642 Industrial pH Sensor – TOP SELLER

pH sensors with porous reference junctions allow KCl to migrate through the junction into the process to complete the electrochemical connection. Since the junction is porous, some aggressive processes can also migrate ions into the reference, causing contamination and premature failure. As the process migrates into the reference it may attack the silver/silver chloride wire, changing its chemistry which results in the electrode drifting. This is seen as an offset away from zero mV during calibration. There are a number of different constituents that can contaminate the reference electrode. Two major contaminates in the industrial market are sulfide (S2-) and cyanide (CN-). Sulfide is commonly found in kraft pulp and paper mills, mines and oil refineries. All of the different liquors in the kraft process have a high sulfide content and therefore, the pulp stock will have a significant amount of sulfide as well. Cyanide, is typically found in mines, metal refineries, and electroplating. The cyanide is for metal separation in flotation cells. Thus, contamination of the reference is an issue for both pH and ORP sensors which are used in these processes.

– In applications normally above pH 10, use High pH glass (IC Controls sensor option -3)
– Wash the sensor in acid to refresh it (IC Controls P/N A1100091)
– If sensor becomes very sluggish, use pH sensor renew solution (IC Controls P/N A1100092) to replenish pH glass surface

A caustic (sodium) ion error occurs when the concentration of hydrogen ions is low (when pH is high). As the pH goes up, the concentration of hydrogen ion goes down, at the same time the concentration of sodium ion will increase. Sodium is very close to hydrogen in its chemical structure. As the concentration of hydrogen ions decrease, the glass will start to recognize sodium as hydrogen, giving a false and therefor lower pH reading.

How can we prevent coating of the pH Glass?
Coating of the glass causes poor contact between the glass itself and the process. Good contact by the electrode is essential for quick, accurate response in the process. Thus, to help keep the glass clean and responsive, there are a couple of techniques that can be used.  IC Controls sensors are designed with two flutes to allow self cleaning. By turning the flutes to 75°, the process does not directly hit the glass which will slow down the coating action. Therefore, there is no mechanical cleaning which increases reliability and reduces maintenance. Insert the electrode with the flutes at 75° to flow. By inserting the probe at this angle a vortex will be created around the glass. The vortex will increase the velocity of the process around the glass and reference which will, in return, hasten electrode response time and keep the reference and glass cleaner. This approach is particularly beneficial where sharp, fines material can wear away any lime buildup.

Advantages:
– No Mechanical Parts to Fail
– Longer Sensor Life
– Less Maintenance
– Better pH Response

In application where the flow is stagnant, or not linear, or the coating is soft, a chemical spray cleaner can be attached to the tip of the pH sensor. Mounting the spray cleaner on the tip allows timed intervals of automatic cleaning without operator handling or maintenance. Spray cleaning also allows choice of the best chemical for cleaning the pH sensor and improving response.

Advantages:
– Reduced Operator Handling
– Longer Sensor Life
– Less Maintenance
– Better pH Response

How can you clear a scale coated pH Sensor?
In the past, a hydrochloric acid (HCl) solution was used to remove scale form the tip of the electrode. Although this has been somewhat effective, IC Controls’ gentle scale remover, P/N A1100094, will better clean the electrode. You can also try using liquid detergent to remove minor coatings.

Why does IC Controls use Silver/Silver Chloride pH Reference Electrodes?
The silver/silver chloride (or Ag/AgCl) reference has advantages for use in the industrial pH market. First, the temperature stability is good in applications ranging up to 105ºC (220ºF). Plus, with stabilizers added, accurate pH measurements can be taken to temperatures in excess of 125ºC (260ºF). The silver/silver chloride reference has become an IC Controls standard.

Why not use Calomel vs. Silver/Silver Chloride Reference?
Like the glass electrode there are also different types of reference electrodes that can be utilized in any given pH measurement. The two common references are the calomel electrode and the silver/silver chloride reference. The Calomel electrode is not used in industrial applications because the electrode breaks down when the temperature exceeds 80ºC or 175ºF. It is also part mercury, which is a health hazard.

How Do Glass pH Electrodes Work?
The glass electrode basically consists of four major components, a glass membrane, an internal buffer solution, a reference wire and the glass stem.  The pH glass electrode works with two reference electrodes, a reference inside the glass and a reference that is in contact with the solution outside of the glass. pH measures the milli-volt difference in the pH electrode system. A leached layer forms on both sides of the pH glass membrane. The difference in potential between the inner and outer layers is called the phase boundary potential and is the potential milli-volt difference that is the pH signal.  For best results, a symmetrical liquid cell is set up on both sides of the glass membrane. To set up the symmetrical cell, the internal fill solution in the glass and the reference fill solution are similar in their makeup. The symmetry is important so that the temperature curves for the two solutions are close, thereby canceling each others temperature effect.

How Do pH Reference Electrodes Work?
Reference electrodes work like a battery with the chemical components producing a predictable millivoltage, that is also in electrical contact with the solution being measured. The reference is a constant millivoltage thus, giving the glass a reference point to distinguish changes in Hydrogen ion concentration seen as a potential across the leached layers.

Learn more about pH sensors:

• Blog – Importance of Accurate pH Monitoring and Control
• Blog – pH Sensor Life in Harsh Applications
• Technical Articles – pH Sensor in Metallurgical Applications
• Technical Articles – How Electrode Design Correlates with Optimum Performance in pH Measurement
• Technical Articles – High Purity pH Measurement
• Technical Articles – The Right pH Electrode for Steam Cycle Monitoring and Control
• Technical Articles – Reliable pH Measurement in Oily Applications
• Technical Articles – Modern Sustainable Cyanide Destruction

View pH sensor mounting options –  Insertion, Submersion or Ball-valve retractable 

What is pH?  The everyday answer:
pH is a short form for the power (p) of Hydrogen (H), which is a way of expressing the measurement of the hydrogen ion concentration. The pH scale is the way to express how acidic or basic a solution is. The pH scale is 0-14, where a pH of 0 to 6 (or 6.9) is a acidic, 7 (or +/- 0.9 around 7) is neutral, and a pH above 8 (or 7.1) to 14 is basic or alkali. Because ions come in massive numbers the measurements are made using logarithms, so pH 7 is neutral, pH 6 has 10 times more Hydrogen (H), pH 5 has 100 times more Hydrogen (H) than 7, . . . until pH 0 has 10,000,000 times more Hydrogen (H) than 7.

What is pH? The Chemists expanded answer:
A pH sensor will measure the activity of the hydrogen ion. Since the activity of the hydrogen ion is nearly identical to the concentration of the hydrogen ion, the practical definition is p[H] = -log[H+]. The concentration of hydrogen ion typically lies between 10E-14 and 10E0 mol/L. It is therefore convenient to express hydrogen ion concentration using the pH scale where p becomes an operator which says: “take the base 10 logarithm and multiply by -1.”