Optical fiber pH sensors for high temperature water. Final report
The goal of this program was the development of an optical pH measurement system capable of operating in a high-temperature aqueous environment. This project built upon a dual-wavelength fiber optic sensing system previously developed by Research International which utilizes light-emitting diodes as light sources and provides remote absorption spectroscopy via a single bidirectional optical fiber. Suitable materials for constructing an optical pH sensing element were identified during the program. These included a sapphire/Ti/Pt/Au thin-film reflector, quartz and sapphire waveguides, a poly(benzimidazole) matrix, and an azo chromophore indicator. By a suitable combination of these design elements, it appears possible to optically measure pH in aqueous systems up to a temperature of about 150{degrees}C. A pH sensing system capable of operating in high-purity, low-conductivity water was built using quasi-evanescent wave sensing techniques. The sensing element incorporated a novel, mixed cellulose/cellulose acetate waveguide to which an azo indicator was bound. Testing revealed that the system could reproducibly respond to pH changes arising from 1 ppm differences in the morpholine content of low-conductivity water without influencing the measurement. The sensing system was stable for 150 hrs at room temperature, and no loss or degradation of the pH-responsive optical indicator was seen in 160 hrs at 50{degrees}C. However, the prototype polymer waveguide lost transparency at 1.7% per day during this same 50{degrees}C test. Additional effort is warranted in the areas of water-compatible waveguides and evanescent-wave detection methods.
- Research Organization:
- Electric Power Research Inst., Palo Alto, CA (United States); Research International, Inc., Woodinville, WA (United States)
- Sponsoring Organization:
- Electric Power Research Inst., Palo Alto, CA (United States)
- OSTI ID:
- 10102601
- Report Number(s):
- EPRI-TR-104196; ON: UN95004479; TRN: 95:000160
- Resource Relation:
- Other Information: PBD: Nov 1994
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
47 OTHER INSTRUMENTATION
FOSSIL-FUEL POWER PLANTS
ON-LINE MEASUREMENT SYSTEMS
WATER CHEMISTRY
COOLANTS
PH VALUE
MONITORING
MORPHOLINES
TEMPERATURE RANGE 0273-0400 K
OPTICAL SYSTEMS
MEASURING INSTRUMENTS
BENZIMIDAZOLES
HIGH PRESSURE
200104
440800
COMPONENTS
MISCELLANEOUS INSTRUMENTATION