PH Meter Calibration

pH Meter Calibration Service

The longer a pH meter is in use, the higher the probability that measurement errors will occur. This is simply because the liquid it contains ages and the level of contamination is constantly increasing.

Since in many industries inaccurate readings would be cataclysmic, it is necessary to calibrate the pH tester – and that also means frequent cleaning of the PH electrode. There is little difference in procedures between devices and Premier Calibration Sdn Bhd is capable of calibrating the pH meter.

Is it important to calibrate the pH meter?

Although the terms “validation” and “calibration” are often used synonymously, they are completely separate processes. The validation can be carried out regularly on your own in order to enable permanently accurate measured values. If inaccurate measurement results should actually occur, this is in principle not associated with any legal consequences.

On the other hand, there is the calibration of the pH measuring device, which must be carried out by a third party specialist like Premier Calibration Sdn Bhd. During calibration, the device is tested in an official test to determine whether it meets the legal requirements. If this is not the case, it must not be used further.

How often do you have to calibrate the pH meter?

Unlike the buffer solution, there are no standards or legal requirements for the frequency of calibration. It makes sense to calibrate the pH tester regularly: This is the only way to prevent inaccurate readings and the negative impact on the quality of products or research results. The service life of the measuring devices can sometimes be greatly reduced if this maintenance step is omitted.

The ideal time interval for a new calibration depends on several factors. These include, for example, the frequency of use and the need for absolutely exact measurements. It is usually suggested to calibrate pH meters at least twice a month. But daily cycles can also be appropriate.

In addition, the question “How often to calibrate the pH meter?” can be answered by referring to specific cases, i.e. when one or more of the following circumstances become noticeable:

A new electrode is used or installed
A few days have passed since the device was last used
The existing electrode has just been cleaned
A measurement was made in a strong (acidic or basic) solution
The subsequent measurement must have a particularly precise result
Calibrate pH meters correctly and regularly

Calibrating the pH measuring device not only results in high measurement certainty: it also increases its durability, which is profitable in monetary terms. It is important to pay attention to a suitable procedure and to choose the right time intervals. Then nothing stands in the way of optimal measured values with all device types.

During pH meter calibration, two points are determined between which a linear voltage curve can be generated. This ensures that the output pH value is accurate again – and is not incorrectly displayed due to aging liquids or dirt.

To calibrate a pH meter, the electrode must first be immersed in a pH 7.0 buffer solution and then rinsed. These two steps are repeated with the second buffer solution having a pH of 4.0 or 10.0.

The correct time interval depends on the amount of use and the need for absolutely accurate readings. Although the calibration of the pH electrode should be carried out at least twice a month, a short interval of one day can also be used.

Premier Calibration Sdn Bhd is experienced in calibrating pH meters and follows the international standard in calibrating pH meters.

COMPLIANCE: ISO/IEC 17025:2005 ACCREDITED

We are an accredited, SAMM (Skim Akreditasi Makmal Malaysia) Malaysia-based laboratory, with very well trained and experienced technicians able to accomplish your temperature and humidity calibration both on-site and in our laboratory. We calibrate all types of temperature and humidity instruments regardless the industries, for instance Food and Beverage manufacturing industry, Pharmaceutical, Chemical plants, both private and government Hospitals, both private and government Laboratory, Testing laboratory, Commercial Kitchen, Hotels, Quarry, Palm Oil Industry etc.

