Electronic Testing in Water Analysis

Does the unit require periodic calibration and, if so, how difficult is it to perform? Know how often it is recommended for a particular unit. As noted above, you may also want to know the cost of calibration standards in advance so you are not surprised when you have to spend $40 or more on the appropriate standards. Some units may require calibration from the manufacturer. If this is the case, you will need to plan to send the meter away during a downtime or off-season, or perhaps you’ll acquire a backup instrument for the times that the meter is away. You may also want to ask the manufacturer how long the typical calibration will take, and if there is any associated cost.

Limitations

Like accuracy and precision information, the limitations of any instrument should be readily available. Pay careful attention to the operational ranges of the instrument to ensure they meet your testing needs. Also, take note of any interfering substances that may affect test results. It would be unwise to purchase an instrument that is not recommended for use when hardness levels of water exceed 500 ppm if the hardness in your area is at least that high straight from the tap. Manufacturers may not be as forthcoming with the interference information, but you should be able to find it nonetheless. For example, the pH and temperature limitations for Oxidation-Reduction Potential (ORP) are well-documented, and plenty of information is available on this topic.

The Instruments

Taking all of these factors into consideration, you can make a wise decision about the meter that best fits your testing needs. Regardless of the instrument you choose, the real benefit is the elimination of the “guesswork” typically required. For example, many users find comparing a reacted color to a color standard difficult, if not impossible. Instruments may be ideal for those with poor color acuity or some form of color blindness.

Sensors/Electrodes

For some of the parameters regularly measured in pool and spa water, an analysis can be performed with the simple push of a button. For example, pH can be measured by a portable pH electrode partially submerged into the pool or spa and the appropriate button pushed to activate the reading. Unfortunately, this technology does not allow for testing of all important parameters in pool and spa water. Typically, these sensors will only measure pH, total dissolved solids (TDS), salt, ORP and temperature.

The latest in sensor/electrode technology allows some or all of these parameters to be measured on one unit at a price that is not a major investment. Several manufacturers now offer systems capable of measuring pH, TDS, salt, ORP and temperature in seconds, all with the same instrument. The least-expensive of these instruments typically sells for around $350.

ORP and pH are measured in much the same way by these types of systems. Voltage is generated between a reference electrode and a measuring electrode with pool water between. A change in the current equals a change in the measured value. Even though there are two electrodes, these are often contained inside a single unit, giving it the appearance of only one probe. It is important to point out that ORP does not replace regular monitoring of free available chlorine. Regulations require testing free chlorine, even in systems fit with ORP-monitoring ability.

Conductivity results are used to approximate TDS and salt. Conductivity is the measure of the water’s ability to conduct an electrical current. A reference solution with known concentrations is used as a calibration standard. The unit then assumes the water “make-up” is similar to that of the standard, and measures its ability to conduct an electrical current, which is converted into a salt or TDS reading, depending on the setting and calibration. Unfortunately, this is really just an approximation, as conductivity is not a direct measurement of TDS or salts. However, it is a fast and easy method that can provide a close approximation.

· Advantages–Electrode systems provide near-instant results for the parameters they are capable of measuring. Often, several parameters can be measured by the same unit by switching modes. No additional reagents are needed for regular testing. The results also can be highly accurate and precise, depending on the instrument. These instruments are typically easy to use and operate with little or no training required. This technology is also suitable for continuous online monitoring.

· Disadvantages–The electrodes require careful handling and cleaning/rinsing with distilled or deionized water after each use. It is also important to carefully follow the manufacturer’s recommendation for storage of the electrodes. These systems also require periodic calibration, and it may be difficult to tell when they are not reading accurately.

Colorimetric Tests

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