Frequently Asked Questions and Maintenance Tips

What temperature compensation option does IC Controls recommend - PT100 or PT1000:

IC Controls recommends PT1000 (option -34) as it offers approximately 10 times better accuracy in most situations compared to PT100 (option -32).

 

pH or other liquid analysis sensors are often installed in humid environments with long signal lines, signal lead connections, and temperature fluctuations. PT100 changes 0.385 ohms per degree C; good clean signal lead connections often exhibit 0.2 ohms resistance to which 4 or 5 ohms resistance can be added from humidity resulting in about a 13 degree C temperature error.  This is even before considering the copper lead resistance change effect on temperature compensation accuracy. In contrast, the PT1000 changes at 3.85 ohms per degree C translating into a clean connection error of about 0.05% and reducing humidity/corrosion induced temperature error to about 1.3 degrees C.

 

When IC Controls sensors are connected to a non-IC Controls analyzer, we strongly recommend verifying whether the analyzer can be used with PT1000 temperature compensation in order to achieve the better TC accuracy.  If PT1000 is possible, option -34 should be specified in the IC Controls sensor.  Only in the event that PT1000 cannot be used should option -32 be specified recognizing that temperature compensation and measurement will be less accurate.

 

pH

 

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.”

 

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.

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 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.

 

How can I restore my old pH sensor that is slow, and gives a slope error (low span)?

If the pH response becomes sluggish and the slope of the probe starts to get too low, IC Controls Electrode Renew Solution can be used (P/N A1100092). The electrode renew solution will skim off a micro-layer of the coated glass, thereby exposing a new glass surface which will exhibit better pH response.

 

What is the Cause of pH Reference Contamination?

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.

 

How can I combat pH Reference Contamination?

To combat reference contamination, double junction and/or plasticized references are used to slow down the migration of the sulfide or cyanide to the reference wire. The second junction (IC Controls sensor option - 7) will to increase the path length of the contaminants to the reference wire. The longer the migration path, the longer it will take to reach the reference wire, extending the life of the reference. The second junction also forms a chamber which will slow the migration ions, again extending reference life. A second contamination deterrent is a plasticized reference solution (IC Controls sensor option - 8). The plasticized reference impedes ion migrates as a solid as opposed to a liquid. The more solid the reference solution, the longer contaminant migration will take thus protecting the silver/silver chloride wire.

 

How do I prevent clogging of my pH sensor in Pulp & Paper stock Applications?

Pulp fibers get caught in the area around the glass, clogging the electrode. Once clogged with pulp fibers the reference and glass to no longer have contact with the process, so pH measurements wander.  There are two different electrode modifications to help alleviate the clogging problem. One is a flat pH glass tip (IC Controls sensor option - 6). Benefits of Flat Glass: - reduces crevices to clog, - minimizes direct impact on glass. Disadvantages of Flat Glass; surface is parallel to flow so does not contact liquid sample as well, - glass has 90º angle which can break do to thermal stress. Another proven pH sensor design incorporates a domed pH glass in a pulp modified tip (IC Controls sensor option - 73), to ensure better contact with the solution while protecting the tip from the shearing action of the stock and clogging. Benefits of Pulp Modified: - Domed pH Glass stronger in thermal stress applications, - Tip Protected from shearing of dense stock, - De watering on the electrode edge for better pH response, - Flow over surface on domed glass provides more accurate pH results.

 

What is Caustic Ion Error in pH measurement?

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 minimize pH Caustic Ion Error?

- 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

 

How do I extend the life of my old pH sensor or Electrode?

You can soak it overnight in water with a pH of 2. Or you can use electrode renew solution (IC Controls P/N A1100092).   You may also refer to our maintenance tips presentation, listed on our website under service/support, maintenance tips #5: Extending the life of old sensors

 

How would I store my pH Sensor or Electrode when not in use?

Electrode storage solution is best (IC Controls P/N A1100090). Your next best option is 7 pH buffer (IC Controls P/N A1100018). You can use tap water but the pH glass and pH reference will continue to age as if in the process.

 

How do I know when to replace my pH sensor or electrode?

Do a speed of response test. If it takes over 3 minutes to receive accurate readings when going from 7 pH to 4 pH, then it is time to either clean or replace your sensor.

 

Why do I get slow and drifting readings from my new pH Sensor or Electrode?

Sluggish response is likely to occur when an electrode is taken out of long storage due to hydrolysis of the pH electrode glass membrane. The electrode is stored in salt water which is best for the reference, but is not hydrogen ion rich, as is best suited for the pH glass.

 

How can I speed up my new pH Sensor that is slow?

To revive or speed up the pH Sensor immerse it in a beaker of 4 pH buffer (lots of hydrogen ions) until the reading gets relatively close to pH 4. Rinse off the electrode and place it in pH 7 buffer until the reading gets relatively close to to pH 7. Keep alternating between 4 and 7 buffer until the response time is normal.

 

How do I clean my pH Sensors or Electrodes?

