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SIGRIST Oil in Water Monitors have been proved in the following applications:
- Monitoring of oil seperators on tankers, platforms, docks, etc.
- Monitoring of heat exchanger cooling water for oil leakage
by measuring fluorescence in a free-falling sample stream.
Instrument Features
- non-contact measurement in free-falling flow cell
- minimum maintenance
- easy adjustment with solid reference
- high stability by dual-beam method
- sturdy design even for harsh environments
- EEx-p version in stainless steel cabinet
- Exprotection EEx-p IIc T4
- User-specific calibration to as many as eight oil grades
Non Fouling Sample Cell
SIGRIST presented the first oil trace monitor performing a non-contact measurement in a free-falling sample stream years ago. Due to the absence of windows in contact with the sample, window fouling is eliminated once and for all. High temperature samples up to 95°C can be measured with an optional purge air injector. The result is a maintenance-free sample cell proved in various platform applications.
Characteristics of the Monitor
Uncompromising in design and workmanship:
- Easy to service: no flow cell cleaning; no zero adjustment; easy adjustment check with solid reference
- Stable: No drift of the reading during adjustment interval due to dual-beam method. Using only one light source and one photodetector, all fluctuations and ageing effects of optical and electronical components are eliminated automatically
- Sturdy construction: contributes greatly to the high reliability and extremly long service life of SIGRIST instrumentation. SIGRIST photometers that have provided dependable service for over 50 years verify the quality of both design and workmanship
- EEx-p enclosure: especially developed for oil platform applications, a stainless steel cabinet containing oil trace monitor and control unit provides EEx-p certification and even improved environmental resistance of the system
Oil Detection by Fluorescence
The SIGRIST oil trace monitor is using the fluorescence measuring principle. If light entering a sample is transmitted to light with a longer wavelength, the phenomenon is called fluorescence. Many constituents of mineral oils possess the property of emitting visible light, when irradiated with UV light. This method is very useful for detecting traces of mineral oils in water or wastewater. The more intense the fluorescence light, the higher the concentration of the substance being measured.
The fluorescence method has two main advantages:
- Clear correlation between dispersed oil and PAH content measured by fluorescence
- The cross-sensitivity to solids is negligible
Calibration of Oil Trace Monitor
Standard factory calibration of SIGRIST oil trace monitors is done with a quinine sulfate solution with a concentration of 10 ppm giving a reading of 10 FLU (FLuorescence Units).
For oil concentration reading, the instrument has to be calibrated in addition to the particular oil. The reason is the difference in fluorescence intensity for the different oil types depending on their composition. In addition, the relation between oil concentration and quinine sulfate reading usually is not linear. A typical crude oil gives a reading of 20 FLU at a concentration of 80 mg/l.
This calibration on the particular oil to be measured can be done at site or at the factory. It is possible to calibrate the OilGuard with eight different oil samples.
Measuring Range and Sensitivity
The standard ranges for SIGRIST oil trace monitor are between 0 - 0,1 FLU and 0 - 100 FLU including automatic range switching possibility (1 FLU = 1 ppm quinine sulfate).
For many oils, these ranges make it possible, to monitor oil traces in the 0 - 100 ppm range very effectively and with a sensitivity in the sub-ppm range.
