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Conductivity Measurement Basics For The Process Industry

The ability of a substance (or solution) to convey an electrical current is determined by its electrical conductivity. Since many years ago, conductivity has been one of the process industry’s most widely used analytical metrics.

Measurements of conductivity represent the total amount of dissolved ionic activity present in a sample solution. This is significant since the measurement method cannot distinguish between particular ions. Conductivity measurements are used in every sector to keep track of water quality, process concentrations, solution cooling breakthroughs, and even wastewater discharge into local streams and rivers. The measurement procedure is accurate, repeatable, and affordable to produce. Conductivity is also affected by process temperature. Integral temperature detectors are a feature of electrodes that allow for continuous measurement and adjustment of the measured value.

The three most popular ways to measure conductivity are examined in the following bullet points, along with the advantages of each measurement methodology.

Two-Electrode Conductivity Measurement Principle

The most popular sensors on the market are two-electrode conductivity sensors, sometimes known as “contacting conductivity” sensors. They are made up of two electrodes spaced at a specific distance from one another. Current between the electrodes is induced when they are submerged in a sample solution. The current increases with the amount of ions in the sample solution, which raises the conductivity value of the solution.
However, the geometry of the two electrodes plays a crucial role in determining the conductivity. The cell constant is the geometric composition. It is both the separation between the two electrodes and the surface area of each electrode. The most crucial element in determining your sensor’s measurement range is the cell constant. The measurement range is tighter the lower the cell factor is (for example, 0.03/cm for high purity applications 0-1,000 S/cm), while the measurement range is wider the higher the cell constant is (for instance, 1.0/cm for typical applications 10 S/cm – 20 mS/cm).

Four-Electrode Conductivity Measurement Principle

Two additional electrodes are added to the sensor by a four-electrode conductivity cell. A current flows through the sample media when an AC voltage is applied to the outermost pair of electrodes. The conductivity of the sample determines how much potential difference is measured by the two innermost electrodes, which are “current-less” electrodes. Afterward, the transmitter takes into account the recorded potential difference and the supplied current. Next, a conductivity measurement that is unaffected by “polarisation” is provided. For applications requiring a wide measurement range, four-electrode conductivity sensors are excellent.

Inductive/Toroidal Conductivity Measurement Principle

“Non-contacting” is a term that is sometimes used to describe an inductive or toroidal conductivity sensor. This is due to the technology’s lack of electrodes that come into contact with the process directly. Two tightly wrapped metal toroids are used in toroidal sensors. These toroids were enclosed in a plastic body that was corrosion resistant. The sensor adjusts measured values using an integrated temperature detector located inside the plastic body.
As the “drive” coil, the first toroid receives an alternating voltage. This produces a voltage that causes an ionic current to flow proportionate to the liquid’s conductance in the liquid around the coil. The “receive” coil is the second coil. Your transmitter measures the electric current that is created when the ionic current is converted to electricity. Due to their resistance to accumulation, toroidal conductivity sensors have a wide measuring range and are excellent for use in filthy settings. We frequently utilise these types of sensors in concentration applications due to their large measuring range.

Summary

Conductivity sensors are crucial in process applications across a wide range of sectors, whether it’s preventing corrosion and scaling in your process or keeping track of the water’s cleanliness. Simply put, choosing the right sensor for your application will depend on your awareness of the key distinctions between the three conductivity measurement technologies.

Naoh Concentration Measurement In Aluminum Extrusion

The forming dies used while extruding aluminium will gather leftover material and other impurities over time. A finished product that doesn’t meet specifications can result from excessive build-up and defects in subsequent extrusions. The dies are periodically withdrawn from the extrusion line and cleaned in a NaOH bath to address this problem. Operators frequently add NaOH to the bath after pumping it into a storage tank at a concentration of 50% or more to begin the cleaning process. NaOH can often be recycled by end users up to a concentration of 15-20%. They will next need to get rid of the used sodium hydroxide.
Sensors that detect conductivity are frequently employed in concentration analysis. Without taking a conductivity reading, the operator can unintentionally apply too little NaOH and improperly clean the dies. Additionally, it’s feasible that they may discard NaOH that is still functional if they didn’t have proper concentration information. The user will waste production time and money owing to lost product or excessive cleaning solution use.

