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FirstQuiz

341

QuestionAnswer
Thermocouple Two wires of different metals. Voltage gradient is produced due to a difference in temperature at two junctions allowing for one to create a correlation b/t voltage and temperature difference. Many types based on the alloys used.
Thermistor Temp. sensor. Exhibits the largest resistance change w.r.t change in temp.
RTD Temperature sensor PTC (resistance increases w/ temp. increase) Made of platinum, nickel, or copper Correlates resistance with to temperature Used infrequently
Cold Junction Compensation A temperature sensor is placed next to the RJ. Add this to the gradient picked up by the thermocouple, and an abosolute temperature at the measurement junction can be found.
Thermocouple "types" Refer to the different standardized alloy pairs of thermocouple wires (alloy pairs because, remember, we have two wires connected at a common junction). The different alloying pairs allow for different functionalities amongst the thermoucples.
PTC thermistors vs. NTC thermistors PTC-resistance increases with increasing temperature. NTC- resistance decreases with increasing temperature
Measurement A comparison b/t a standard and what we want to measure (the measured).
Standard Something considered by an authority as a basis of comparison. Other parameters can be defined in terms of these standard parameters (velocity=length/time, where length and time already have established parameters).
Sensor Uses a natural phenomenon to sense the variable being measured (thermometers, thermocouples, etc.). It measures this variable (often a physical quantity) and converts it into a signal which can be read by an observer or an instrument.
Transducer Converts the sensed information into a detectable signal
Signal Conditioning Modifies (amplification, filtering) the signal for the final stage.
Independent Variables A variable that can be changed independent of other variables. They do not affect its value.
Dependent Variables A variable that IS affected by a change in other variables.
Analog/Digital Analog- Varies Smoothly, continuous (glass thermometer) Digital- Varies in a step-wise manner Example: Thermometer with a digital display.
Static Signal Constant with respect to time, easily read with analog display. -Glass thermometer -Tire Gages
Dynamic Signal Varies w.r.t. time. Typically read with a measuring system with recording capabilities.
Noise/interference Noise- Random variation in output due to of extraneous factors such as environment or temperature. Static from radio. Interference- Produces unwanted deterministic trends from extraneous variables.
Hysteresis When a graph does not act the same on the way up as it does on the way down. Difference b/t the upscale and the downscale.
Repetitions vs. Replication Repetition- Repeated measurements made during any single test or on a single batch. Replication- An independent duplication of a set of measurements using similar operating conditions.
Test Matrix A way of ensuring that all the various test possibilities were obtained.
Range The difference between the highest and lowest values in the set.
Sensitivity The change in the output per unit change in the input. Determines the useful range. In the case of a linear calibration curve the slope of the line is called the static sensitivity
Accuracy The closeness of a measurement (or a set of observations) to the true value.
Precision The closeness of multiple observations or repeatability of a measurement. Refers to how close a set of measurements are to each other. It can often tell you if your experimental set-up produces repeatable results.
Calibration A measurement of performance of an instrument or sensor to ensure accuracy for future measurements. Done by applying a known value of input to a measurement system, and then observing the systems output.
Hysteresis Error Errors that are produced due to the fact that hysteresis is present
Linearity Error Deviations from linear behavior. This can be calculated.
Zero Shift (null) Error Variation in the linearity parameter a0. Sensitive to temperature fluctuations.
(Instrument) Repeatability The measure of the variation that occurs when a sensor is repeatedly calibrated under identical conditions. This is normally described by the Standard Deviation, Sx, of the data
Sensitivity Error Variation in the linearity parameter a1. Sensitive to temperature fluctuations.
*Calibration Curve Obtained by plotting the output vs. the input. This also determines the useful range within which the instrument/sensor/system can be used.
*Resolution (of a sensor) The minimum detectable signal fluctuation.
*Absolute Error =true-indicated value
*%Accuracy (1-(abs[absolute error]/true)*100
*Uncertainty A likely bound on the error or a part or measurement. Uncertainty is dictated by application.
*Precision Error A measure of the random variation found during repeated measurements.
Bias Error The difference between the average and true values
*Linearity yl(x)=a0+a1x -> Many types of sensors have linear input/output behavior, at least in some range. That region follows the equation above. The only calibration you will often get are: a1- the slope of the input/output relation a0- the zero input value
Variable The basic quantity being measured
*Control of a variable Holding a variable to a prescribed value during an experiment.
Created by: NoodlesNoodles