| Term | Definition |
|---|
| The three types of error | Sampling, claibration, experimental bias |
| Noise | Unwanted fluxuations when measuring a static value |
| Why is it called static? | Derrived from radio engineering |
| What is RMS noise | the standard deviation of the noise |
| What goes on the denominator in SD calculations for a small sample set | n-1 |
| when is noise relevent? | when you know the amplitude of the signal |
| What is SEM | SD/ROOTn (n=no of experiments) |
| What does SD quantify | scatter |
| what does SEM quantify | \how accuratly you know the mean |
| What improves with increased no of experiments | SEM improves, SD does not |
| If scatter comes from experiment what should you repost? | SD should be reported |
| If the scatter arises from instrumental considerations what should be reported? | the SEM should be reported |
| What is sensitivity | signal/quantity, e.g. slope-signal/conc |
| Precision | % relative SD (RSD) |
| %RSD | Preciosn, noise/average signalx100% |
| limit of detection | the lowest signal you can see |
| what are T values dependant on | degrees of freedom (n-1) |
| What is the P value | probability of sampling N values and getting a mean as far from the hypothetical mean in your experiment |
| Name four examples of chemical noise | temperature, pressure, humidity and light levels |
| What is chemical noise | noise that arrives due to chemical properties |
| what is instrumental noise | any noise that is associated with the components of an instrument |
| what is white noise | Any type of noise that is indepedent |
| What is the other name for Thermal noise | Johnson noise |
| What causes thermal noise | arises due to the random motion of electrons in a resistive material - ususally caused by thermal agitiation |
| What does thermal noise cause | inhomogenities - which create voltage fluxuations (noise in resistors that cause a change in voltage) |
| What is bandpass | Related to the rise time of the instrument |
| How do you reduce thermal noise | lower the temp, use a smaller resistor, use a small bandpass (deltaF) |
| What does deltaF depend on | A range of frequencies but not the actual frequency itself |
| what is shot noise | random motion of charge carried across a junction |
| How can you reduce shot noise | Lower current, lower bandpass |
| The noise out of an amplifier... | is never going to be less than the noise in |
| When does flicker noise occur | at frequencies less than 100Hz |
| What causes flicker noise | drift in trnasistors |
| How do you avoid flicker noise | Increase working frequency to >100Hz |
| What is environmental noise | noise from interfernce or mechanical vibrations |
| Explain the cause of interfernce (line) noise | where a conductor acts nas an antenna and picks up the 60Hz noise from the wall |
| What is Stray capacitance | when two wires next to each other act as a stray capacitor |
| How do you avoid interfernce noise | Use elctrofrequency filters - nothc or high pass filter, and use properly sheilded wires |
| Where does mechanical vibrations originate | in the 10-20Hz range |
| What are particuarily prone to mechanical vibrations | Transistors are prone |
| what is quantitizing (bit) noise | Caused by rounding when converting from analog to digital |
| How can you improve quantitizing noise | by increasing the no of bits or use the full range of the convertor |
| What is a common way to improve signal to noise | by signal averaging ie the sum of many repetitions and take the average |
| to improve signal to noise by a factor of 4, how many samples do you need | x16 samples |
| What is required to apply sample averaging - signal | signal must be coherent ie n on random, and need a reference point at the start of the experiement, and the time jitter must be low |
| what is time jitter | how close the signals overlap with ref to time |
| what is required for the noise use sample averaging | stoicastic (totally random), no line noise (60Hz) and a guasian distribution of noise |
| When will sample averaging not improve | If the experiemnt suffers from line noise, 1/f noise, vibrational noise, ie anyhting that is not random |
| What is smoothing | taking the average of several popints together and replace them with a singal point representing the average value. |
| What is the purpose of smoothing | to reduce high frequency noise thats on a low frequency signal |
| What is the disadvantage of smooting | loose peak amplitude (peak height) |
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