Calibration and maintenance of laboratory pH meter
At present, the indicator electrodes used to measure the pH value of the solution are mostly glass membrane electrodes, and the reference electrodes include calomel electrodes, silver-silver chloride electrodes, and solid reference electrodes. All current electrodes in our factory are in line with glass membrane electrodes. It is convenient to use and maintain. The specific types are as follows: 1. PH electrode calibration There are two types of pH electrode calibration, one is buffer calibration and the other is temperature calibration. Because the measurement of the pH electrode is to convert the activity of hydrogen ions in the solution into a voltage value, and calculate the pH value, the purpose of the buffer calibration is to measure the known concentration of the buffer solution through the electrode, so as to obtain the voltage value , and establish a curve of the relationship between voltage and pH value and store it inside the instrument as the basis for measurement. There are three commonly used buffer solutions: 4.003, 6.86, and 9.182. In the process of debugging the instrument, use two standard solutions of 4.003 and 9.182 for calibration, and measure the buffer solution of 6.86 to see if it is accurate. In actual field application, it is necessary to determine which one or two to use to calibrate the instrument according to the actual measurement of sample water and pH value. If the measured water is acidic, that is, the pH value is less than 7, then use 4.003 and 6.86 buffer solutions for calibration; if the measured water sample is alkaline, that is, the pH value is greater than 7, then use 6.86 and 9.18 buffer solutions for calibration . That is to say, the closer the pH value and pH value of the calibration solution to the pH value of the measured water sample, the better. For the pH measurement process, the most influential factor is temperature. At different temperatures, even a water sample will have different pH values. Therefore, various pH values are equipped with temperature compensation circuits to eliminate this effect. The temperature electrodes used by our instruments to measure temperature are made of platinum resistance. Platinum resistors have different resistance values at different temperatures, so the temperature of the water sample can be calculated by accurately measuring the resistance value of the temperature electrode. When calibrating, input a specific resistance into the resistance box, and input the corresponding temperature value. The instrument will establish the functional relationship between temperature and resistance. When measuring, the resistance value transmitted from the temperature electrode can be calculated to obtain the temperature value. 2. Electrode maintenance There are two types of electrode maintenance, one is maintenance for the first time or after a long period of non-use; the other is daily maintenance. The electrode used for the first time or the electrode used after long-term parking, especially the measuring electrode, because the sensitive film on the electrode surface is in a dry state for a long time, it cannot conduct ions well, and the long-term parking may cause the surface of the electrode to be dirty and the filling liquid leakage etc. Check the electrode filling solution before starting to use it. If the level is too low, it can be added appropriately. If the electrode is stored for a long time, it can also be considered to be replaced. Then wipe the electrode head with a clean alcohol cotton ball, then soak the electrode in its reference filling solution for 24 hours, and use the electrode surface to form a gel layer before it can be used normally. The electrode should be handled with care during daily use, and try not to collide or rub against the measured object. Do not touch the head of the electrode with your hands (to prevent the electrode from being soiled), and do not wipe the head of the electrode with filter paper, etc. (to avoid static electricity that will affect the measurement). When measuring, the electrode should be cleaned twice with the water sample to be tested before measurement. After the measurement, immerse the electrode in its reference solution. It is not recommended to immerse in pure water, so as not to affect the life of the electrode.