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Analytical Measurement

Video: 
Tuesday, March 30, 2010 - 10:00am

Topics Covered:

  • pH/Conductivity
  • Basic pH Measurement Theory
  • What is pH?
  • Types of pH electrodes - the measuring electrode and the reference electrode
  • Affects of temperature on pH
  • How to calibrate a pH loop - automatic and manual calibration techniques
  • Troubleshooting
  • pH applications - where to use them?
  • Conductivity Basic Measurement Theory
  • Conductivity Applications
  • Conductivity Sensor Technologies
  • Calibration techniques

What You Will Learn:

You will learn the theory and practices of pH, the operational definition of pH, the various electrode cells required for accurately measuring and making a pH measurement. You will also be taught the cleaning and calibration techniques and troubleshooting. We will also review applications and analyzers. Additionally, we will discuss the basic measurement of conductivity, applications, units of operation and different sensor technologies.

Who Should Attend:  Any Industrial customers who use analytical equipment such as:

  • Power Companies
  • Chemical
  • Pharmaceutical
  • Refining

Jennifer:

Hello everyone and welcome to the webinar. My name is Jennifer and I am the marketing assistant for Industrial Controls. Today's webinar is analytical measurement. The presentation will take about forty-five minutes and after the presentation we will take some time to answer your questions. During the presentation, free to enter your questions into the chat interface on the right-hand side of your screen. We will also open it up to voice questions where you can raise your hand but this option is only for people with phone connections and not those using their computer microphones. Now we are going to hear from our panelists.

Joe has been with Industrial Controls for 7 years. He is currently the Regional Sales VP and responsible for Industrial Instrumentation development.  Prior to joining Industrial Controls, Joe has 30 years experience with Process Instrumentation including sales, application engineering and also field service engineering.

Our second panelist is Tony and he is a Territory Manager, working for Honeywell out of the Cincinnati office. Tony has practical experience and coal-fired and nuclear power plants, chemical plants, water and wastewater market customers, petrochemical applications and industrial wastewater. At this time, I will pass the presentation to Joe.

Joe:

Good morning everyone and thank you for attending the analytical measurement seminar. I want to give you a quick background on Industrial Controls in a relationship with Honeywell. We have been in the industry for 34 years, since 1976 and we have been in partnership with Honeywell since 1991 so we have been working with Honeywell in their field teams for the past 19 years. We are Honeywell's largest distributor and we as a company have 17 regional offices. We represent Honeywell in 11 locations and cover 14 states and we have 128 sales and support professionals throughout the organization that are available to help you with questions and applications, quotations, setting up field sales meetings, etc. so I'm going to pass this over to Tony who has been with Honeywell and he will be presenting the product. Again, as Jennifer said, if you have any questions during the session type something in the chat button and we will give you some ample time at the end of the presentation, thank you.

Tony:

Good morning and my name is Tony and like Joe said I am with Honeywell. The presentation today is on analytical instruments and Jennifer was right. The presentation will last about forty-five minutes and we already have one technical issue. Jennifer, I'm frozen, hold on just one second. See if that works. I cannot move my screen, Joe.

Jennifer:

Okay Tony, we are actually going to host it from my screen so if you just give me one minute and we will bring it up.

Tony:

Thank you, for some reason I am not able to advance slides.

Joe:

This is Joe again. I just jumped on. I'm going to give you a quick infomercial on our company profile I would say it is coming back up in a minute but again with all of these different offices we get involved with both industrial and commercial process instrumentation. We deal with HVAC controls, combustion controls, industrial valves, all types of industrial components and factory automation. We also do a lot of technical training but it is in-house as well as now webinars through our new website says you haven't had an opportunity I am offering you to look at our website, www.industrailcontrolsonline.com. It is very interactive. We have direct links to all the different manufacturers that we represent. So it looks like we're up and running again. Tony, do you have access now to the slides?

Tony:

Yes, I sure do. Alright, let's go to the next slide Jennifer. The products that we are going to discuss all covered on this sheet. The top line, over on the left, is our analyzer. We will talk about that a little later on. I want to talk immediately about the products in the middle under conductivity when we get to that section. The picture in the center are toroidal conductivities and the one down kind of in the center of the screen is what we refer to as clean water, pure water conductivity cells and you will see the difference between those later. So going to the next slide, we are going to cover on the pH slide what is pH, the difference between acid and base or alkalinity and the acid side, and what the pH scale was. You can read these but the biggest difference, the biggest conversation that we're going to have is what a measuring and what a reference electrode does and how they function. We are going to talk about calibration of pH, maintenance and troubleshooting. Then under conductivity, we will spend a shorter amount of time because it is basically an easier subject. We are going to talk about the definition, the unit of measure, again, how to calibrate and the difference between cell constant.