Our Concentration Solution

Utilising the Knick SE 655 Memosens conductivity sensor, M4 Knick is able to detect conductivity with accuracy and dependability in applications ranging from clean water to 2,000 mS/cm. The SE 655 is a toroidal-style conductivity sensor that resists corrosion and has a smooth, hygienic design. Due to the application of the inductive measuring principle, the SE 655 has a high level of accuracy. Low risk of contamination is ensured by the big sensor hole. The sensor is appropriate for dangerous environments. When used with the SE 655 sensor, a Knick Stratos or Protos transmitter shows the conductivity reading as % Concentration of NaOH. This is a well-known industry standard procedure.
The end-user can validate that the providers of NaOH are producing products with a concentration of at least 50% by using a Knick conductivity loop. Additionally, they can maximise the usage of their NaOH before disposal and confirm the efficacy of the NaOH used for die cleaning.
NaOH concentration measurements in other industries:

• Power generation
• Steel Manufacturing
• Pulp & paper
• Food & beverage
• Refining
• Petrochemical & specialty chemical

What was this Customer’s Return on Investment?

Eliminates weak NaOH from the System: Prevents the use of weak NaOH for cleaning, preventing product loss or failed quality inspections.

Reduces Maintenance Costs: The SE 655 toroidal conductivity sensor’s performance under challenging process conditions is good, and its all-PEEK inductive design and construction mean that it needs fewer calibrations.

Enhances NaOH Vendor Quality Control: NaOH shipments that were returned because they didn’t meet specifications are no longer made. In order to minimise downtime, the customer can recognise deliveries of NaOH that are not in accordance with specifications.

Sour Water Ph Monitoring

Improve Sour Water Corrosion Control with Smart Digital pH Sensors and HART/AMS Compatible Transmitters

Steam is a common stripping medium used in a variety of distillation procedures in refineries. The steam is condensed into a liquid by the operators, who then remove it as sour water. The condensate collects ammonia (NH3) and hydrogen sulphide (H2S) during the distillation process.

The Crude Distillation Unit (CDU) is the principal source of sour water. It originates in the atmosphere and vacuum tower during the steam stripping of crude. The hydrodesulphurization units (HDS), fluidized catalytic crackers (FCC), and hydrocrackers all generate a significant volume of sour water.

Our Solution

pH electrodes have difficulty monitoring sour water because particles and sulphides can clog the connection. This may result in sensor drift or failure. This application is perfect for the SE 554 Memosens pH sensor. The open connection architecture of the sensor makes it resistant to media insertion. Additionally, the Silamid® reference is not poisoned by the polymerized KCL electrolyte, which significantly prolongs the life of the sensor.
The pH sensor’s head contains a microcontroller that enables offline calibration and sensor health evaluation. Technicians can calibrate and troubleshoot using a Portavo portable analyzer outside of the process unit, in the lab or shop. More accurate calibrations are possible by controlling the pH of the buffer solutions. After calibrating it, the technician simply transports it to the installation, disconnects the Memosens inductive cable, and performs a “hot-swap” without further calibrating or configuring.

The Stratos Pro is a Class 1 Div 1 FM/CSA rated transmitter that is powered by a two-wire loop. It offers a 4…20 mA output with HART process and diagnostic data overlaid. When employing AMS software, plant operations can see the diagnostic data. As a result, operators can now anticipate maintenance needs, which lowers the risk of unexpected process interruptions.

Refineries must have installations with double block and bleed capabilities. The CSR 3600 is a straightforward retractable ball-valve holder that makes it simple for the user to insert or remove the sensor through a ball valve.

What was this Customer’s Return on Investment?

Reduced sensor replacement and maintenance costs: The Knick SE 554 pH sensor requires fewer calibrations and lasts longer in challenging process settings, which lowers maintenance costs.
AMS HART diagnostics: Clear maintenance requirements are indicated by HART with AMS compatibility. Instead of preventative maintenance, the customer now employs a predictive maintenance schedule. As a result, there are more maintenance man-hours available for other activities because there are fewer excursions to the pH sensor.
Improved corrosion control: The customer was able to lower their capital equipment cost because of improved corrosion control thanks to a consistent pH measurement.

Using Alkaline Buffers For Calibrations Is Not Without Risk

Using buffer solutions with levels that fall within the nominal measuring range of your application is standard practise when calibrating pH sensors. For instance, while performing a two-point calibration, the usage of buffers 4 and 7 is best suited for a measurement range of 5 to 6 pH. The use of high pH (alkaline) buffers is necessary in some applications for two-point or three-point calibrations since not all pH readings are acidic. Here, we’ll go over the volatile properties of these buffers and how to use them correctly to get precise high pH readings.
Aqueous solutions known as buffers keep their pH stable even when modest amounts of acids or bases are added. When technicians calibrate loops in the field where sensor cleanliness can be in doubt, this stability is helpful. While alkaline buffers absorb carbon dioxide from the atmosphere, acidic and neutral buffers are exceptionally stable. The buffer solution’s pH is lowered as a result of the buffer solution’s water and carbon dioxide reaction, which produces carbonic acid. Therefore, a buffer with a high pH value starts to neutralise as soon as it is exposed to air.

