DO202 2-Wire Dissolved Oxygen Analyzer (DISCONTINUED)

Notice: This product was discontinued on Apr 30, 2015. See this replacement product:

Flexibility, reliability and low maintenance are among the benefits provided by the EXA DO202 Dissolved Oxygen 2-wire transmitter. Designed to meet the exacting requirements of Dissolved Oxygen analysis in the modern industrial environment, it contains many features to ensure the best precision whatever the application.

DO202 is housed in a rugged IP65 enclosure and is a loop powered 2-wire transmitter to combine safe and simple wiring, installation and commissioning with the advanced functionality of the YOKOGAWA EXA microprocessor analyzer family.

The DO202 is a SMART transmitter. Digital communication is done either through HART® protocol superimposed on the 4- 20 mA current or completely digital through Fieldbus communication: Fieldbus Foundation. This SMART functionality allows the transmission of up to four process variables, information stored in the logbook, diagnostic data and remote configuration of the analyzer.

Yokogawa has developed drivers for PC configuration and maintenance software for different platforms like PRM, AMS and Pactware. The DO202 transmitter is a universal Dissolved Oxygen Transmitter that accepts both galvanic sensors like DO30 and Polarographic sensors like OXYGOLD and OXYFERM. It is suitable for both ppm Pharmacuetical applications as well as ppb applications for Power Generation.

  • Universal input accepts Galvanic and Polarographic sensors and various temperature compensating elements (Pt1000, 22k NTC)
  • HART® communication standard with 4-20 mA loop powered model
  • Fieldbus models for Fieldbus Foundation
  • Wide measuring range including ppb, ppm and % saturation
  • Certification for hazardous area pending (ATEX, FM, CSA)
  • Recommended sensors model DO30(G) , PB30, OXYFERM, OXYGOLD (for ppb measurement)
Application Note

When used to measure the dissolved oxygen in an aeration tank, sensors tend to quickly become contaminated and need frequent cleaning. A cost-effective solution to this problem has finally been found with the development of the Yokogawa DO402 Dissolved Oxygen Converter system. 


Most zinc are produced at hydrometallurgically, where a high-grade zinc product can be obtained and valuable metals mixed in the raw material can be recovered. In the hydrometallurgy, the raw material of zinc concentrate is roasted and then dissolved in sulfuric acid to remove impurities. The process called leaching and pH control of the leachate is important.

Industry:Chemical, Power


Background Information

The core of the activated sludge process is primarily dependent on the control of the aeration basin. The most essential component of any activated sludge plant is the biomass, anaerobic and aerobic bacteria, that attaches themselves to the waste, and digest the waste resulting in relatively clean water as the by-product.

There are several types of bugs that are responsible for different duties. There are the carbon eaters (carbonaceous) and chemical eaters like ammonia (nitrogenous). Just like any other living organism they need certain conditions in order to sustain life and reproduce.



Many components in a process must be in balance in order to obtain complete synergy; example biomass blends, air, return activated sludge (RAS), waste activated sludge (WAS) and throughput. The aeration basin is a holding and/or treatment pond that everything cycles through. It is essential to monitor and control several factors that can influence the efficiency of the biological conditions in the basin; for example:

Temperature: Normally the temperature will be between 10- 40°C. Most biomass bugs achieve optimum efficiency in this range. Increasing or decreasing the temperature can result in the increasing or decreasing the rate at which the bugs eat and reproduce. Along with this all chemical reactions that are taking place at the same time are affected by the process temperature as well.

pH: For most systems the pH should be kept between 6.5 to 8.5 pH, when the pH is too high or too low, the biomass losses the ability to convert the food to energy and raw materials. A pH below 6.5 may cause the growth of fungi and fungal bulking, and will have to be adjusted using a caustic, lime or magnesium hydroxide.

Low Nutrients: If nitrogen and phosphorus are not presented in sufficient amount it can limit the growth rate of the biomass. A sign of nutrient deficiency includes foam on the aeration basin.

Dissolved Oxygen: DO is one of the most critical points of measurement; for most processes the target concentration will be between 1-3 mg/L. The concentration amount is an indication of the basin environment; whether it is in denitrification (excess nitrate, NO3) or nitrification (excess ammonium, NH4) environment. Essentially the DO measurement is set to a level to minimize the ammonium breakthrough. It is not uncommon to see NH4 and DO measurements together.

