Differential pH/ORP Sensors

The cation differential pH and ORP sensors were designed for difficult applications where conventional sensors are ineffective. These include measurements such as brine solutions to applications as diverse as electrolysis processes and cheese manufacturing.

The problems experienced in these applications most often relate to the reference cell and are the result of either:

  • high diffusion potentials at the reference junction
  • high temperatures (often encountered in applications such as in chlorinated brine processes)
  • and high ground-loop currents.

Yokogawa’s cation differential sensors feature a sealed glass reference and do not have a liquid junction nor any electrolyte to come in contact with the process. Therefore, the sensors do not suffer from diffusion potentials or fouling, which ensures measurement stability while being virtually maintenance free. There are different versions of differential pH sensors available and the significance of the advantages they have to offer over a traditional electrode is appreciated only after regularly using a conventional reference electrode in these difficult applications.


The FU20-FTS is the newest development in pH sensor technology available from Yokogawa. This sensor combines the measuring technology of our 12 mm differential sensor and the ruggedness of the appreciated wide body FU20 design in one product.

As is common in the market, Yokogawa uses silver/silver chloride reference cells in its products. In a wide range of applications, this solution has proven very effective and remains a cost-effective solution.

The lifetime of the conventional sensors is highly dependent on regularly maintaining pH equipment. Frequent cleaning is required to eliminate reference poisoning. 70-80% of industrial users will fully benefit from using differential sensor technology in their high temperature and pressure applications.


  • No junction
  • No open connection from the process to the inside of the sensor
  • No possibility of poisoning reference element
  • No use of diaphragm hence no issues of plugging or coating of the junction diaphragm
  • No outflow of electrolyte so no depletion issues



Measurement Theory Cation Reference
pH Range 2-14
ORP Range -1500 to 1500 mV
Temperature Range 0 to 105°C (14 to 221°F)
Pressure Range

0 to 10 bar (0 to 145 PSIG) @ 25°C

0 to 5 bar (0 to 72 PSIG) @ 105°C



Notas de Aplicación
Descripción General:

Continuous technology improvement is ongoing in the pulp & paper industry to obtain the best possible performance. Problems at the wet end (stock preparation) can rarely be corrected downstream. That is why monitoring and controlling pH in pulp stock is critical to the paper making process. Essentially, at every stage in the manufacture of paper, correct pH values play a vital role.

Notas de Aplicación
255 KB
Descripción General:

Current trend for increasing mercury awareness throughout the public sector has caused the government to take action. Recently, the Environmental Protection Agency (EPA) has focused their efforts on controlling mercury levels produced in various coal fired power plants. Based on information from several case studies, the EPA developed the Mercury and Air Toxics Standards to cut back mercury emissions. The most popular technology utilized by coal plants to meet the new standards is a scrubber which cleans the off gas from the combustion process. ORP sensors can further monitor the effluent from these scrubbers to ensure optimal mercury emission levels are achieved. By closely monitoring the mercury concentrations in the effluent, plant managers will be able to easily confirm their plants are meeting the EPA's standards.



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