio.
  • Nanotech/YSI, an environmental monitoring systems subsidiary in Japan, became 100% owned by YSI
  • Opened office in the Kingdom of Bahrain


  • YSI introduced wiped optical sensors for dissolved oxygen and blue-green algae
  • Gayle Rominger promoted to Executive Vice President
  • 'Good Corporate Citizen Award' from Yellow Springs, OH, Chamber of Commerce
  • YSI Temperature division sold to Measurement Specialties Inc.
  • Opened office in Ireland
  • Established 'Minding the Planet' grant through the YSI Foundation


  • YSI introduced the flagship model 'ProPlus' in the Professional Series, the new line of field and lab water sampling instruments
  • Acquired environmental business from AMJ Equipment Corp. Renames the new environmental monitoring and services company AMJ Environmental in St. Petersburg, Florida


  • Introduced EcoMapper AUV for high-resolution water quality and bathymetry maps.
  • Introduced 6-Series Anti-Fouling Kits for even longer deployment intervals
  • Introduced upgraded, multi-beam RiverSurveyor
  • Introduced xylose membrane for YSI 2700 biochemistry analyzer
  • Deborah Stottlemyer named the Ohio/Kentucky Chapter Employee Owner of the Year by The ESOP Association.
  • Rick Omlor recognized as regional winner of Entrepreneur of the Year/Technology Group by Ernst & Young.
  • Dr. Edward King joined YSI as CTO
  • YSI founder Hardy Trolander enshrined in the Engineering & Science Hall of Fame of the Engineers Club of Dayton (Ohio)
  • Product recycling program launched
  • Named to Top 100 Companies list by theDayton (Ohio) Business Journal
  • Honored with The State of Ohio's Governor's Award for Excellence in Exporting
  • Named Manufacturing Company of the Year by the Dayton (Ohio) Business Journal
  • Achieved MCERTS certification for multiparameter continuous water quality monitors from the Environment Agency of England and Wales


  • Opened office in Australia
  • Named ESOP Company of the Year by the Ohio/Kentucky Chapter of the National ESOP Association
  • Acquired Design Analysis Associates in Logan, UT -manufacturer of data loggers and radar level sensors
  • SonTek/YSI RiverSurveyor M9 named Most Innovative Product of the Year by the Marine Technology Society - San Diego chapter


  • Created Advanced Development Group (ADG) for design of new technologies and platforms
  • Received State of Ohio Third Frontier grant for nutrient sensor development
  • Named to Top 100 Companies list by the Dayton (Ohio) Business Journal
  • Introduced CastAway castable CTD instrument
  • Opened office in Abu Dhabi


  • YSI merges with Analytics division of ITT Corp. to form new water company Xylem.
  • Ron Geis appointed new General Manager of YSI; former CEO Rick Omlor continues as Executive Advisor.


  • EXO multiparameter water quality platform with multiple industry firsts and patents unveiled
  • YSI 2900 Biochemistry Analyzer introduced with intuitive graphic user interface and trusted measurement technology
  • IQ SensorNet wastewater process monitoring system introduced, enhancing YSI's wastewater capabilities


  • ProDSS (Digital Sampling System) portable multiparameter instrument, featuring smart sensor technology, becomes another exciting release in the Professional Series product line
  • EXO University On-Demand Sonde Training

A Brief History of YSI

Back in the late forties, two engineers, Hardy Trolander and John Benedict were joined by chemist David Jones and started looking for problems to solve through the application of good science. Shortly after the three men incorporated the company in 1948 and Hardy Trolander was appointed the first President, they were joined by David Case, another Antioch alumnus.

The four men worked with researchers at Fels Research Institute. Additionally, 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 at Wright Field, among them being principal inventor of the automatic radio compass still in use today.

The Air Force accepted the men's concept for a 16k random access memory (RAM) with on-board crystal clock in response to its need for a programmable timing device with precision and resolution well beyond anything available at the time. This successful prototype led to Air Force contracts that produced cash flow to support development and commercialization of further ideas.