Okay, so the basic theory of pH, next slide. Basically pH is 0 to 14 and the reason it is 0 to 14- really when you are measuring pH you are measuring the hydrogen ion activity. If the hydrogen ion concentration in a solution is less than the hydroxyl ions, you are always talking about it being on the acid side. If the solution is- go ahead to the next slide. If the hydrogen ion is greater than the hydroxyl ion, then we are always talking about it being acid. The greater the hydroxyl ions, the more basic, the more hydrogen ions, the more acid and what dictates whether it's more hydrogen or hydroxyl ions is really what you were doing with that solution. But that is where the 0 to 14 comes in, 7 neutral, 14 highly caustic, 0, highly acid. On your pH of common solutions, go ahead and hit it two more times, whoever has got control, on the process side or values for common substances. I will give you an example, your blood sugar or your blood measurement is about 7 pH and so is milk. I have kidded people if you're buffering a pH system and you don't have anything around 7, you can use milk because it is about 7. If you get down into your soft drinks, that will range anywhere from high 2’s to up around 5 for root beer. If you are a beer drinker, then mid-fours, orange juice around 3 so you can see that just and every day, almost everything that we eat is on the acid side. Salad dressing case the way it does because it is on the acid side. On the process side, you will see that things like ammonia nitrate that has got about the same pH value as beer. Vinegar has about the same pH value as bleaching would be so pH is in our lives every day. Notice that if you have ever got acid indigestion, which would be less than 7, things that you would take for it to neutralize your stomach and who use the word neutralization in process applications too but you might use something like in anti-acid like milk of magnesia in your stomach which has got about a 10.5 to help neutralize your stomach acid if you have acid indigestion. It is in our lives every day.

If you measure pH, you basically use two components, the reference electrode and the measuring electrode. Even in what they call combination electrodes today, that combination electrode will be broken down into two sections and three sections. It will have a reference electrode, it will have a measuring electrode and it will have a temperature compensator. So what are the functions of a reference electrode? One is to produce a stable reference voltage and the other is to produce a low resistance current path. We produce a stable reference voltage by using an Ag/AgCl element in the same electrolyte as what is in the glass electrode. We produce a low resistance current path by keeping your liquid junction clean and the reference electrode, about 90% of the measuring electrodes that are in the field today use potassium chloride but there are other agents that can be used. Go ahead and hit the next slide. You can use potassium chloride that is in the 3 to 4.3 molar areas because it gives you good mobility. You can use slurry which also has still good mobility. If you think about potassium chloride or reference solution, which you want it to do is migrate. You wanted to migrate out of the reference electrode and into the solution. So you are looking for something that has good mobility. In our industrial probes, we use a gel potassium chloride because it's as good viscosities and its mobility while good enough to make the measurement is in a gel form so that it is slow to migrate into the system.

There are some solid-state electrodes out that capture the salt without immobilizing it. There are basically 2 types of references that I want to talk about. One is the top picture and the other the bottom. The one on the top is a small industrial reference electrode. In these cases, they have a finite amount of potassium chloride in them. They are filled when they are shipped from the plant with potassium chloride or a reference solution. The reference electrode acts as a referee. It is attempting to supply a constant millivolt signal back to electronics. The salt in it and we will cover this in later slides but the salt in there is needed to make contact with the process and also to make contact with the measuring electrode. In the industrial type, we use gel filled. Again, the reason for that is it is harder to contaminate it. It is slower to migrate. We don't need as much reference electrode in industrial probes as we do in ultra pure for water manufacture or for ultra pure in a power plant. When we are talking about the ultra pure which is the electrode on the bottom we like to use the flowing type and in that case it is a 1 molar type KCl and we will talk about that also later on. There are industrial types for process and it is good to know that you basically use two different reference solutions for two different applications.

If we break the electrode down, again, whether you are using two electrodes or a combination of electrodes you always have a measuring electrode and a reference. The reference is on the left-hand side and in that reference is an Ag/AgCl wire that is there in the center with the little ball on the end. That basically goes back and ties into your electronics. It is immersed in potassium chloride and the job of the potassium chloride is to migrate through the liquid junction and into the solution. It is supplying really what is referred to as salt bridge. You are basically wanting the salts to leave the reference electrode, mix with the solution, and touched the reference electrode therefore it is like a battery therefore finishing the bridge. In both cases, the body, coming down on either side is structurally strong but on the glass electrode, the glass on the very end is very thin and is not only glass but actually has, let’s call it a membrane on it, with some oxides because glass being an insulator would have a hard time if not impossible generating millivolt transfer through it to go up in that wire. With the membrane on the end of that glass is very fragile. I have seen people use corduroy pants or a knife or sandpaper to get dirt off of them. Not only are you cleaning them, but you are also damaging that membrane. It is important to know here that the reference electrode is trying to maintain a constant potential, constant millivoltage while the glass is developing the differences based on the hydrogen and hydroxyl ion activity in that solution.

