Normal Size Small Size show me how
|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.
|Temp. sensor. Exhibits the largest resistance change w.r.t change in temp.
|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.
|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
|A comparison b/t a standard and what we want to measure (the measured).
|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).
|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.
|Converts the sensed information into a detectable signal
|Modifies (amplification, filtering) the signal for the final stage.
|A variable that can be changed independent of other variables. They do not affect its value.
|A variable that IS affected by a change in other variables.
|Analog- Varies Smoothly, continuous (glass thermometer) Digital- Varies in a step-wise manner Example: Thermometer with a digital display.
|Constant with respect to time, easily read with analog display. -Glass thermometer -Tire Gages
|Varies w.r.t. time. Typically read with a measuring system with recording capabilities.
|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.
|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.
|A way of ensuring that all the various test possibilities were obtained.
|The difference between the highest and lowest values in the set.
|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
|The closeness of a measurement (or a set of observations) to the true value.
|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.
|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.
|Errors that are produced due to the fact that hysteresis is present
|Deviations from linear behavior. This can be calculated.
|Zero Shift (null) Error
|Variation in the linearity parameter a0. Sensitive to temperature fluctuations.
|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
|Variation in the linearity parameter a1. Sensitive to temperature fluctuations.
|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.
|A likely bound on the error or a part or measurement. Uncertainty is dictated by application.
|A measure of the random variation found during repeated measurements.
|The difference between the average and true values
|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
|The basic quantity being measured
|*Control of a variable
|Holding a variable to a prescribed value during an experiment.