PH meter
From Free net encyclopedia
A pH meter is a specific type of voltmeter with a very high impedance of the input channels. The high impedance is a necessary part of the equipment because of high resistance of the pH glass electrode typically used with pH meters (usually between 20 and 100 MΩ).
First commercial pH meters were built around 1936 by Dr. Arnold Beckman in the US and by Radiometer in Denmark. Dr. Beckman's invention helped him launch the successful Beckman Instruments company.
The common pH meter has several inputs: for indicator (ion-sensitive or redox) and reference electrodes and temperature sensors such as thermoresistors or thermocouples. Cheaper models require external temperature measurements entered using knob or keyboard.
The pH scale of the device should be calibrated by at least two buffer solutions. Usually one of the buffers used for calibration has pH 7.00 and the second is selected depending on the range where the measurements are to be taken - 10.00 for basic solutions and 4.01 for acidic solutions. This correlates the measured potential of the indicator electrode with the pH scale.