So here is your glass electrode. Again, there is typically a seven buffer on the inside of the glass. It has got pH sensitive glass on the end and again membrane. Typically you can see this weld line where the bottom is attached to the structural body glass on the side. What is important with this slide is to see that millivoltage generated by the glass electrode at 25°C and we have rounded these numbers off but it is basically 59 mV per pH change. So you get a positive millivoltage, + 59 at 6 pH and -59 mV at an 8 pH and as you can read 118, 177 as you change pH values. Those are always true that 25°C. It is important here to know, we'll talk about buffers later on, but buffers all have the same situation. If it is a 4 buffer, that is 4 or 4.1 or 4.2, whatever the side of the bottle says, at 25°C.

We will get to that millivoltage a little later on for some additional conversation. We have mentioned up to this point, glass electrodes, it is also important to note that Honeywell has available and understand there are a few other of these products on the market, a non-glass pH probe. Honeywell calls them Durafets. It is FET technology. At the end is a field effect transistor and it is a state-of-the-art technology, non-glass and again it is used in applications, almost every application, except hot caustic, high purity water and as we get into the high purity conversation you will see why you wouldn't use it a Durafet in hydrofluoric acid. Hydrofluoric acid will etch the FET just like it would etch glass. Again, glass electrodes are fragile. They will do all the applications except hot caustic and hydrofluoric acid. Hot caustic also and we are talking about 12 pH at 180° or hotter will also etch glass.

The measuring electrode which is sensitive to hydrogen ions develops a potential voltage directly related to the hydrogen ion concentration. The reference electrode contains a fill solution which slowly reaches out into the electrode and through the reference to junction. They fill solution makes contact with the solution in the measuring electrode completing the circuit. Thus, the voltage between the reference electrode should maintain at a constant voltage in the measuring electrode will change proportionally. What is important here is to know that if pH is not working well many times, I'm going to say 80% of the time, the problem is the reference electrode. The reason for the in an industrial probe is one you could be running out of potassium chloride. Number two you could be contaminating that potassium chloride and number three you could block the liquid junction. Some people call it a frit. You can block that and keep the potassium chloride from leaching out into the system.

We talked about temperature before. It is important here to see that if we go down the middle of the column you see basically the same thing that was on those other slides. Zero millivolts at 7 pH and 59 mV in either direction as it moves up to 6 or down or up to 8. Better temperature changes, let's say it goes up to 50°C, 7 stays constant but your 6 will generate 64 mV instead of 59. 5 pH will generate 128 instead of 118 and that is strictly a function of temperature. Some people think that temperature compensation compensates for this difference and it really does not. The temperature compensation in any pH probe simply takes the Nernst equation. The Nernst equation, part of it has a temperature in the equation so it is kind of a variable constant if you will end the temperature compensation just tells you that at that pH and that temperature your pH is correct.

Your temperature compensation does not compensate for chemistry changes in the solution. It only compensates for changes in the glass electrode slope. It does not compensate and this is what I was talking about just a second ago. It is not compensate back to 25°C. It compensates only for nernstian effect. Let's talk about calibration. A lot of people know how to calibrate a pH probe. You normally take it out of a process, you will stick it in a 4 buffer, you clean it, you stick it in a 7 buffer or an 8 buffer or 10 buffers, whatever buffers you are going to use. What you are doing at that point really is I am going to say reestablishing a zero. If you are using an industrial probe and you contingently use this potassium chloride that is in the reference, that reference electrode is changing potentials the whole time you are losing electrolyte. So what you do when you recalibrate if you take into effect the age of the measuring electrode and the amount of potassium chloride and the age of the reference and you re-zero it so that it is reading correctly. So you will stick it in a 4 buffer, makes the instrument read 4, clean it DI water, a 7 buffer if you can't find DI water and then stick it in your second buffer. Those buffers should be about 2 pH different. The other way that you can calibrate and I like this, especially in applications where taking out the electrode is difficult or a major change in temperature if the electrodes are hot is to do a grab sample. Walk over with your lab and a beaker, go to the process, and pull a sample. There are techniques in doing this correctly and we can always talk about that at some other point. We don't have enough time today but grab a sample using the proper techniques. Read what the pH of the process is with your lab and simply make your analyzer read exactly what lab unit is doing. You can use either the standard solutions or grab samples.

