| Hanna Part No: HI-221
A pH electrode, when it is properly manufactured and kept clean, will retain its physical characteristics for a long time.
A common problem associated with pH measurements is the use of a pH electrode that hasn't been properly cleaned. This is very important because, during calibration, the instrument assumes that the elcetrode used is clean and that the standardization curve created during the calibration process will remain the same until the next calibration.
pH meters on the market today will allow an offset of approximately +/-60mV. The deviation from 0 mV is not unusual, in fact it represents the true characteristics of the pH electrode.
The deviation from 0 mV becomes a problem if it is the result of calibrating a dirty electrode.
The figure below shows that the pH measured by a dirtly electrode changes over a period of time. This results from the residue on the pH electrode bulb dissolving into the solution and the electrode gradually returning close to its true characteristics. The resulting pH measurements, based upon the calibration of a dirty electrode, will then be incorrect.
The HI-221 compare the characteristics of the pH electrode from one calibration to the next. In case of large variances in electrode condition that can only be the result of dirt, these meters alert the user that the electrode needs to be properly cleaned prior to the calibration porcess.
How does the Calibration Check work?
The HI-221 is able to detect a contaminated calibration buffer solution.
When a pH electrode is dirty, it has a slow response time and unstable reading. The HI-221 warns the user in the event of a dirty electrode.
Calibration Check Features:
Electrode offset & slope condition
Electrode response time
Calibration time-out
During calibration, the user is advised whether one or more parameters are unsuitable to perform the operation.
The HI-221 is supplied complete with HI-1131P refillable pH electrode (glass-body, BNC & Pin with 1m cable), HI-7669/2W stainless steel temperature probe, HI-76404 electrode holder, pH 4 and pH 7 buffer sachets, electrode refilling solution, 12 Vdc adapter and instructions.
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