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A pH meter works by associating a voltage with a pH value. The more ions that pass through the membrane, the higher the pH value, and vice versa.
How Accurate Is A pH Meter?
pH meters use a computer or digital user interface providing you with an instant pH reading on a readable display, therefore, they are considered extremely accurate and durable as long as you store them properly and maintain them according to the manufacturer’s guidelines.
As mentioned, pH meters must be calibrated using a standardized buffer. A buffer allows the meter to associate the voltage of a solution with a pH value. pH meters may slightly differ, but they are usually all accurate to the hundredth place. pH meters can be affected by ion interference sometimes drifting from the calibration position, hence it is important to always calibrate your pH meter before use.
Some pH meters require to be plugged into an outlet, while others need batteries, which are commonly used in the field. pH meters accommodate different industries depending on the application.
Advantages Of Using pH Meters
pH meters are simple to use and are not affected by human error such as color blindness. Some people may perceive color differently from others, or the true result. As pH meters use a readable digital display, they provide a much more precise result than pH papers and titration methods.
As pH meters are portable, providing quality precision readings wherever you need to test pH solutions is easy. They can be used in a controlled laboratory or used for environmental field-testing. If you will be in the field, small battery-operated pH meters are ideal for hauling to different locations.
Disadvantages Of Using pH Meters
pH meters cost a lot more money than pH paper strips, as a pH meter is a long-term investment to provide accurate pH readings. If you only need to take occasional pH readings such as in home aquariums, pH paper may be a better alternative.
Another disadvantage of using pH meters is maintenance. You will need to clean it regularly to avoid possible contamination of samples. As most pH meters contain a probe with a glass tip, these are extremely fragile so can be easily broken or damaged if exposed to corrosive substances.
Lastly, pH meters must be calibrated before use, which is vital for obtaining accurate results. If a pH meter is not calibrated properly, the results can be distorted. To prevent human error when using a pH meter, always refer to the operating manual for detailed instructions of use.
Why calibrate your pH meter and how!
What is calibration?
A pH calibration is the process of adjusting your Manual Calibration PH Meter by measuring solutions of a known pH value. This is because the characteristics of your electrode will change over time and this needs to be compensated for. A calibration does this by matching your pH meter to the current characteristics of your pH sensor.
What types of calibration are there?
There are single point, two point and multi-point calibration when it comes to pH meters. Essentially this is how many points a calibration is performed at. A single point calibration can be used when you are looking to measure a consistent pH value with little variation. This method involves only using a single buffer solution as a reference for calibration.
The most common pH meter calibration is the two point calibration and is best suited when you have a range of pH samples. The buffer solutions should bracket your expected pH sample. In this process the pH meter determines the slope and offset error for the actual pH electrode in use. This information then allows the meter to adjust the mV/pH equation of the pH meter to match the characteristics of the electrode in use.
If you are bracketing a wider range of the pH scale a multi-point calibration covering this range will give you the most accurate and repeatable results. This is where 3 or more calibration points are done and gives the pH meter a more accurate mV/pH equation over the range you are looking to cover.
Performing a Two Point Calibration
Turn the pH meter on and enter the calibration mode on the pH meter
Select two pH buffers that bracket the expected sample pH. The first buffer should be pH 7.00 (your neutral/zero point) and the second buffer should be near the expected sample pH (pH 4.01 or pH 10.01).
Before starting calibration, be sure the sensor and the buffer solution are at the same temperature. If not, allow time for temperature equilibration. If you have a meter with ATC (Automatic temperature compensation), the meter will compensate for the temperature difference and as such you can skip this step.
Pour the necessary amount of buffer solutions into individual glass beakers. Buffer solutions will remain stable in a glass beaker for a maximum of 2 hours. Please note: Never carry out calibrations in the bottle of buffer solution as this will taint your solution and significantly reduce accuracy and do not pour used solutions back into the bottle, discard them and use new solution each calibration.
Place the electrode into the pH7 solution you have decanted. When the reading is stable, set the pH meter to the pH7 value.
Remove your electrode and rinse it with distilled water
Repeat step 5 with your next buffer.
