Over the recent years, there are many questions from user with regards to the usage and selection of multiparameter meters, which consists of measurement typical parameters, such as pH, ORP, Conductivity, TDS, Dissolved Oxygen, temperature.
- Can I calibrate the pH of the multiparameter meter using a single pH buffer?
The answer is No. Most multiparameter in the water industries consists of at least 3 point calibrations, which generally covers from 4 to 10pH. So, it is imperative to conduct at least a 3 points calibration for the pH sensors, and it should cover the range from 4 to 10pH. In the market, most industries players will provide near 7.0 pH solution as a standard encompassing with Conductivitiy solution that falls around 5mS/cm. This type of quick or rapid solution will only be a urgent verification or calibration solution to bring along when you need quick verification in a remote place. It is not meant to keep your multiparameter meter in check, since you will not be able to find out the correct offset and “health” of your pH sensor. Without at least 2 points calibration on the pH, you will not be able to figure out the offset and slope of your pH sensor. In that sense, you are not able to determine when you will need to replace your sensor. A defective or worn-out sensor will fall within 6 to 7 pH, and this will jeopardise your measurement integrity. As for the Conductivity measurement, it is important that we calibrate the meter nearest to our sample measurement as much as possible. For instance, if we are measuring potable water, we can calibrate the Conductivity parameter with the nearest available EC solution, such as 1,413uS/cm, which can be readily available in the market. If we are measuring seawater, we should calibration our Conductivity at least around 52mS/cm.
- When do we know when to record or log the reading?
There are many types of built-in features in many types of models of multiparameter meters. Having been using such meters for many years, I would advice user to standardise your measurement method, by understanding the stability readings on your meter instead. As it implies, a multiparameter meter will cover a few parameters, and the stability time for each parameter will be different, especially the pH and DO parameters. Some meters automatically log-in or hold the readings once it reach stability on one or two parameters, but in actual fact. We have to ensure all parameters are in stable condition (readings stability) before we log in the results. And how do we determine that? I will say, standardise the way you log in the result by having the habit to store it after taking the readings for about 2 mins or more, depends on the general stability of your sample and sensors. In this way, you will have a consistent results throughout all your measurements, and not being limited to the algorithm of the meter instead.
- Is Optical DO better than membrane type DO sensor?
I personally will recommend user based on their usage experiences on either type of DO sensor. Because both types have their pros and cons. As a thumb of rule, for new user of the multiparameter meter, I would recommend user to try out the optical DO sensor because no refilling of electrolyte and membrane cap replacement are needed. And an optical DO sensor replacement time is around a year. This makes it much easier to maintain when user does not have the knowledge in maintaining membrane type DO. However, if a experience user has been using membrane type, such as galvanic type DO sensor, and they already knew the type of tasks need to maintain continue working condition of the sensor, such as adding of electrolyte solution, replacement of membrane cap once every month (if sample is harsh), ensuring no bubble are present when replacing the cap, constant calibration (no solution needed) to get a stable reading. The price difference between the two types are great, therefore do ensure you get good trainings and understandings of how your meter works. The meter will stay with you for long time if TLC is given to them 🙂
H2O Engineering & Trading 