Why use Portable Measurements?
There are times when pipeline operators need to spot check oxygen levels at multiple locations. These sites may not have an Oxygen Analyzer installed, or they may require a second unit to verify that an existing reading is correct. The sites may even be located far from one another, requiring considerable driving time to carry out measurements. When confronted with this situation, an Oxygen Analyzer with portability affords not only quick measurements but also much-needed convenience.
Types of Portable Oxygen Analyzers
Portable Oxygen Analyzers are categorized by their measurement capability.
Trace Oxygen Analyzers
Extremely accurate O2 measurements down to low ppm levels. Typically selected when target oxygen level is between 0.5 and 10,000 ppm. They will still measure higher O2 levels up to 100% but the sensors are optimized for trace levels of oxygen.
Percent Oxygen Analyzers
Provide reliable measurements between 1% and 100% oxygen. Typically percent O2 analyzers are configured for the target range of oxygen expected in the gas stream.
Analyzer Design – Things to Look For
There are many Portable Oxygen Analyzers to choose from, and their designs can be vastly different. In selecting an Analyzer, operators should not only consider the reliability of the readings but whether the unit can provide the necessary ease of use, protection and ruggedness to handle the physical demands of field work.
Flow efficiency of the sensor pocket is a key factor in how fast the Analyzer can respond to the sample gas. A good design will allow a rapid and full purge of the sensor pocket. This will allow the sensor to respond quickly and detect any changes in the sample gas. In contrast, a poorly design pocket can have a ‘blind cavity’ that limits the exposure of the sensor to the sample gas and create ‘dead legs’. This will slow the exit of ‘previous sample gas’ from the sensor area. Therefore, for quick, reliable measurements on the go, make sure your Portable O2 Analyzer contains a properly designed sensor pocket.
Additionally, the presence of residual air in the sample lines can cause the Analyzer’s readings to spike after the initial connection to the Sample Tap. The long ‘come down’ time will delay getting a proper measurement of the sample, and the postponement will cascade with all subsequent measurements at other sites. But this can be avoided if the Analyzer design provides a bypass of the oxygen sensor. An example is seen on the Portable Oxygen Analyzer from AMI. Its 4-way valve, part of the ELIMINATOR CELL BLOCK™, allows the user to fully purge air from the sample lines with process gas while simultaneously bypassing the oxygen sensor.
Protection for the Oxygen Sensor
Unlike a permanent mount Oxygen Analyzer which continuously measures the content of the sample gas, a Portable Analyzer is used primarily for spot-checking. Because the oxygen sensor is not always in use, it is prudent to avoid exposing it to air – as this unnecessarily results in a long come down time and reduces the life of the sensor.
Though most units do not contain a solution in their design, AMI provides a creative solution for its line of Portable Oxygen Analyzers. The 4-way Selector Valve, part of the ELMINATOR CELL BLOCK™, allows the user to isolate the sensor from the sample gas path by a quick, simple turn. This protects the oxygen sensor while the Analyzer is moved between measurement sites.
Tough Design & Durability
Any Portable Analyzer will experience constant ‘wear and tear’ from being moved around, connecting to and disconnecting from the Sample Tap and even being accidently dropped. The unit may also be exposed to some of the harshest regions, including those with extreme temperatures. For the Analyzer to withstand these environments, its design must be extremely tough and rugged – not only to protect the unit but also the reliability of its measurements. This means the materials used in its construction, as well as its fittings, must have the proper ratings and passed endurance testing. And the Sample System should not contain potential leak points that are vulnerable to sudden impact or force that could compromise the integrity of the sample gas path.
The availability of accessories can make measurements far easier for a Portable Oxygen Analyzer as well as extend its life. For example, flexible high-pressure sample tubing is great to have when connecting the Analyzer to a pressurized sample line. Additionally, in situations when the line has no positive pressure, a portable sample pump is a necessity to move sample gas into the Analyzer. Last, transporting the unit in a proper carrying case will provide it with some added protection.