First instruments released and sales grow

After a few years as a struggling start-up, YSI's first commercial instrument was designed -- the Model 3A Dielectric Constant meter which measured the stability of liquid suspension. Then followed interchangeable thermistor temperature probes, a notable industry first, and associated temperature instrumentation.


By 1960, YSI had several dozen employees and numerous instruments that had gained wide acceptance among scientists and researchers. A European distribution network was established early in this decade. The engineers continued to work hard to develop more innovative products.

Innovative sensor technology

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 oxygen electrode that allows dissolved oxygen to be measured in liquids. Applications not only include environmental ones, but biomedical and industrial as well.

For example, his invention enabled physicians to perform open-heart surgery because, for the first time, immediate blood oxygen measurements could be taken real-time in the operating room rather than having a sample drawn which then had to be taken to a lab for analysis. Dr. Clark also developed the technology behind the glucose biosensor, used daily by millions of people with diabetes and other conditions.

In 1970, Dr. Clark demonstrated the enzyme-activated polarographic measurement of glucose in water and pointed out that glucose could be measured in whole blood with the presence of the glucose oxidase enzyme. Within a couple of years, YSI was able to market its pioneering Model 23 Glucose Analyzer with a polarographic electrode.

At this point in time, YSI was building a range of instruments based on precision sensor technology for temperature and biomedical applications.

Hardy Trolander believed strongly in the social benefits of a business enterprise -- one that gave its employees meaningful work; one that contributed to the economic health of communities and intellectual stimulation of industries. This legacy was continued upon Hardy's retirement in 1983, with the appointment of Malte vonMatthiessen as YSI's second President/CEO. Malte focused on expanding our niche markets, initiated quality improvement programs, and developed alliances with domestic and global partners. During this time, sales and distribution were set up in the Eastern hemisphere.

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.

Innovation continues with upgraded R&D

Moving into the 1990s, the company adhered to a well-defined plan of providing quality products to specific global niche markets (environmental monitoring and testing, precision temperature measurement, and biotechnology) while continuing to reduce costs. YSI recognized its core competency in sensor technology and committed three million dollars for a new facility to house stepped-up sensor measurement technology teams.

Additionally, new product development and business processes incorporated environmentally responsible practices such as recycling, reduced-footprint packaging, and energy conservation.

During this decade, YSI introduced what became our most significant product line to date: the 6-Series environmental monitoring sondes. These instruments brought together YSI’s proven dissolved oxygen sensor with additional sensors into a family of products specific to monitoring water quality. Customers were able to leap out of the lab and into the field, where data was obtained more immediately and accurately.

Rick Omlor became YSI's third President/CEO in 2002. In 2005, Rick and his leadership team made the strategic decision to focus the business in a select few areas rather than following the 60-year history of ever broadened markets and sensor development. This strategy, focused mainly on the water quality and water velocity applications in the natural resource market, served the customer, company and shareholder very well.

In September 2011, in YSI’s 63rd year, ITT Corporation purchased YSI and, later that year ITT spun off its water-related businesses into a new publicly traded company, Xylem (XYL).

YSI, a Xylem brand, continues its legacy now with the backing of a 3 billion dollar company. It is part of Xylem Analytics, one of four divisions within Xylem where there are opportunities for expansion globally, sharing innovative technology across Xylem's brands but more importantly providing customers a more comprehensive solution to better meet their needs.

Xylem’s products enable its customers to sustainably transport, treat, test and efficiently use water in public utility, residential, commercial, agricultural and industrial settings, while Xylem Analytics is focused on field, portable, online and laboratory analytical instrumentation for applications in surface water, groundwater, coastal, aquaculture, wastewater and life science.

YSI will continue its legacy of invention and innovation as we move forward; and not just in the area of technology. We will continue to seek new creative solutions for remaining close to those who use our products and services, ways in which we operate our business, and methods for seeking and retaining talent.