Analyzer System Performance Flashcards
Which type of analyzer error causes unpredictable scatter in the readings?
Random error
When is it necessary to use the Student’s t values for calculation of confidence intervals?
For a sample size that is less than 32
What can be done to help reduce systematic error?
Systematic errors can be calibrated out
What sources of random error could affect an analyzer system?
1) Process noise
2) Ambient temperature change
3) Pressure fluctuations
4) Calibration standard accuracy drift
Once an uncertainty range of an analyzer is found what can it be used for?
It can be used to set alarms and compare with lab results
Describe determinate VS indeterminate systems
Determinate systems have defined limits while the indeterminate systems do not
What is the term that describes the sensors output response?
Sensitivity
What is the term that describes things other than the chemical of interest that cause an
output from the sensor?
Interference
What 3 things is sensor’s output made up of?
1) Sensor’s response to chemical of interest
2) Interference
3) Electrical noise
Describe the three sources of electrical noise affecting analyzer sensors and give one design
element that is used to avoid/reduce each
1) Thermal: occurs due to thermally induced motion of charge carriers. This can be reduced by keeping the detector cool or reducing the bandwidth reaching the detector
2) Flicker: noise that affects all electronic devices. Can be prevented with electronic or physical chopping.
3) Environmental: occurs due to transfer of energy from the surroundings into the measurement system. Proper grounding and shielding techniques get rid of this issue.
How could you estimate the amount of noise affecting a sensor?
Measure the standard zero and determine the standard deviation of the readings from the sample.
In control charts used for monitoring analyzer data quality, how many standard
deviations above the mean is the upper control limit?
3
Give an example of one method for minimizing the impact of noise on a sensor’s signal.
1) Electronic filtering
2) Lock-in or tuned amplification
3) Signal integration
How is analyzer response time usually determined?
Response time is measured by switching between two different standards and monitoring delay
When is an analyzer considered to be “in control”?
When all sample points fall between UCL and LCL and the pattern is random