Method 1: Mechanical cleaning

On sludge, slime, or other soft deposits, mechanical cleaning can be used. Clean with a soft brush and a beaker or bucket of water. General debris and non-tenacious deposits can be removed in this way.  On hard scale, a standard flat screwdriver blade can be used to carefully scrape hard scale and other tenacious deposits off the reference junction. The IC Controls 642 open tip design also allows a screwdriver to carefully score and crack hard scale against the glass shaft, then carefully slide it up and off the pH glass tip without touching the pH glass.  After mechanical cleaning, again check the sensor against a pH buffer. If the sensor is still not developing the proper pH reading in the buffer you can proceed to a second cleaning method.

Method 2: Chemical cleaning

Chemical cleaning is a bit more involved, so IC Controls has made available a Chemical Cleaning Kit (IC Controls P/N A1600054). This kit contains all required supplies along with a complete instruction sheet to enable you to complete a chemical cleaning on your sensors.

 

How should I prepare my pH Sensor for use?

First inspect the sensor to make sure there is no damage. Then hold the sensor vertically and carefully remove the protective cap (typically black or red) from the sensor tip. Calibrate the sensor and place it in service.  IC Controls pH sensors are shipped with a protective cap containing pH electrode storage solution. The storage solution extends the life of the pH reference electrode during storage. If the sensor needs to be returned to stock, carefully replace the protective cap including the storage solution.  Check out our youtube video.

 

Chlorine

 

What is Chlorine?

Chlorine (symbol Cl) is a chemical element which can be found in the earth and the oceans. It is a greenish yellow gas at room temperature, and it is 2.5 times heavier than air. It turns to a liquid state at -34ºC (-29ºF), and it becomes a yellowish crystalline solid at -103ºC (-153ºF). Chlorine is highly chemically active and, as such, is typically found in nature bonded to other elements like sodium, potassium and magnesium.

 

Conductivity

 

What is Conductivity?

Electrical conductivity is a measure of the ability of a solution to carry a current. It is defined as the reciprocal or resistance, in ohms, of a 1 cm cube of liquid at a specified temperature which is expressed as siemens/cm. Current flow in liquids must be carried by ions. Ions are formed when a solid such as salt is dissolved in a liquid. For example, sodium chloride separates to form Na+ and Cl- ions. All ions present in the solutions contribute to the current that can flow through the sensor and therefore, contribute to the conductivity measurement. Electrical conductivity therefore is a measure of the concentration of ionizable solutes present in the sample.

 

What is a Conductivity Cell Constant?

Conductivity is measured by determining the amount of current that can be carried between two electrodes by a known amount of liquid. To determine the amount of current that will flow through a “known amount of liquid”, the volume between the two electrodes must be exact. This precise volume is known as the Cell Constant. The cell constant is a multiplier constant specific to a conductivity sensor. The measured current is multiplied by the cell constant to determine the electrical conductivity of the solution.  The cell constant, known as K, refers to a theoretical electrode consisting of two 1 cm square plates 1 cm apart. A cell constant has units of 1/cm (per centimeter), where the number refers to the ratio of the distance between the electrode plates to the surface area of the plate.

 

Dissolved Oxygen

 

What is Dissolved Oxygen?

Dissolved Oxygen (D.O.) is the amount of oxygen gas dissolved in a given quantity of solvent, usually water, at a given temperature and atmospheric pressure. It is usually expressed as a concentration in parts per million (ppm) or mg/L. For trace level of dissolved oxygen, parts per billion or µg/L is the unit typically used. D.O. The concentration can also be expressed as percent saturation, where saturation is the maximum amount of oxygen that can theoretically be dissolved in water at a given pressure and temperature.

 

Thermo Orion - Process Products

 

Are Thermo Orion 2100XP series monitors available with CSA certification?

Yes, Thermo Orion 2100XP series monitors are CSA and CE Certified.

 

MSDS Sheets

 

When should MSDS sheets be replaced?

Typically they should be replaced every 3 years. To be sure you have the most updated version, go to our website and check the date on the MSDS sheet under “preparation”. If there is a newer date, then replace your current version.

 

Are IC Controls MSDS sheets available in French?

Yes, many of our MSDS sheets are available for download in French. Go to our website as above and select the link with the description “French”. Please contact IC Controls if the MSDS you require is not on the website.

 

Maintenance Tips

 

Thank you for your interest in our Maintenance Tips!  We hope our tips help you get even longer life out of our product in your application. Simply e-mail 'sales@iccontrols.com' and they will be sent to you directly.

 

pH Sensor User Tips:

 

Tip #1:  Cleaning pH Sensors, part 1

Tip #2:  Cleaning pH Sensors, part 2

Tip #3:  Preventative Measures

Tip #4:  The Effects of Scale

Tip #5:  Extending the life of old sensors

Tip #6:  Like new reading from old pH sensors

 

Sodium Monitoring Tips:

 

Tip #1:  The Sodium Electrode

Tip #2:  The Reference Electrode

Tip #3:  The Sample Flow Effect