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Frequent calibrations are often a necessary evil in the world of analytical measurements and analyzers. Accurate measurements are non-negotiable for safety and effective process control. However, the expense and complexity of frequent calibrations can pose significant challenges. Thankfully, ZEGAZ Instruments' dew point analyzers offer a unique advantage – they eliminate the need for core measurement calibration. Before delving into this, it's important to explore the challenges associated with calibration in other methods.
Why Calibration Is Necessary
Calibrations are necessary because most gas sensors (and sensors in general) suffer from drift problems. Depending on the sensor, there can be many reasons for drift. Some drift problems can be addressed through calibration, and some cannot be. Calibration is used as a tool to adjust for the drift issues in the sensors.
Calibrations have a cost. Frequent calibrations are a major issue for most analytical measurements and analyzers, particularly in the gas industry. Many instruments require calibration 2-3 times a year, even more if the gas isn't exceptionally clean. While on-site calibration is more cost-effective, sending equipment back to the factory for calibration can cause significant costs, especially if it involves international shipping, calibration fees, and extensive paperwork.
On average, calibration may cost about 15% of the purchase price per year (excluding down- time and the cost of inaccurate measurements). However, for some moisture sensors, such as aluminum oxide sensors, the raw calibration cost can be much more. It’s not a surprise that these challenges have even led some customers to opt for purchasing new analyzers rather than enduring the cost and hassle of sending old ones for calibration.
The Troubles with Measurements:
Now, let's delve into why calibration is crucial in some gas analyzers:
Aluminum Oxide Sensors
Consider moisture measurement using an aluminum oxide sensor. This method requires a series of assumptions to function correctly that are barely true in the world of natural gas measurements. Each assumption and measurement process, discussed thoroughly before, introduces uncertainty. These uncertainties compound, leading to a big margin of error, increased costs, extensive timeline, far larger than anticipated.
Traditional Chilled-Mirror
Chilled mirror measurement is also another widely used method for measurement of moisture in natural gas. In a chilled-mirror measurement, a surface is cooled until condensation is detected, and the temperature at which this condensation occurs is recognized as the dew point. Given that this is a first-principle method, in general it has much lower sources of error and uncertainty. Since there is only a temperature sensor in play, and since temperature sensors are very mature and drift free devices, the chilled-mirror devices typically do not need calibration. The main challenge in chilled-mirror devices is distinguishing between moisture and hydrocarbon dew points. This challenge has been effectively addressed by the use of CEIRS™ technology introduced by ZEGAZ INstruments.
Quartz-Crystal Monitor
Quartz-Crystal Monitors (QCM) is another tool that is used for measurement of moisture content in natural gas. While this is a very effective tool for measurement of moisture in very clean gas streams (such as ultra-pure industrial gasses), it is a poor choice for measurement of moisture in natural gas.
QCM sensors are essentially a microbalance, a very small and sensitive weight balance. Under ideal conditions, they can measure the weight of anything (ideally but not practically only moisture) on an oscillating crystal. Changes in the oscillation frequency are correlated, with the weight of the material on the crystal, and that weight is correlated with the vapor pressure of the crystal.
It is very easy to see what can go wrong or drift. In natural gas, there may be other things that get absorbed on top of the crystal causing drift. Oscillating frequency of crystals is also temperature dependent, so there needs to be some compensation for it. The absorptivity of the material (hygroscopic) on the crystal will change over time causing another source of drift.
This problem is addressed in some instruments by circulating dry gas through the unit at every cycle. This is typically referred to as zeroing of the instrument. While this is a band-aid and addresses the zero problem, it does nothing to address the measurements through the full dynamic range of the instruments. This also means that there needs to be a source of dry gas, or dryers for the instrument to use.
The ZEGAZ Difference: No Calibration Needed
ZEGAZ Instruments' line of dew point analyzers breaks free from the need for frequent calibration, offering a cost-effective alternative. These analyzers are fundamentally advanced automated chilled mirrors, providing precise measurements without the hassle of regular calibration.
ZEGAZ Instruments' chilled-mirror analyzers rely on a spectroscopic method that remains immune to such issues. ZEGAZ Instruments uses infrared beams for unambiguous condensation detection. Moreover, the temperature sensor, the primary element requiring calibration, is a small thermistor that holds its calibration indefinitely since it remains isolated from air and moisture. The exposed surface in ZEGAZ Instruments' analyzers is a highly inert ceramic that resists degradation even in harsh environments. As a result, no calibration is needed for the sensor, offering significant savings over time.
Years of data and real-world experience confirm the effectiveness of ZEGAZ Instruments' approach. None of their instruments have lost their original calibration, and the inert ceramic surfaces remain unaffected, making ZEGAZ's analyzers a cost-effective and reliable solution for accurate gas measurements.
With ZEGAZ Instruments, you can navigate the analyzer costs and sidestep the frequent calibration headaches, benefiting from accurate measurements without the recurring expense.
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