pH measurement / pH meters and electrodes

What is ATC on a pH meter?

Q: What is ATC on a pH meter? Should I be looking for a meter that has this?

testing pH of river water
When testing pH, what is ATC? Why is it important?

A: ATC stands for Automatic Temperature Compensation. This means the meter measures pH and temperature at the same time, then automatically calculates to correct for differences (e.g. if one sample is 20°C and another is 23°C).

pH meters that do not have ATC are markedly less accurate.

Why measure temperature when measuring pH?

Temperature affects pH in a variety of ways – for a detailed look at them – see this article. But overall we can say that the two most important things to remember are;

  • Keep your samples and calibration buffers as close in temperature as possible
  • Use a meter with ATC to compensate for the remaining small differences

How does ATC work?

When a sample is tested, the pH electrode and the temperature probe should be placed into the sample and stirred to achieve a stable reading. As long as ATC is enabled on your meter, the calculations to correct for temperature will be done automatically and you can simply read the pH value on the meter.

Some electrodes are “3-in-1” which means they have a temperature sensor built in to the pH electrode, so you will see only one probe to put in the sample.

Most pH electrodes are “2-in-1” and will have a separate temperature sensor – both must be placed in the sample for the ATC to work.

ATC on a pH meter
Most pH meters with ATC will have a temperature sensor (usually a slim metal probe, left on the above) as well as the pH electrode (may be glass or plastic, right on the above) – both must be placed in the sample for ATC to work and achieve accurate results.

For many meters this means holding two probes on cables in your hand to put in the sample.

The TRUEscience pH caps (shown above) have the fixed temperature sensor  held close to the pH electrode along with a clip to attach the whole cap to beakers. This makes sure that both pH and temperature are always measured at the same time.

pH Meter
pH Meter

For more information about pH testing, follow the links above or contact us if you have any questions;