Sampling Systems Part B Flashcards
What is a grab sample?
Small portion of material removed either manually or automatically out of a process
What is a representative sample?
A sample that has the same composition as the process
Where should sample extraction probes be inserted into a pipeline?
Center third area of the pipe where fast flow is present and the process is mixed
Grab sample containers must be _____________ so they do not react chemically with the sample and
change its concentration.
Inert
A _____________________ should be left in the cylinder when transporting volatile liquids in order to
allow room for liquids to _______________________.
Vapour space, expand
Floating piston cylinders allow for safely taking and maintaining samples of liquids and gases at
____________ ________________.
Pipeline pressure
What is a composite sample? How could you take a composite sample?
A sample that is made up of smaller samples taken over time. This is done using an automated sampler that takes samples at certain timed intervals.
Rank in situ, at-line, and distant sensors in order of responsiveness. Which type of sensor placement is
best for direct process control?
In-situ: best for direct process control as it has a rapid response
At-line: analyzer does not control an FCE and can withstand longer lag times
Distant: longest lag time
What is the maximum sample conditioning time?
30 seconds
What are 4 reasonable ways that total system lag time can be decreased?
1) Decrease volume by decreasing tubing diameter
2) Decrease dead space by decreasing the number of conditioning devices
3) Increase flow rates
4) Decrease tubing length
True/False: The sample return point should be at higher pressure that the sample point
False, the sample return is at a lower pressure
True/False: A fast loop is used when the sample has to travel a long distance to the analyzer
True
The number one priority of sampling system design is _____________________.
Safety
Another priority of sampling systems is to ensure that a _______________________ sample is extracted
and provided to the analyzer.
Representative
What is the purpose of installing block valves in a sample system?
Isolate the sample for maintenance work
What is a dead space or dead leg? How can you avoid them in your sampling system?
Parts of the inner volume of the sample system that remain static and are not continuously swept by the flow of the system. To avoid this 4-way selector valves may be introduced.
Name a style of system that prevents cross-contamination for multi-stream switching applications.
Double block and bleed switching system
True/False:A sample system that contains a vapour sample should always be kept below the vapour’s dew point.
False, should be kept above dew point to make sure the sample doesn’t condense.
True/False: A sample system containing a low-boiling liquid should be kept at a pressure above the liquid’s vapour pressure for that specific temperature.
True
What conditions can cause gas samples to change composition after extraction from the process line? How can this be prevented?
If the temperature of the gas is close to its dew point. Reducing the pressure or increase the temperature to prevents this from happening.
What conditions can cause liquid samples to change composition after extraction from the process line? How can this be prevented?
Change of temperature or pressure in the sample.
How can you check for blocked filters without removing the filter?
Pressure gauges can be installed before and after a filter to check it without removing the filter.
