Permanent Portable Reference Electrode Model IT
EDI’s permanent portable reference electrode, Model IT, is used to make potential readings in any application where a standard, liquid-junction portable reference electrode is presently being used. The Model IT contains a gel rather than a liquid so it can be used in all positions. The gel provides long maintenance-free service since it does not require refilling or cleaning. Soil contact is through a hardwood plug which offers several advantages over ceramic membranes: it will not clog as readily, it is resistant to salt blockage, and it can be reworked by light sanding or cutting if it becomes contaminated with oil. The Model IT has a twenty year design life and an indefinite shelf life if the end cap is in place. Gelled copper/copper sulfate (CUG) electrodes have a blue housing while gelled silver/silver chloride (AGG) electrodes have a light grey housing. Refer to the sidebar for additional information on these elements. Both models have a 1/4 – 20 threaded stud termination.
The Model IT can be ordered with a temperature indicator which is bonded to the Model IT electrode body. The indicator displays the electrode body temperature in increments of 1°F over the range of 26°F to 120°F. This can be important because the reference potential of an electrode is affected by its temperature. Some of the newer standard practices now encourage the user to record the electrode’s temperature at the time of the reading so that adjustments can be made if necessary. A second option is the addition of antifreeze added to the gel so that the electrode will not be damaged if exposed to temperatures down to -30°F (-34°C). However, antifreeze may shift the reference potential by up to 12 mV.
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Element Selection Guide
EDI reference electrodes may be ordered with any of five different reference elements. The element selected depends upon the electrolyte in which the electrode is used.
Gelled copper/copper sulfate elements (EDI code CUG) are typically used in environments with less than 500 ppm chloride or other halides. They consist of high purity metallic copper immersed in a saturated CuSO4 solution containing a gelling agent. Use of these elements in electrolytes with higher halide levels or in electrolytes with any sulfides present will contaminate the element causing its reference potential to drift. Because of their widespread use, Cu/CuSO4 electrodes are the ones upon which many cathodic protection criteria are based. Cu/CuSO4 elements are available in all EDI product groups except Concrete Products.
Gelled silver/silver chloride elements (EDI code AGG) can be used in any environment which does not contain sulfides. They consist of 99.99% pure silver coated with silver chloride and immersed in a saturated potassium chloride solution containing a gelling agent. The reference potential of Ag/AgCl/sat. KCl elements is 105 mV negative to that of a saturated Cu/CuSO4 reference electrode. Ag/AgCl/sat. KCl elements are available in all EDI product groups.
Dry silver/silver chloride elements (EDI code AGD) are most commonly used in clean full strength seawater where the electrolyte comes into direct contact with the element. Like the gelled Ag/AgCl elements, they are adversely affected by sulfides. The reference potential of dry Ag/AgCl elements immersed in full strength seawater is 70 mV negative to that of a saturated Cu/CuSO4 reference electrode. As the ambient chloride level decreases, as would be the case when used in brackish water, the reference potential becomes less positive. Dry Ag/AgCl elements are only available in our through-wall, immersion and tubesheet mounted reference electrodes.
Dry silver/silver chloride elements for concrete (EDI code AGC) is a variation of our standard dry Ag/AgCl element which has been adapted for encasement in a cement-based grout. The reference potential depends on the pore water chloride level of the concrete structure in which it is embedded. This element is only available in our Marine Concrete reference electrode, EDI Model CM-AGC.
Zinc elements (EDI code ZIN) consist of high purity metallic zinc rod. When these elements are used in our underground reference electrodes, the zinc element is encased in a gypsum-bentonite backfill. The zinc element is directly wetted by the electrolyte in our through-wall and immersion reference groups. Reference potential of a zinc element encapsulated in backfill is about 1,100 mV negative to that of a saturated Cu/CuSO4 reference electrode. The reference potential of zinc directly exposed to an electrolyte depends on the composition of the electrolyte.
Design Life
The design life of a reference electrode is an estimate of the time based on test results it would take for enough salt to diffuse out from the inner core to lower the salt concentration to below saturation. At EDI, we use several techniques to extend this time as much as possible. One of these techniques is to increase the amount of salt reserve contained in the gel. This is one reason why longer life electrodes have physically bigger housings. Download our paper Factors Affecting the Accuracy of Reference Electrodes to learn more.
For More Information
Complete Product Information is available for downloading as pdf files. Click on the link below to download.
Permanent Portable Reference Electrode (Model IT) data sheet.
Order form with web discount (ORDER FORM).