How to measure the pH value of high-purity water

In pure water systems, pH measurement is often used as a tool for diagnosing contamination. Ensuring the accuracy of pH measurement is crucial for the entire system.

If the purity of water is very high, it can be monitored by measuring conductivity or resistivity, and there is no need to measure pH again.

So the measurement of pH value is usually used as a tool to diagnose whether there is contamination, that is, whether there is acid or alkali pollution on it.

It can be used to diagnose the source of pollution. In addition, pH is also a very important control parameter for the final purification process.

The following factors can ensure accurate online measurement of the pH of high-purity water:

The measurement point should be in the bypass system and the medium can be discharged. Because the operation of the electrode reference system requires a constant and low pressure, and the sample will be contaminated by KCL solution in the electrode.

To prevent carbon dioxide in the air from contaminating the sample and causing a decrease in measurement values, the sample should be sealed.

The flow through sheath should have good shielding performance (such as stainless steel) to prevent electrical interference and potential effects.

Due to the high measured impedance and susceptibility to interference, the cable connecting the sensor to the transmitter should have good shielding performance.

The flow rate of the sample needs to be low and stable, as excessive flow rate can cause electrostatic effects.

There should be reserved channels to separate the KCL in the reference electrode from the sample, in order to prevent the influence of KCL on the measurement.

The preamplifier of the transmitter needs to provide high impedance input for both the pH meter glass electrode and the pH meter reference electrode.

If the reference value is a pH value below 25 ℃, the Nernst equation needs to be used to compensate the pH value to a value below 25 ℃.