So calibration of pH measuring instruments is necessary because similar electrodes may produce slightly different potentials in the same solution and a corrective adjustment is needed at the measuring instrument. Also electrode output will change over a period of time, again, the lack of potassium chloride in an industrial probe which makes periodic calibration necessary. The calibration intervals, everybody asks how often do we recalibrate these things. That is really based on operating experience or whatever your company mandate is but basically you recalibrate at intervals to eliminate drift and make sure your pH measurement is good. Many times I have seen people take a grab sample, use a lab and if the pH is right on or close enough, they don't even recalibrate at that time.

We have spent a lot of time talking about industrial probes. I would also like to talk about high purity measurements. These measurements are typically used in power plants but I have also seen where chemical plants making DI water or other applications where the conductivity is less than 10 microsemiens where people would use high purity pH measurements. In a power plant, why is pH measured. At this point it is because you want to control corrosion. Why are you measuring pH of dissolved oxygen, conductivity and ORP and others is you are trying control the corrosion that is happening in the tubes and other parts of your plant and of course for proper water treatment. The challenge in ultra pure water is the low ionic sample. If we are talking about DI water, which is deionized water, there is very little to help a pH electrode. In an industrial probe, you have got plenty of help in the solution, in the beaker you have got other contaminants if you will that helps a salt bridge get created from the reference to the measuring. In ultra pure water, the challenges low ionic sample and again let's go back to power plants. You do everything you can to get that down to H2O with maybe a little bit of ammonia in it what you are talking about low ionic samples.

The challenge of measuring pH in pure water is your reference junction potentials. Again, we talked about that in the industrial probe. You don't want to see differences in the potentials and a reference electrode and the reason that you don't want that is because you don't want it to look like its drifting or giving you incorrect readings. Streaming potentials can also happen in low ionic samples. Streaming potentials are generally caused by using ultra pure water in some sort of plastic tubing or plastic monitoring system. I used the word scraping, the water just scraping past this plastic can cause static charges which will affect the potentials being developed at the glass and measuring electrode and therefore can cause errors in pH. That's the reason that we always recommend that a grounding rod the use in the sample. And of course contamination from air in-leakage and I see that quite a bit if the flow sample is not high enough. If you are down around 25 or 50 cc, you could actually cause some CO2 leakage from the exit side of the chamber to come back up in to contaminate the sample.

The reference junction, a low resistance at the liquid junction is critical for a stable pH reading. At high purity water, the electrolyte solution can actually be washed away leading to a high resistance at the liquid junction. This will again create the pH reading and make it look like it's unstable. We use a flowing reference junction, we will show that in the next slide, that will help the pH stay stable by continuing to submit and provide an adequate amount of potassium chloride to reach out into the chamber. We also use the solution ground to eliminate that stream and potential that we were talking about before.

So Honeywell has devised an ultra pure system that uses a reference electrode first in the measuring electrode second. We have a sample inlet on the left and a sample outlet on the right and remake it with a 3/16 stainless steel bowl. The middle portion of those three elements on top is a temperature electrode and your counter electrode, your ground for reducing electrical noise. We make the reference electrode first because it is a flowing reference as you'll see in one of the next slides. It provides the potassium chloride. The sample inlet is a very small hole so it is actually injected into the chamber at an angle so that it swirls and picks up the potassium chloride necessary to make the measurement.

The flow rate on the Honeywell system audit be someplace between 50 and 500 cc per minute. It is good to break at this point and tell you that Honeywell also has this not only for pH but also for ORP applications. The flow rate should be between 50 and 500. I have seen about 250 cc be an optimum measurement. Again, swirl the sample so that take, we actually contaminate the sample if you will, with the salts because it is low ionic. It is very clean so therefore to help that salt bridge to be developed between the measuring and reference electrode we not only use a flowing reference but we swirl it so that we get a nice uniform pattern. If you haven't seen it before, this is the Honeywell product showing a direct line. Again, the bottom and the top left is the canister or holder of the potassium chloride. The reference electrode is on the left. The measuring electrode is on the right.

One of the other things that power plants need to correct for and won't go into this in major depth is that in your analyzer you ought to be able to select not only the measurement of pure water but a AVT curve or a phosphate curve or an oxygenated treatment curve. I will add correction to the measurement based on the chemistry that you're using in a plant. Some people call the solution temperature coefficient and it is available in the Honeywell analyzer.