Experimenting with Alkaline Buffers 

The graphs below show the effect of carbonic acid over a 24-hour period on 50 mL of a 10.01 pH NIST technical buffer in an open 150 mL beaker. During this time, the pH of this buffer actually decreased by 0.15 pH, going from 10.04 to 9.89.

The slope decreased from 58.7 mV/pH (99.2%), where the zero remained stable, to 55.9 mV/pH (94.5%). Now picture a technician calibrating loops in an environmental discharge or a crucial control point using deteriorating alkaline buffers. At the higher end of the range, this would result in concerns with measurement accuracy.

 Best Practices for Calibration Accuracy 

We talked about pH calibrations with automatic calibration capabilities in an earlier article. When employing alkaline buffers, the following advice is given to avoid measurement errors:

Use different containers to measure things. Never submerge a sensor inside of its storage container into a buffer.
Within a few days of opening, completely consume opened containers or dispose of them. To keep track of passing time, mark any container with the date of opening.

After dispensing, close the containers to stop dust and/or air contamination.
Make use of the tiniest container you can. If use is infrequent, take into account single-dose packages. If use is frequent, take into account dispensers that restrict air from entering the container.
New digital technologies make it easier to maintain sensors and do offline calibrations. Performing calibrations in climate-controlled settings lowers the danger of polluting buffers.
We advise using buffers made by DIN 19266 or the Standard Reference Material (SRM) of the National Institute of Standards and Technology (NIST).
For the majority of applications, technical buffers that are NIST traceable or DIN 19267 are also acceptable. Pay close attention to buffer values in light of the application’s accuracy requirements.
It is frequently sufficient to use buffers 9.00 (at 20° C) or 9.18 (at 25° C) in place of a second or third calibration point. The stability of these buffers is higher than that of those with pH values below 10.0. The data below show how this stability differs from the 10.01 buffer discussed earlier. Over the course of 24 hours, the pH of this buffer 9.00 also decreased, although only by 0.06 pH, from 8.97 to 8.91:
If the state of your alkaline buffer is uncertain, perform a two-point calibration with one neutral (buffers 4 and 7) and one acidic (buffers 4 and 7). Combination pH sensors of the modern era provide dependable linearity. When utilising good buffers 4 and 7, you can anticipate more precision in the alkaline range than when using good buffers 7 and 10.

Summary

The measurement of pH involves several difficult applications and sometimes expensive events. High temperatures and measurements in alkaline regions are known to damage sensors. Environmental discharge that exceeds permissible limits and variations in crucial control points that result in off-spec products are additional expensive incidents. Operations and maintenance staff become upset when measurement differences between grab samples and field instruments occur.

Calibrations work on the same principle as any equation: garbage in, junk out. Inadequate calibrations frequently result in the premature disposal of sensors and the more expensive implications of an inaccurate measurement. For each calibration, use precise and brand-new buffer solutions to ensure you are minimising the cost of ownership.

M4i-RTU Product Highlight

Multi-purpose, easy-to-use digital display, transmitter, and controller

With up to four distinct displays on the front panel, the M4i-RTU allows for the input of up to eight (8) Memosens pH, ORP, conductivity, and oxygen sensors. The MemoRail Modbus transmitters inside the NEMA 4X cabinet may generate up to sixteen (16) variables, which each display is capable of scanning. You can keep an eye on up to sixty-four (64) process variables and diagnostics when using the four (4) display option. The superluminous displays can be seen clearly in bright sunlight, dust, fog, and smoke.
The M4i-RTU functions as a master by reading data from up to 16 slave devices, scaling the data from each, displaying the outcome, and operating internal relays and a 4…20mA output. At a user-programmable scan rate, it sequentially displays all enabled variables. The M4i-RTU acts as a snooper, listening to the Modbus traffic and displaying the precise registers that a master device, like a PLC, is polling.

Features & Benefits

1. Applicable to all pH, ORP, conductivity (non-inductive), and oxygen sensors made by MemosensScan up to sixteen (16) Modbus process variables or sensor diagnostics per display (four (4) screens, 64 variables).

