The pH electrode is a glass electrode which is constructed from three different glass types to be applicable in soils. The actual measuring tip consists of a robust and long-term stable membrane glass with a large wall thickness. For field use, the glass electrode is inserted into a protective sleeve which can be extended to a length of 100 cm by means of a PVC-shaft.
Between the glass membrane and the cylindrical glass shaft, a third type of glass (transition glass) was added, whose expansion coefficient lies between the coefficients of the other two glass types and thus is able to buffer stresses occurring during temperature fluctuations. For field use, the glass electrode is inserted into a protective sleeve which can be extended to a length of 100 cm by means of a PVC-shaft.
The development of the ecoTech pH electrode, Item no. 465, began in 2008 and closely followed the electrical design of the platinum redox electrode, proven since 2005. Thus, as the redox electrode, the pH electrode is a two-probe electrode, in this special case consisting of a pH glass electrode and a separated reference electrode. The use of divided electrodes minimises the aging process of conventional pH electrodes, which is primarily related to the reference electrode, and thus is an important requirement for the long-term use in soils. Together with the related measuring electronic, the ecoTech pH electrode for soil application was registered as invention (at the German patent office) (‘Online-Messsystem für pH Werte in Böden, Patent DE202009014978) on April 2010.
From 2008 to 2015, the structure of the electrode was continuously optimised and adapted to new findings. An in-depth examination of the electrode for the laboratory use was conducted in close cooperation with the University of Trier, the results have been published by Thiele-Bruhn et al. 2015. The electrode is specially designed for a long-term, stationary use in soils, even under water saturated conditions. Due to its small dimensions (D = 6 mm) is also suitable for the use in laboratory soil columns. For field use a protective sleeve is available, which can be extended by extensions to lengths of more than 1 m. Field trials with long-term installed pH electrodes have been running since April 2014, and since May 2014 the Geological Survey of North Rhine-Westphalia publishes his measured daily values on their own homepage: ([German] http://bodendesjahres130.apps-1and1.net/staumeldungen/redoxpotenzial-ph-wert/).
As reference electrode for the pH electrode, an Ag/AgCl-reference electrode is used, which is connected to the pH electrode via a salt bridge. The measured values can be read out stationary using our especially developed connection module (4611) for pH and redox measurement in combination with a suitable SDI12 data logger. Here, any pairing of pH and redox electrodes is possible, in total up to 7 units can be hosted per module. For larger electrode numbers per field site or laboratory experiment, additional modules (4611) can be connected. Their parallel and serial operation is possible. Using the same measuring system, the values of pH and redox electrodes (Item no. 461) can be read and logged in the laboratory and the field as well. The pH electrode was tested down to temperatures of -18°C without damage and is therefore regarded as frost-proof.
|Measuring range:||-175 to +175 mV
pH 4 to pH 10
|Connection Module Output:||SDI-12|
|Shaft diameter:||6 mm|
|Shaft length:||80 mm|
|Cable length (standard):||3 m|