So the pH measurement used electrodes and temperature compensations. It also uses preamplifiers. The preamplifiers basically are used to change the high impedance signal of a glass electrode into low impedance. It is also there to reduce noise. So the purpose of the glass electrode preamplifier is to transfer high impedance to a low and to be a signal conditioner. In an industrial application, if you're using ISFET or a Durafet, it is simply a signal conditioner. The ISFET does not provide a high impedance signal so you don't need to convert that. The preamplifiers can either be internal to the sensor in some competitive products or the preamplifier can be remote or it can be internal to the analyzer. We don't like putting the preamp in the sensor because the sensor ultimately is going to go bad and we don't feel at Honeywell that you need to replace the sensor in the preamp every time you replace the sensor. Once amplified, your pH signal can go very long distances up to several thousand feet if necessary. We won't spend a lot of time here but the preamplifier can look in different configurations. The one on the right is the preamplifier cap adapter used in Durafets. The one on the left is a typical preamplifier that can be used in glass electrodes. There are a number to choose from.

We are running a little bit behind therefore I'm going to pop through these next slides fairly quickly. Instead of a preamp, Honeywell has a direct line transmitter, 24 V transmitter that you can use to also attach to a pH probe and send it a long distance being a 4-20 signal it can go great distances. That direct line can be attached directly to pH probes or on the next slide as you can see you can use remote pH probe and a wire to get it back to the direct lines so that you can send it again back as far as you need to send it. These can be used for glass or Durafet pH probes. The Durafet, again quickly, is completely different from glass. It doesn't work exactly the same way. You've got a source, a gate and a drain and a pH sensitive ceramic coating on the bottom of it. It will take a wide temperature range from basically freezing to boiling. It is difficult to break. It is very fast responding. You have got quick disconnect cables. You can also replace the reference junction, the frit. If that gets contaminated or dirty it can be replaced and also if you want to, it can be refilled with potassium chloride. The other great thing about it is it can go up to 50 feet without a necessary preamplifier. Let's just keep going, we don't need that one. The Durafets look like this. The chip that you can see in the top picture is just a little window on a stem. The automatic temperature compensation is inside the body of the Meridian electrode. The Durafet is non-breakable therefore if there is anybody on the line that is in the food industry, that Durafet is also available in a 3A package that can be used for food and dairy applications. Other ways of mounting pH probes, glass and/or Durafet, this one has been around for many years. Leads and Northrup originally had it, Honeywell picked it up. It can be used for in line, flow through or for immersion. It can contain either one Durafet or it could have as many as 3 electrodes, a glass, measuring and automatic temperature compensation if you would prefer to use this type of application.

Honeywell also has an insertion removal device whereby removing the pH probe and closing the ball valve you can use what some people refer to as a hot tab. These are available in stainless steel or CPVC, in glass and/or Durafet, again, for quick removal from processes. Durafet and glass electrodes from Honeywell in the combination configuration have a thread at the bottom and a thread at the top. The thread at the bottom can be put into a pipe tee. You want to make sure that the top of that pipe tee is small enough to get the electrode actually into the flow or it can have a pipe attached to it as shown on the left and at the bottom it can be immersed down into a tank. Again, those can be glass and/or Durafet. Honeywell also came up with what they call a twist lock. The metal part stays in the process. The Durafet probe can be inserted with a bayonet quarter turn or removed with a quarter turn for quick access for cleaning purposes. That has been developed here over the past 2 or 3 years. He can have a Kynar, 316 or a CPVC mounting bushing. As you can see, the probe can be inserted into the twist lock housing and turned a quarter turn to put it into application. On the analyzer side, Honeywell has an APT which is a 24 V or 120 V version, 2 year warranty on them. The 24 V can be used by line power, excuse me, 24 V two wire or can be four wires, 120 V. The nicest thing I can say about this it has been around for a long time in the Honeywell family and I am not sure that I have ever seen one fail in all of these years. It also has Hart communications for those of you who need 24 V Hart application.

Honeywell also came out about 3 years ago with what they called then the new analyzer. It is called an UDA 2182. It will actually take two inputs and those can be mixed and matched between contact and conductivity, dissolved oxygen, pH and ORP, NEMA 4X. It also has two analog outputs with an optional third and two relays with an option for two more if you need it. It has also got an infrared communication port so you can upload and download configuration in it. It also has calibration history and vet history. It is very good at being diagnostic. For pH it will give you the slope and the offset value every time you calibrate. We won't touch on this much but the UDA also has either an Ethernet communication port or a Modbus TCP output available to it as an option.