When the pH meter calibration is done, rinse the electrode and place into the sample and take your pH measurement.
Selection and care of pH and EC meters
Growing media samples can be easily sent off to a laboratory or you can test your own samples with portable pH and EC meters. If you test yourself, there are many types of pH and EC meters available on the market. Some are more expensive than others with prices ranging from $45 to $600. Selecting the best one(s) for your application depends on your needs and planned usage. The advantage of having your own testing equipment is that the results are available in real time so you can monitor and make adjustments to your crop(s).
pH meters: Pocket or portable meters (a box with an external wire running to the probe) are small in size and convenient. There are also non-portable, desktop models which are more expensive and offer more precision, but may be overkill for most applications. The best pH meters are those calibrated with at least two standards, such as a pH 4 and pH 7. Accuracy between these standards is good. Meters calibrated with one standard are only accurate near that standardized value, so this type of meter is not the choice. Another consideration is to purchase a meter with a replaceable electrode since its life expectancy is from one to three years, depending on how often it is cleaned and if it is stored in a storage solution.
Avoid inexpensive pH meters with thin metal probes that are pushed into the pot. They are designed for testing saturated media but are not very accurate. In addition, most of these meters cannot be calibrated to verify their accuracy.
pH electrode care: Most pH electrodes encased in glass or plastic need to be stored in a storage solution or a standard calibration solution. Never store the electrode in distilled water or let it dry out. If it dries out, it may require an hour or two of re-soaking in storage solution before it will provide reliable readings. In the worst-case scenario, improper storage can ruin the electrode.
There are a few portable pH meters with electrodes that can be stored dry. For some growers, this may be more convenient even if the meter is more expensive. Again those calibrated with two standard solutions are more reliable. The metal electrode will require periodic cleaning and avoid touching it as it is sensitive to electrostatic discharges.
EC meters: EC meters are also available in pen, portable and desktop models. Prices for pens and portables range from $50 to $400. Almost all EC meters are calibrated with only one standard solution. Select a meter whose range of measure covers most greenhouse applications (i.e. 0.5-5.0 mmhos/cm). It should have an automatic temperature compensator since the EC of a sample approximately doubles for every 55°F (13°C) change in temperature. Many EC meters have the ability to measure TDS (Total Dissolved Solids),they are called TDS EC Meter.
General meter usage tips: Regardless of the type of meter, do not store them in the greenhouse, where humidity can interfere with electrical signals and shorten the life of the meter. Each meter should be calibrated before use and after extended storage periods (at least once per month). Remember to use fresh standards to calibrate each meter. The more frequently a meter is calibrated, the more accurate the measure.
Using pH and EC meters are key grower tools for monitoring water, fertilizer solution(s) and growing media. The benefits of these meters far outweigh the initial cost. Measuring pH and EC values allow the grower to make adjustments and fine tune inputs for best crop results.
Advantages of TDS measurement of water | Total dissolved solids
Introduction: Water is universal solvent which has ability to dissolve molecules from different kinds of substances. It is essential to have adequate level of TDS in water to assure taste, color and odor. TDS levels between 300 to 500 are considered to be safe for drinking purpose.
What is TDS ?
The term TDS refers to Total Dissolved Solids. It indicates amount of organic/inorganic materials dissolved in particular water volume. These include metals, ions, minerals etc. TDS in water is due to minerals in springs, chemicals used at water supply source, road salts, fertilizers, plumbing etc.TDS is measured as volume of water with unit milligrams per litre (i.e. mg/L). It is also known as ppm (parts per million).
TDS measurement using digital TDS Meter
The figure depicts digital TDS meter used to test water purity. It uses polypropylene as filter material. TDS meter measures water quality in units of parts per million (ppm) or mg/L. It finds many applications which include water purifiers & filters, food such as vegetables and fruits drink quality monitoring, spas, pools, aquariums, hydroponic and so on.
Benefits or advantages of TDS measurement
Following are the benefits or advantages of TDS measurement method used for drinking water quality measurement :
➨Water with very low TDS will have flat taste and it lacks in minerals. Moreover water with high TDS is unsafe due to contamination and is not recommended for use. TDS measurement using TDS meter helps us maintaining water with right TDS for our usage for cooking as well as drinking purposes.
