871PH Series pH, ORP, and Fluoride Sensors and …

1 871PH SeriespH, ORP, and Fluoride Sensors and AccessoriesProduct SpecificationsPSS 6-1C2 A871PH multi-purpose precision electrochemical Sensors , used in conjunction with 871PH accessories , are suitable for pH, ORP, and Fluoride measurement applications. As symbolized by the CE marking, these Sensors conform to the European Union Sensors are used with 873 Electrochemical Analyzers, 870 ITPH Intelligent Transmitters, and 870PH Analog Transmitters. Measurement of pH by the Foxboro 871PH Sensors is accomplished by immersing a glass or metal electrode, with a reference electrode, into a process solution.

2 The glass or metal electrode produces an electrical potential proportional to the hydrogen ion activity. The reference electrode completes the circuit and provides a stable reference for the glass or metal electrode. These two electrodes constitute an electrolytic cell having a millivolt output that is proportional to the pH of the is related to the logarithm of the ratio of oxidation activity to reduction activity, just as pH is related to the logarithm of the hydrogen ion activity. A solution that contains an excess of oxidizing agent has a positive ORP while one containing an excess of reducing agent has a negative ORP applications include treatment of chromate and cyanide wastes produced by plating, chemical, and metal treatment plants.

3 ORP monitoring enables industry to determine reaction end points and to meet today's stringent environmental 6-1C2 APage 2 Fluoride measurement is accomplished by means of an ion-selective electrode, or ISE. A pH electrode is an example of an ISE which is sensitive to hydrogen ion activity. Similarly, the Fluoride electrode utilizes a lanthanum Fluoride crystal which is sensitive to Fluoride ion activity. When immersed in a solution containing free Fluoride ions, the electrode develops a millivolt potential proportional to the ion activity. Typical Fluoride applications include control and monitoring of fluoridation of drinking water MULTI-PURPOSE ASSEMBLYThis multi-purpose sensor assembly is suitable for virtually all process pH, ORP, and Fluoride measurement applications.

4 Its flexibility is further enhanced when used with a variety of mounting accessories . The sensor accepts a variety of glass pH, metallic pH, and ORP electrodes, as well as a new ion-selective electrode for Fluoride measurement. The unit is not affected by normally encountered chemical solutions and is capable of withstanding continuous operation in a wide range of process pressures and OF sensor BODYThe sensor assembly is available in either a Ryton or CPVC body. The Ryton body can be used in almost any normally encountered chemical solution, and is the preferred material where organic chemicals are present.

5 The CPVC body is used in applications involving hypochlorites or peroxides ( , bleach).CHOICE OF SENSING ELECTRODESG lass pH electrodes offer the best performance in most solutions and inherently provide the most accurate measurement. The flat ruggedized electrode or the small bulb results in a durable electrode suitable for industrial flat, ruggedized glass electrode with a Ryton body is recommended for most pH measurements because of its very durable, abrasion-resistant construction. This electrode is particularly resistant to wear, stress, and abuse caused by physical operating conditions.

6 Its optimum accuracy is in the range of 2 to 12 pH, although it can be used with Analyzers and Transmitters that are ranged from 0 to 14 spherical glass, low sodium error electrode with a Ryton body is recommended for applications where the pH is routinely in the range of 10 to 14 pH. It features a glass formulation with minimal sodium ion error. It should also be selected for applications in low conductivity water (down to 10 S/cm).Metallic (antimony) pH electrodes are available for abrasive solutions or for solutions containing hydrofluoric acid or other chemicals which attack glass.

7 Antimony electrodes should not be used in acid copper solutions nor in oxidizing or reducing solutions such as chromates, chlorine, hypochlorites, or or gold ORP electrodes are also available. (Gold is primarily used in cyanide reduction systems.)The newest addition to the 871PH 's electrode offering is an ion-selective electrode for the measurement of ppm Fluoride . The Fluoride electrode consists of a lanthanum Fluoride crystal in an epoxy body, and is compatible with the 873 DPX Analyzer and 870 ITPH DIAGNOSTICSWhen used with the Foxboro 870 ITPH Intelligent Transmitter, the intelligent configurations of the sensor (Model Code sensor Selections 3 , 4 , 5 , and 6 ) provide diagnostic information.

8 sensor health checks will reveal the following faults: Broken Glass Electrode Aging Glass Electrode Liquid Leakage into sensor Body Failure of High Impedance Amplifier in sensor ( sensor Selection Codes 3 and 4 only) Failure of Temperature Compensation Element Excessive Coating of the Reference ElectrodeFIELD INTERCHANGEABLE ELECTRODESI nterchangeable plug-in sensing electrodes are available to suit most applications. All electrodes are compatible with the same basic sensor body. If the measurement conditions or application needs change, it is simple to change from one measurement electrode to another in the REPLACEABLE REFERENCE JUNCTIONThe reference electrode is a nonflowing type.

9 A silver/silver chloride half cell immersed in saturated potassium chloride is used because of its highly stable output voltage. The filling solution and the ceramic junction may be readily replaced in the field. See Model Code section for choice of body PREAMPLIFIERAn integral preamplifier (Model Code sensor Selections 1 through 4 ) converts the high impedance pH signal to a low impedance signal, which is less prone to 6-1C2 APage 3 MOUNTING VERSATILITYThe basic sensor assembly may be mounted: In-line via Ball Valve Assembly In a sample line via Twist-Lock Flow Chambers In-line via Twist-Lock Bushings or Tees In-situ via Electrode Protection SleeveSee Physical Specifications section for additional AUTOMATIC TEMPERATURE COMPENSATIONA utomatic temperature compensation (ATC), utilizing a platinum resistance temperature detector (RTD), is a built-in feature in the 871PH OF ACCESSORIESA variety of process mounting accessories offers a versatile selection to meet virtually all process requirements (see accessories section).

10 PERFORMANCE SPECIFICATIONR eproducibilityTypically 2 mV dc ( pH unit) at reference conditions. Reproducibility at operating conditions depends on calibration standard used, cleanliness of electrode, and other process-related conditions. Optional Foxboro electrode cleaners aid in maintaining a high degree of reproducibility on pH and ORP electrodes in dirty process streams. (See PSS 6-1A2 C on Model ECS Electrode Cleaning Systems.)PRESSURE AND TEMPERATURE SPECIFICATIONSNOTER yton BodyCPVC BodyMaximum allowable temperature and pressure may be limited by installation hardware utilized.