2. Scanner for Modbus RS-485 acting as a Master or Snooper and enabling access to the control system

3. 6-digit dual-line display

4. Useful for usage in direct sunlight, a super-bright LED display, and on-board.

5. ScanView USB programming software

6. three-year guarantee.

M4i-RTU Anatomy

1 – EASY TO USE: Bright display with simple configuration.
The user can adjust the display to their tastes thanks to adjustable register sequencing and scan rate.
either with a PC-based programme or with integrated function keys.

2 – FLEXIBLE: Modular design allows for a variety of input and output combinations.
Using the M4i-RTU, any pH/ORP, conductivity, or oxygen application(s) can be scaled.
There is extension potential by adding more MemoRail Modbus transmitters, displays, or output modules.

3 – INFORMATIVE: All sensor information at a glance.
For each sensor, the primary variable and temperature can both be seen.
There are also available sensor diagnostics such as sensor wear and operation time.

Data Logging For Liquid Analytics

You don’t get any data if you don’t turn on data logging!

I realised I hadn’t launched my data logger when I pushed the stop button on my fitness tracker after finishing an exercise earlier this week. Even though I had liked the workout and felt fantastic, I still felt let down. First of all, I was unable to see the data I needed to assess my performance, heart rate, and caloric expenditure. Second, I had no way of comparing my performance to previous exercises. Thirdly, and most significantly, I lacked the information to submit to my employer’s wellness programme, which meant that I would lose points towards the discount I receive on my health insurance premium!
 The process control industry uses data logging for the same primary purposes:

1. Monitoring
2. Validation
3. Reporting

   You can easily access the pH, conductivity, and oxygen measurement data you need to operate your plant reliably and implement preventative maintenance strategies. We will give concrete examples of how to do this in the paragraphs that follow.

Monitoring with Data Logging

A central control system is frequently not directly connected to many remote operating sites. Organisations instead rely on data recording hardware to capture crucial data for collection and analysis. The data logger is the main source of information in this case.
The Knick Stratos Multi and Protos transmitters are suitable for monitoring, controlling, and data logging in remote operating sites. Operators can record measured values from each channel in a format and interval they choose by activating the Measurement Recorder feature in either of these transmitters. For sensors you may record in parallel with the measured values, Memosens smart digital sensors also offer health and diagnostic data. Data is saved on the memory card safely and securely. The card enables for an easy USB export to your PC and a minimum of 20,000 entries (depending on settings and periodicity).
A Portavo portable metre can be used by field service professionals to record measurement and diagnostic data from their sensors while they are on the job. A Portavo is suitable for usage in Class 1, Division 1 situations. The information gathered in the Portavo can then be returned to a central location and exported as a CSV file, an Excel spreadsheet, or the MemoSuite programme.

Data Validation

Data loggers may be useful as a secondary source of information that can be compared to other sources of data for verification needs. This can be done as a trend through time or a static (single point) comparison. These validation data can be used to verify whether your inline measurements require calibration or repair if you are monitoring a crucial process parameter.

When doing routine maintenance or addressing a particular performance issue, a technician might take a Portavo portable metre into the field. They now have a third source of data to compare to the process reading and lab measurement after obtaining a sample of the process and measuring and data logging with the Portavo. Now that the process measurement has been validated, you have it quickly and accurately.

Reporting using a Data Logger

Reports for customers or regulatory agencies can be produced using data loggers. For instance, the EPA or a nearby municipality might require your data to demonstrate that you adhere to emissions or outfall limitations. Similar to this, your buyer can need proof that you satisfy their product specifications.

Knick makes it simple to automate the reporting process, regardless of whether data are being logged in a field transmitter or portable metre. Just export the data from our devices to an Excel or CSV file. You can also offer calibration certificates that are in compliance with 21 CFR Part 11 using the MemoSuite software. Using the programme, you may quickly and precisely supply the information required to regulatory agencies or your clients.

Summary

Implementing a data logger is a fantastic idea for gathering crucial information from distant locations, confirming process measurement data, and ensuring secure reporting. Let us assist you in choosing the appropriate fixed or portable tool to carry out the necessary tasks.

Without my fitness tracker, I’m sure I was just fine. But now I am certain of my performance today. I can also check how that measures up to how I’ve performed in the past. But most importantly, I now have the knowledge required to qualify for my insurance discount. All I have to do is make sure I turn it on!