➨Flowers and plants require 1000-1100 ppm and 900-1000 ppm respectively. TDS measurement helps in watering vegetables and flowers with appropriate nutrients.
➨It is used to measure TDS level of water coming out of your tap or source of water. This helps to buy appropriate water purifier for your need and avoids unnecessary expenditure.
➨It helps to regularly check the water output from the purifier so that we will come to know when to replace the purifier or change its parts.
➨It helps in keeping proper TDS level of water in your fish tank similar to natural habitat.
➨High TDS water having high levels of magnesium and calcium is known as hard water. This hard water gets collected in pipes. This results into expensive replacement of pipes and also reduces lifetime of home appliances.
Conclusion: From above discussion of advantages of TDS measurement using TDS meter, one can conclude that it is very much essential to have TDS meter for our daily life.
Information About Salt Meters
There are a few kinds of salt meters that differ in their measurement principles and methods.
1) The Mohr method / silver nitrate titration measures the amount of chlorine (the Cl in NaCl).
2) The ion electrode method measures the amount of sodium (the Na in NaCl) to ascertain the salt concentration.
3) The electrical conductivity method uses the fact that salt (NaCl) can conduct more electricity than other substances to ascertain the salt concentration by measuring the electrical conductivity.
4) The refractometer method uses the fact that the refractive index increases with solubility in an aqueous solution to measure the salt concentration by measuring the refractive index.
ATAGO offers salt meters that use 3) the electrical conductivity method and 4) the refractometer method.
Features of Salt Meters Using the Electrical Conductivity Method
Salt is an electrolyte, so there is a correlation between electrical conductivity and salt concentration.
Electrical conductivity is a scale for measuring how much electricity is flowing through a medium, and it is the inverse of electrical resistance (electrical conductivity = 1/electrical resistance). The electrical resistance of a distance between electrodes of 1 cm is called an ohm centimeter (Ωcm), and the inverse is called the specific conductivity.
That value multiplied by 1 million is the commonly-used electrical conductivity (microsiemens: μS/cm).
If the electric resistance for 1 cm is 1 million Ωcm, then the specific conductivity is 1 millionth, and electrical conductivity is calculated by multiplying that by 1 million, resulting in a value of 1 μS/cm.
The Advantages of an Electrical Conductivity Salt Meter
＊Electrical conductivity has an especially large advantage over the Mohr method (silver nitrate titration).
・ The instrument is portable.
・ Measurements can be taken anywhere.
・ Measurement takes only 3 seconds.
・ A reagent is not necessary.Reagents usually cannot be brought onto the production floor. In addition, as a consumable a reagent adds another running cost to production, and the disposal of the reagent is not environmentally friendly.
・ No need for a titrator or scientific tools such as pipettes.
・ The measurement is automatic, so there is no discrepancy between testers.In the Mohr method, the end point is determined by a change in color, so inexperienced testers can make mistakes when measuring. With the electrical conductivity method, measurement is automatic, causing no discrepancies between users and requiting no experience.
・ Anyone can easily take measurements.
・ Only 0.3 mL of liquid is needed for measurement.
・ Just wipe the electrode with water or alcohol.
・ Easy to clean and store.
・ Lower cost than automatic titration equipment.
Most salt meters using the electrical conductivity method use gold plate electrodes, but a major feature of ATAGO’s electrical conductivity salt meters is that they use titanium electrodes.
Gold plate electrodes are easily scratched after years of use, and once the electrode is scratched, the measurements fluctuate and are no longer precise. ATAGO’s Salt Meters, however, use titanium electrodes that are scratch-resistant and extremely durable—the failure rate of ATAGO’s Salt Meters is only 0.1% within 3 years after purchase.
Caution must be taken when using electrical conductivity salt meters when measuring liquid solutions that contain other electrolytes. For example, if there is 1 g of monosodium glutamate in 100 g, it will add about 0.16%. Actual foods, however, do not have as much as 1 g in 100 g, so it can be disregarded.