The basic process of Calibration pH Meter is as follows:

Adjust temperature: It is important that the buffer solution and the instrument have exactly the same temperature during calibration. This should ideally be achieved with an automatic temperature compensator.
Check the electrode: The first step is to check the electrode. If this is defective, it must be replaced.
Preparation: If a new electrode is used, it must first be stored in a beaker with storage liquid for about four hours.
Setting: The device must then be set from MTC (Manual Temperature Compensation) to “ATC” (Automatic Temperature Compensation) or “pH” so that it can work automatically.
Immerse the electrode in pH 7.0: Next, a clean electrode is placed in fresh pH 7.0 buffer solution. The pH meter reading must also be set to exactly 7.0. The voltage at this measurement point represents the baseline.
Rinsing (one-point calibration): The first rinsing of the electrode with demineralized water follows. The first part of the calibration – the so-called one-point calibration – is then completed.
Immerse the electrode in pH 4.0: The two-point calibration follows. To do this, the same electrode is now immersed in a buffer solution with a pH value of 4.0 (or optionally 10.0). Again, the correct reading must be set on the meter.
Rinsing (two-point calibration): Finally, the electrode is rinsed a second time. The two-point calibration is then also completed and the pH meter is ready for use again, since two measuring points were determined for the linear course of the voltage.

To calibrate a pH meter, the electrode must first be immersed in a pH 7.0 buffer solution and then rinsed. These two steps are repeated with the second buffer solution having a pH of 4.0 or 10.0.

Premier Calibration Sdn Bhd is experienced in calibrating pH meters and follows the international standard in calibrating pH meters.

Calibrate pH meter: Digital and Manual

With pH meters, another distinction is also possible – between digital and manual measuring devices. Although these differ slightly in structure, there are only minimal differences in the respective calibration.

Digital pH meter

Digital pH meters are extensively available and can vary not only in size and construction, but also in design and price. When it comes to calibration, however, all devices are similar, which makes the process easier. The probe at the end of the pH meter is simply dipped into the buffer solutions. The measurement takes place at the touch of a button. It is important to set “ATC” or “pH” beforehand.

Manual pH meter

Manual pH meters typically do not have a head that can be used to calibrate the pH electrode. Instead, a screw on the device located at the end of the pen must be loosened. As soon as the measured value matches that of the solution, the measurement can be ended and the screw tightened again.

pH Meter Calibration: buffer solutions

Buffer solutions are required to calibrate a pH meter. These bear their name because they can both keep a pH value stable and buffer it. These special solutions are standardized according to DIN 19266, which makes them easily reproducible. Uncertainties are at most 0.005 pH units. The following factors should be considered when selecting and using buffer solutions:

Order of Use: Literally, it doesn’t matter what order the buffer solutions are used in a two-point calibration. It is only important that the voltage is determined at least twice. Whether the pH value 7.0 or 4.0 or 7.0 is used first is irrelevant.

Composition: The composition is also specified in DIN 19266. According to this standard, a buffer solution consists of either:

from a weak acid and a conjugate base
OR from a weak base and a conjugate acid.

Temperature: In addition, attention must be paid to the temperature of the buffer solution. The linear value is given for 25°C, so the calibration of pH meters should also be carried out at 25°C. If there are temperature differences, large errors in the measurement results can sometimes be expected.

Calibration of the pH electrode using different methods

DIN 19269 specifies how to calibrate the pH value. A number of methods are also given there by which the process can be carried out. In addition to a one-point calibration, the two-point calibration described above and a multi-point calibration are also possible.

One-point calibration

In a so-called one-point calibration, only a single buffer solution is used, which is used to determine the zero point of the pH electrode. From there it is assumed that the slope is the same as the Nernst slope, i.e. the theoretical value of the electrode slope. Although this method saves time, it should only be used when several identical solutions are to be checked.

Two-point calibration

Two-point calibration is carried out using two buffer solutions with different pH values. A linear gradient and a zero point can be determined between the two measuring points, from which the output value of the pH electrode is calculated. This method is usually sufficient to calibrate the pH value and achieve high measurement accuracy.

Multi-point calibration

It becomes even more specific with multi-point calibrations that use several (mostly alkaline) buffer solutions as a reference. The pH difference between each solution is 0.5 or more. Adjacent segments are formed within which the slope and the zero point can be determined. As a result, particularly precise measured values can be achieved.