At calibration we touched on the best way to calibrate that is to- let's go with incorrect calibration. Some of the bad things that can happen are inadequate stabilization of the measurement, in other words, not allowing the probe to sit in the buffer long enough. Inadequate rinsing between the probes, if you've got a reference junction contamination, if your buffers are contaminated, if you have let them sit out for a long time. They could be contaminated. Temperature equilibrium and aging probes not being replaced, probes can get old enough that it is hard to calibrate them. A buffer problem, again, you can let the buffer get old. Different temperatures, if you go halfway down it says it can take 45 minutes to 1 hour for a good industrial pH sensor to reach equilibrium especially if you are taking it out of a very hot process and sticking it in a cold buffer.

 A sample is easily contaminated by carbon dioxide such as high purity. The samples should be a continuous flowing sample. Samples should be taken immediately upstream of the in line pH probe. Samples should be kept at the same temperatures as the process and if you are going to walk it back from the lab make sure that it's a sealed container preferably a non-glass and that the temperature is maintained. Again, temperature has a major effect on your measurement of pH. You're measuring electrodes can be bad, can be cracked, they can be old, they can be dirty. Your reference electrode, your reference junction could be clogged. Your reference electrode with potassium chloride may not be compatible with the chemistry. Your reference electrode may have dried up if you have pooled it off the shelf and it has been sitting there for a long time. Again, reference electrode materials could be depleted.

Fouling of the measuring electrode, start with detergent. If you have got wheels on a measuring electrode, use isopropyl alcohol to clean them. If it is really nasty, use a diluted 5% or 10% HCl and water. It should be noted here that if you're using HCl that should only be for a few seconds. I have seen people pick up an application and leave them in the HCl for a long period of time. You can really ruin a pH probe that way. Remember that if your glass electrode is cracked because 0 mV is 7 if you crack a pH electrode it's going to have 0 mV and it will read 7. A couple things to rejuvenate a reference electrode, if you pull it off the shelf and it is dried up one of the things you can do is immerse it in boiling water and many times that will loosen up the potassium chloride and allow you to use it.

I think we are running late here. Let's go through, forget the applications right now. Maybe go through them and hold them for 2 or 3 seconds and just move on. And utilities, of course for boiler feed water and boiler blow down. In pharmaceutical, you can use pH and conductivity both in your working with the reverse osmosis area for RO, for cantion and anion exchange and for softeners. Again, in pharmaceuticals pH can be used and wastewater treatment, for removal of life cultures, for chemical destruction, filtration and final effluent adjustments. Conductivity, we are going to pump through this pretty quick, next slide. Conductivity is basically a resistance measurement. PH is a specific ion for measuring hydrogen ion and hydroxyl ion. Conductivity is a nonspecific measurement for dissolved solids, salts and contaminants. Conductivity is the measurement of the ability of a solution to carry an electric current. The higher the conductivity, the higher the current and again if you are involved in conductivity you know this. Conductivity is directly affected by the number of dissolved ions in a solution. Conductivity is affected by the quantity and mobility of the ions present in the solution and that mobility are generally caused by temperature and again conductivity is temperature compensated. Applications for conductivity, you can pump through this and different applications will pop up. Water treatment, boilers, cooling towers, CIP systems, leak detection and heat exchangers. In cooling towers, many times you are controlling the stink or the bacteria that can develop there. Conductivity is also used in pulp and paper and phase change and pharmaceutical. Conductivity is based again on a number of disassociated ions. The unit of measurement is micro-ohm or microsemiens. There still seems to be some confusion here. Micro-ohm and a microsemien is exactly the same thing. If you are taking a look at 10 micro-ohms, you are taking a look at 10 microsemiens.

We are talking about resistivity here. We are really measuring resistance and converting it into conductivity. The conductivity in some common substances, distilled water is about .5 microsemiens, boiler feed water is someplace between .07 and 5 microsemiens, again alter ultra water. Ocean water is about- watch the change from the U to an M, ocean water is 50 milli-siemens so that is 50,000 microsemiens. So as the water gets contaminated, it goes up in conductivity. If we are talking about resistance, the numbers would be going down. Ultra pure water at .1 microsemiens is about 10 meghoms, 10 microsemiens is about 100 khoms. So you really are measuring resistance and converting it back to conductivity. The conductivity comes in to electrode styles and toroidal. The two electrode style, or what we call contacting, conductivity, or ultra pure conductivity really works on a positive side and negative side going back to your analyzer with the process flowing in between it. We are measuring the amount of conductivity from one place to another using AC voltage as the power. All cells must be mounted so they are directly in contact with the process. Each cell is connected to the indicator or transmitter by either three or four wires. Two wires for the conductivity and basically two wire for the temperature compensator.