The DO measurement should be maintained at the point of greatest oxygen demand in the system. Normally this is near the intake portion of the aeration basin, because when the process is in the secondary clarifier no oxygen is added and the biomass bugs are starved of oxygen. When the process is returned to the aeration basin via the RAS pumps the biomass is returned to an oxygen rich area and the bug consume vast amounts of oxygen right away.

Septicity/Toxicity: Septic wastes contain elevated amounts of sulfides and organic acids (such as acetic acid).Other organic materials and heavy metals are also toxic to the biomass, reducing their efficiency or even destroying them.



Having too much oxygen in the process is not a problem for the biological system; however the cost for generating the oxygen is one of the largest expenses. By obtaining a good representative average of the dissolved oxygen present in the basin could save the plant large amounts of money. For this reason multiple measurements points are sometimes put into place.

Application Note


Two types of polymerization reaction are used to produce styrene-butadiene copolymers, the emulsion type and the solution type. This section addresses volatile organic compound (VOC) emissions from the manufacture of copolymers of styrene and butadiene made by emulsion polymerization processes. The emulsion products can be sold in either a granular solid form, known as crumb, or in a liquid form, known as latex.

Copolymers of styrene and butadiene can be made with properties ranging from those of a rubbery material to those of a very resilient plastic. Copolymers containing less than 45 weight percent styrene are known as styrene-butadiene rubber (SBR). As the styrene content is increased over
45 weight percent, the product becomes increasingly more plastic.

As shown in below figure, fresh styrene and butadiene are piped separately to the manufacturing plant from the storage area. Polymerization of styrene and butadiene proceeds continuously through a train of reactors, with a residence time in each reactor of approximately 1 hour. The reaction product formed in the emulsion phase of the reaction mixture is a milky white emulsion called latex. The overall polymerization reaction ordinarily is not carried out beyond a 60 percent conversion of monomers to polymer, because the reaction rate falls off considerably beyond this point and product quality begins to deteriorate.


Because recovery of the unreacted monomers and their subsequent purification are essential to economical operation, unreacted butadiene and styrene from the emulsion crumb polymerization process normally are recovered. The latex emulsion is introduced to flash tanks where, using vacuum flashing, the unreacted butadiene is removed. The butadiene is then compressed, condensed, and pumped back to the tank farm storage area for subsequent reuse. The condenser tail gases and
 noncondensables pass through a butadiene adsorber/desorber unit, where more butadiene is recovered.

Some noncondensables and VOC vapors pass to the atmosphere or, at some plants, to a flare system. The latex stream from the butadiene recovery area is then sent to the styrene recovery process, usually taking place in perforated plate steam stripping columns. From the styrene stripper, the latex is stored in blend tanks.

From this point in the manufacturing process, latex is processed continuously. The latex is pumped from the blend tanks to coagulation vessels, where dilute sulfuric acid (H2SO4 of pH 4 to 4.5) and sodium chloride solution are added. The acid and brine mixture causes the emulsion to break, releasing the styrene-butadiene copolymer as crumb product. The coagulation vessels are open to the atmosphere.
Leaving the coagulation process, the crumb and brine acid slurry is separated by screens into solid and liquid. The crumb product is processed in rotary presses that squeeze out most of the entrained water. The liquid (brine/acid) from the screening area and the rotary presses is cycled to the coagulation area for reuse.

Typical Process Details:

crumb2Fluid: Crumb slurry

  1. Fluid composition (normal):
    Water: 95% wt

    Polymer: 4.06% wt

    Fatty acid: 0.2% wt

    Extender oil: 0% wt. (Max. 1.45% wt)
    Rosin acid: 0.078%wt
  2. Acidity (min/orm/Max): 0.0/3.6/14.0
  3. Fluid design conditions P@T: 1.033 Kg/cm2- 
g@115 degC
  4. Boiling point @ operating pressure: 100 degC 

    Dew point @ operating pressure: 100 degC
    Boiling point @ atmospheric pressure: 100 degC

    Dew point @ atmospheric pressure: 100 degC
  5. Density: 980 kg/m3 (Norm)
  6. Fluid able to foul

Max. pressure: 1.033 kgf/cme-g Tempe: 62 degC

Crumb rinsing and dewatering

Typical Problems:

This is indeed a tough application. The rubber tends to stick on the holder. The rubber does not tend to stick on the glass very much.


To mount the holders in such a way that they can swing with the process flow and make them easy to remove for manual cleaning: 0.5 or 1 m immersion fittings hanging on the hoisting cable on a hook.


