Local instrumentation and control specialist Endress+Hauser has released a new double junction electrode pH probe that offers both extended product life in applications with 'poisonous' substances as well as an IP68 connector for the pH probe and cable to alleviate historical connection problems.
Endress+Hauser has had its CPF81 pH probe as part of its analytical product basket for some time. Similar to other combination probes, the CPF81 consists of a measuring electrode - a standard electrode with a glass sensitive bulb through which the hydrogen ions migrate - and a reference electrode. However, this is where the similarity ends, as the CPF81's reference electrode is made up of two compartments separated by a Teflon diaphragm. The primary diaphragm is three times as thick as a standard diaphragm, which makes 'poison' intrusion into the electrode very difficult, while the secondary diaphragm that seals the reference electrode further hampers the 'poison' migration. The compartment between the primary and secondary diaphragm is filled with potassium nitrate, and acts as a 'poison' trap to catch any poisons that have migrated through the primary diaphragm. In this trap, the 'poison' reacts with potassium nitrate, forming various complex chemical compounds. Extended exposure of the potassium nitrate to poisoning agents will eventually deplete it, but during this time, the reference chamber remains untouched and constant at pH 7.00, and with a potassium chloride concentration of 3 mol. Only when the poisons have migrated through the secondary diaphragm and start to contaminate the reference, is probe replacement necessary.
In the wastewater industry, many poisons such as cyanides, hydrogen sulphide and sulphites are present which contaminate pH probes and necessitate their frequent replacement, resulting in unplanned direct costs, as well as indirect costs such as downtime and loss of productivity. The wastewater double junction electrode probe from Endress+Hauser is an established product, but is further enhanced by the addition of the TOP68 connection head.
For accurate pH measurement, an accurate connection between the probe and cable is required. Fixed cable probes are difficult to insert and replace for calibration due to the wind up of the cable, while separate cable and probe assemblies are very sensitive to moisture intrusion. Should moisture penetrate the connection, both cable and probe have to be discarded since the connection cannot be dried out. The main reason is that the pH signal requires a high impedance connection to transmit the millivolt signal. To overcome this electromechanical problem, Endress+Hauser has developed an IP68 TOP68 connector for their probes. The connector base material is made of a hydrophobic material, PFA, resulting in a water repelling action which ensures that should moisture occur inside the connection, the base material does not absorb it. This is all encapsulated in PPS that is temperature shock and chemical resistant. The connector was placed under stringent tests to ensure that it complies with all the rules and regulations of the IP68 standard, and is autoclavable, sterilisable and waterproof.
The combination of double junction electrode pH probe and an IP68 connector offers the best of both worlds, giving the customer both chemical and mechanical protection against everyday problems in pH measurement.
| Tel: | +27 11 262 8000 |
| Email: | [email protected] |
| www: | www.endress.com |
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