These electrodes have a fixed size for simplicity sake let's assume that the distance of electrodes from each other is the same or about one. Your conductivity cell therefore is a one and you would use different cell constants for different measurements. A .01 might be used for 0 to 2 microsemiens. A .1 might be used for 0 to 200 microsemiens. These cell constant of 10 for each plate and the distance between them would give you a cell constant of not 10 but .10 so they bigger the cell, the smaller the amount of conductivity that is measured. Other cell constants are .01, 10, .1, on the market there are some .5 and some fives also. In your toroidal conductivity is the other way of measuring conductivity. It is generally used for high conductivity or dirty solutions where you can't use the contacting type. And you basically have two toroidal, one on the left and one on the right. An inductive magnetic field operates on a different principle than the cells that we were talking about. This one is called electrodeless conductivity. During operation the cell is immersed entirely in the process liquid. The instrument sends an alternating current known value through one of the coils, the primary toroids. This current rates a magnetic field and induces a current in the process liquid. The current in turn induces the current in the pickup coil. So you're basically sending conductivity from the left side to the right side measuring the conductivity and going back to your analyzer again.

It is ideal for corrosive and high conductivity applications. It is also very good in dirty and fouling applications that would foul up a contacting conductivity. Calibration is a means to check both the conductivity measurement for proper calibration. The calibration can be done two ways and we are pretty well wrapped up here. If you want to check your instrument, if you're using an UDA or an APT, you just simply want to check your instrument and make sure it is reading correctly you simply use a resistor and take a look at the reciprocal value. Let's say you want to use a 10K resistor. If you put a 10K resistor on a analyzer it should read 10 microsemiens. If you use a 1K resistor it ought to read about 1000 microsemiens. If you know the instrument is working right then the next thing to do is attach your cell to the analyzer and use a known solution almost like a buffer and get a 25 microsemiens solution and look at the entire system. You can adjust it just like you do pH.

Electronically user resistors for the grab sample, use a standard solution of some known value. It is very difficult in a power plant to use something less than 10 microsemiens or 15 microsemiens solution. If you do, the minute you open that cap you contaminate it with CO2 and once in the air and that sample is no longer good to use so you should use something higher than those very low bottles of conductivity solution. That is just a picture of contacting conductivity, the flow comes in through the right and through the unit and comes out through the hole in the left therefore the water is passing by both of those positive and negative plates. This should be one of the last ones. This is the toroidal conductivity. We have got PEEK: Brown, Teflon, PVDF, and Polypropylene and you would select those to go with your application whichever one is most compatible.

That wraps up the presentation. To open it now for questions and again we thank you for spending time with us and sorry for the problems that we started with in the beginning and because of that we have run over a little bit but we will open things up to questions.

Jennifer:

Yes, thank you guys. So at this time I would like to read some of the questions that came through the chat. We did get quite a few questions asking if the presentation will be available at a later date. We actually did record the entire presentation and it will be up on our website, www.industrialcontrolsonline.com and it will be under the training section. So within the next couple of days, we will e-mail a link to the video and our contact information if you have any further questions. We received a question from Abdul. What is Nernstian effect?

Tony:

The actual pH measurement, the electronic pH measurement was developed by don't know what his 1st name was but his name was Nernst. I assume by that that he is probably German and he came up with the Nernst equation and I can probably get to that. I don't have it as part of this presentation but it is the actual calibration used to measure pH and to generate the millivoltage and the correct millivoltage. Part of the Nernst equation, if he can get me his e-mail address through you Jennifer, I will send him what the Nernst equation looks like but part of the Nernst equation most of them are constants. The one that does vary would be temperature and the temperature will change pH. Basically what they Nernst equation is guaranteeing is the pH that you are measuring at that temperature is reading correctly. I have done some training where we have actually calibrated the pH probe in front of an audience and I will get a cup of coffee out of the urn first thing in the morning before we start and it generally takes us about an hour and a half to get to the section on temperature compensation. I will pour another cup of coffee from the urn and I will put them on the table and I will ask the audience is the pH and both of those cup of coffee the same? The answer to that is no. They will be different pH values, same cup of coffee, same source, two different temperatures, two 2 different pHs and what the Nernst equation does is it says the pH in the cooler water that it reads. Let's say it is reading 4.3, that pH is correct at that temperature. The other one where the coffee is hotter would probably be about 4.7 and in that case what the Nernst equation is saying is that that temperature map 4.7 is corrected for temperature. So that is what the Nernst equation really does.

