Chemical Processing - July 2008 - (Page 36)

Double junction reference pH sensor Figure 4. This design is better able to contend with sulﬁde and cyanide ions. e main components of a typical pH loop are the process, sensor, cable and transmitter. ese, individually or in combination, can produce problems with measurements. A ﬁve-step approach can help pinpoint the source: 1. Identify the problem. Recognizing there may be a problem with a measurement signal is the start of troubleshooting. Process knowledge, measurement history and data trending are key factors in determining if the pH reading is correct. 2. Isolate the problem. In some cases, the application may be the problem. Process conditions play an important role in successful pH measurement. For example, low conductivity water will require a special reference. If the process is associated with sterilization cycles, PTFE may not be a suitable reference junclow electrical conductance. To overcome this sitution. Frequent replacement can be a tip-oﬀreference ation requires applying external sources of electroSilver/Silver chloride + to use of the wrong sensor. Always document lyte to the sensor — reference electrolyte is supplied Potassium chloride process conditions. from an external reservoir into the reference cell. 3. Find -the culprit component. With one complete working pH loop, interchange components in Reference junction + the order of sensor, cable and transmitter to isolate the problem part of the pH loop. 4. Characterize the problem. If you’ve identiﬁed the + sensor as the issue, check the area around the FOR SEALED ELECTRICAL PANELS Ion cloud - junction. Inspect the measuring glass. reference + + THE COMPACT See if there’s any discoloration of the reference + ﬂuid. Occasionally a pH sensor can pass quality7.0 Inernal buffer CABINET COOLER control testing at the factory and the perforREMOVES WASTE HEAT + mance test at the customer’s site but ultimately WHILE KEEPING OUT Glass membrane suﬀer a short life. CONTAMINANTS USING 5. Check for galvanic isolation — ground loop. + HEAT PIPE TECHNOLOGY!! Use H procedure mentioned earlier. A posthe sible ﬁ x to the ground loop may be as simple Maintenance Free as removing the output wires from the transEasy as a fan to install NEMA 12 Much lower energy costs mitter (for example, the 4–20 mA output) TROUBLESHOOTING PH SENSORS EFFICIENT COOLING + Flush Mount Hazardous location units NEMA 12, 3R, 4, 4X Many models are in stock Stainless Steel and Washdown UL, cUL, and RoHS compliant Operating costs are a fraction of air-conditioning NEMA 4X Stainless Steel Digital signal inductive data inductive transmission of energy www.norenproducts.com (866) 936 - 6736 (650) 322 - 9500 Figure 5. This unit uses an inductive coupling between sensor and cable, and avoids problems with galvanic interference. http://www.norenproducts.com http://www.norenproducts.com

Table of Contents Feed for the Digital Edition of Chemical Processing - July 2008

Chemical Processing - July 2008 Contents From the Editor ChemicalProcessing.com Field Notes In Process Energy Saver Compliance Advisor Who’s a Big Hit? Succeed with Condensate Control Take Some Basic Steps with pH Measurements Steam Projects Provide Fast Payback Process Puzzler Plant InSites Equipment & Services Product Spotlight/Classifieds/Ad-Lits Ad Index End Point

Chemical Processing - July 2008

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