  • Sensor: SC25V series
  • Features SC25V
  • External titanium Liquid Earth
  • Pt1000 integration in pH compartment giving highly accurate temperature compensation
  • CIP and Steam cleaning possible
Large internal KCl volume giving the sensor a longer life time
  • SC25V-ALP25 for chemically harsh applications and high temperatures

Alternatively, SENCOM sensor can be used. (SC25F)

Sensor Holder:

The FD20-P37 comes with hoisting cable made of SS316. When the holder is mounted this way, just hangs in the vessel, then it can swing with the flow. Otherwise the rubber slurry may damage the sensor if the holder is mounted rigidly. Most probably the sensor protection cage must be removed to prevent the polymer to fill the cage.

Application Note


an1Diazonium Coupling (Diazo Coupling, Azo Coupling):

Due to their positive charge, diazonium cations, which are generated by treatment of aromatic amines with nitrous acid and a stronger mineral acid, may participate in an electrophilic aromatic substitution as an electrophile. The electrophilic reaction center is the terminal nitrogen of the - N=N group. As a result, two aromatic compounds are coupled by a -N=Ngroup. This is known as the azo group (diazo group).

The corresponding reaction is called diazonium coupling (diazo coupling, azo coupling). However, the electrophilicity of diazonium ions is only relatively weak, as their positive charge is delocalized.an2 The unsubstituted benzenediazonium cation may react only with strongly activated aromatic compounds, such as phenolates and amines.

Azo coupling is the most widely used industrial reaction in the production of dyes, lakes and pigments. Aromatic diazonium ions acts as electrophiles in coupling reactions with activated aromatics such as anilines or phenols.

The substitution normally occurs at the para position, except when this position is already occupied, in which case ortho position is favoured. The pH of solution is quite important; it must be mildly acidic or neutral, since no reaction takes place if the pH is too low.


Application Information

Typical process details:

  • Chemical Composition - Coupler + Diazo Coupler – 48 % caustic + Nepthol + Water Diazo -36% HCL + Diecloro Anelene + Water Operating Temperature – 55°C
  • Operating Pressure – 4 kg/cm2

Typical problems:

Limited life of sensor


The process is indeed quite aggressive so Glass is best material.

Sensor Selection:

Sensor Option #1: SC21C-AGC55 would be best, if it is possible to pressurize the electrolyte to 5 bar (72PSI).

Features for type SC21C-AGC55

  • Heavy duty pH sensitive glass.
  • Flowing reference system for pollution resistance, 
and highly stable reference potential.
  • Use in combination with the presurisable electrolyte 
reservoir to obtain a positive flow towards the process (K1500YA)

Sensor Option #2: SC24V is possible if the cation (salt) content is stable during the pH control step.


The SC24V is a differential pH sensor. This means that the reference is not a (liquid) junction but a glass sensor which does not respond to pH changes (within the applicable range of the sensor). Therefore the sensor is truly maintenance free and the output voltage of the sensor depends only on the salt concentration of the process.

The sensor responds to pH changes rather than analyses the accurate pH value. In that sense it is best to describe the sensor as pH control sensor rather than pH measuring sensor. 
A pH sensor measures the voltage that the pH membrane measures as function of the pH value of the process sample. This voltage is then compared with the mV output of a reference cell that is independent on the pH value of the sensor.

In most pH control applications the salt concentration is rather constant, so the output of the SC24V differential sensor is only dependent on the pH of the process. 
A rule of thumb is that a change in salt concentration of +/- 25% has an effect of less than 0.1pH on the pH reading.

Application Note

Fish perform all their bodily functions in water. Because fish are totally dependent upon water to breathe, feed and grow, excrete wastes, maintain a salt balance, and reproduce, understanding the physical and chemical qualities of water is critical to successful aquaculture. To a great extent water determines the success or failure of an aquaculture operation.


In stable dispersion of fine particles is the pre-requisite for the selective flocculation technique involving separation of ultra-fine valuable particles from the gangue. Among mineral processing techniques selective flocculation technique is known to have outstanding potential of capturing the particles of particular mineral in slurry of mixed mineral system by selective adsorption of water soluble polymers known as flocculants.


Pigment producer manufacture produces pigments to supply to paints, plastics, inks, construction, textile and cosmetics manufacturers etc. The pigments come under wide range - general purpose grades, high performance, and specialist hard-to make colours and effect pigments.

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