Jennifer:

Okay, we received another question through the chat from Michael. Is it true you can repair the Durafet pH probe?

Tony:

I don't like the word repair. It can be refilled. It is about the only pH probe that I would refill on the market. As I said before, the potassium chloride job is to leach out so it empties kind of like a fountain pen. The more you use it, fountain pen- listen to me. Ballpoint pen, as you use it you use more and more ink and there is less and less ink available so the Durafet can be recharged and as some people call it refilled. I prefer that you don't wait until the probe is empty because under some pressure as the potassium chloride exits the reference electrode cavity you can get process up in there. The process can attack the silver wire. So what I like to do is, if it is under high flow, high temperature, just check the probe occasionally. Maybe when you take it out and clean it open it up and check it and if it needs more you can tap it and if it needs more potassium chloride I find that Durafet will last longer and work better being refilled if you do it occasionally instead of waiting until it is empty.

Okay, we received another chat question from Thomas. Can the Durafet be used on limestone slurry or gemstone slurry?

Tony:

I have suggested Durafet for limestone slurry applications in central Ohio almost over near West Virginia and it did not function as well as we wanted it to. Honeywell also has a HB probe which is a little heavier duty probe in the Durafet or the standard combination glass. We were getting about 5.5 months in a limestone slurry application using Durafet. We went to the HB probe and it was lasted about 2 1/2 years so for those applications, we didn't touch on that but for those applications I would use the HB probe.

Jennifer:

Okay, we received another question from John. Can you change the constant on a high purity conductivity cell for a higher range and obtain stability in the reading?

Tony:

Let me answer that the way I think I heard it. You match your cell constant for the application. A .01 is generally used in the 0 to 2 microsemiens range, a .1 for 0 to 20, a 1.0 for 0 to 20 and a 10 for 0 to 2000 so it is tough to use a .01 if you are measuring 0 to 10. It will flash on you because it is only made for measuring 0 to 2 microsemiens. However, the conductivity probes have gotten so well made these days and the analyzers with the microprocessors are so well that I have seen a person use a .1 which is generally good for 0 to 20 down in the range of 1 and 2 microsemiens. Most power plant people would not use it for their .7 or .07 conductivity. They would probably use a .01 cell constant but if it is an industrial application you can use the higher cells and lower ranges but I would not use lower ranges in the higher measurements. A matter of fact, you can't.

Jennifer:

Okay, I think we're going to take one more question because we are running a little short on time. We received a question from Arial. Do we need conductivity for treating bacteria and reverse osmosis thus for black and gray water treatment?

Tony:

I think it would be a good idea to take that and find out her e-mail and I will send that to somebody else. I don't know the answer to that.

Jennifer:

Okay. So Arial, if you would just type in your e-mail address and I will go ahead and get that over to Tony so he can get your answer, get your question answered. We do have actually a lot of questions coming through and I don't believe we will be able to get to all of them today because we are running out of time. I just wanted to let everyone know that we are available to answer your questions off-line if we didn't get to them. Joe will be happy to answer any questions you may have and Industrial Controls has a full staff that can answer your questions one on one so fill free to contact us to take the discussion further. The contact information is up on the screen. If you missed any part of today's presentation, we will post a recorded version on our website like I mentioned earlier. Within the next couple days, we will e-mail a link to the video and our contact information if you have further questions or feedback for future webinars. I also do want to mention we have a few more webinars coming up in April. On April 21 we will be presenting part 2 of pneumatic control systems and we will be running another one on how to design an industrial gas detection system for toxic and flammable gases on April 22. We will be sending out e-mail invitations soon and both will be up on our website under the online training section that is www.industrialcontolsonline.com. So I just want to thank everyone for attending today and we look forward to having you back soon. Alright, thanks guys.

 

Speaker(s): 

Joe Callaghan has been with Industrial Controls for 7 years. He is currently the Regional Sales V.P and responsible for Industrial Instrumentation development.  Prior to joining ICD, Joe has 30 years experience with Process Instrumentation including sales, application engineering and also field service engineering.

Tony Walker is a Territory Manager, working for Honeywell out of the Cincinnati office. From 2003 until 2009 he was a Honeywell Product Sales and Application Support manager for the Liquid analytical product line.  Tony has been in the process market since 1973, originally getting in to instrumentation and specializing in Liquid Analytical products when he initially started working for Leeds and Northrup in the early 1970’s.  He has practical experience in Coal fired and Nuclear power plants, chemical plants, water and waste market customers, petrochemical applications, and industrial waste water.  Tony is a graduate of Xavier University in Cincinnati and has lived there most of his life.



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