BE 815

What are the three components required for uncertainty analysis?

1. Degrees of freedom of the standard deviation 2. standard deviation 3. systematic uncertainty

Stroboscopic Tachometer

A common laboratory device for measuring shaft speed is the stroboscopic tachometer, shown schematically in Figure 8.26. This device produces flashing light at a user-controlled frequency. This

True statements regarding correlation coefficients

A significant correlation coefficient means a strong linear relationship An insignificant correlation coefficient does not always mean an insignificant functional relationship An outlier can affect the correlation coefficient significantly

electric generator tachometer

A tachometer that has a small dc electric generator attached to the end of the shaft. the output of the generator will be a function of the shaft angular velocity

load cells

A transducer which converts force into a measurable electrical output.

Span

Algebraic difference between the upper and lower range limits of the input or output of a measurement device.

Leakage

Apparent false frequencies caused by effects at the beginning and end of the data sample

butterworth filters

Are maximally flat in the passband and have constant gain in the passband

high pass filter

Attenuates low-frequency energy but passes high-frequency energy

data acquisition system (DAS)

Automated system that takes data from measurement devices, processes them, then stores or records the data. Record signals at discrete times so there is no data between these times (digital ones)

Quantization Error

Basically another term for resolution error

multiple regression

Best-fit functions for situations with more than one independent variable.

Drift

Change in output of a measurement device over a set period of time due to several factors such as temperature or deterioration of components

Zero Drift

Change in the zero or null setting of an instrument over time.

Comparator

Circuit that compares two input voltage values and produces one of two possible output voltages, which identifies greater input value.

Sample-and-Hold device

Circuit used to acquire and store an analog voltage rapidly and accurately for use by other devices. (faster than A/D)

Accuracy

Closeness of the reading of an instrument to the actual quantity being measured. Usually expressed as ±percentage of full-scale output or reading. In instrumentation, usually includes only those errors caused by hysteresis, nonlinearity, and nonrepeatability.

Linearity

Closeness to which a calibration curve approximates a specified straight line. Linearity error is expressed as the maximum deviation of any portion of the calibration curve (average of upscale and downscale values) from a specified straight line.

Gage-amplifying-recording

Correct order for an electric signal measuring system

Elliptic filters

Crisp transition between the passband and stopband but allow ripples in both bands

Tachometer

Device for measuring the angular velocity of shafts

Potentiometer

Device in which the resistance varies as a function of linear or angular displacement

Digital encoder

Device that converts linear or angular displacement directly into a digital signal.

Venturi Tube

Device that measures fluid flow rate based on the principle of the Bernoulli equation applied to an area change in a conduit. Not easy to construct - expensive.

Flow Nozzle

Device that measures fluid flow rate based on the principle of the Bernoulli equation applied to an area change in a conduit

Pyrometer

Device that measures temperature by measuring thermal radiation (usually, high temperature values such as in a furnace environment).

signal conditioner

Device that modifies an electrical signal to make it more acceptable as an input to other devices. Functions include amplification, attenuation, filtering, differentiation, integration, converting voltage to current, and linearization

Pirani Vacuum Gage

Device used to determine vacuum pressures by sensing the gas thermal conductivity. Has a heat filament.

Linear Variable Differential Transformer (LVDT)

Device used to measure linear displacement by modifying and sensing the spatial distribution of an alternating magnetic field.

Error

Difference between the value indicated by the measurement system and the true value of the measurand being sensed

Hysteresis

Difference in output of the measurement system when the measurand is approached from higher and lower values

Operational Amplifier

Electronic amplifier with a high input impedance, low output impedance, and a very high low-frequency gain. ideal amp. has infinite input impedance and zero output impedance

Active filter

Electronic filter that combines passive elements, such as resistors and capacitors, wlth active elements, such as operational amplifiers.

Analog Multiplexer

Electronic switching device that can be used to connect any one of a set of inputs to a single output.

Resolution Error

Error due to imperfect resolution. Usually taken as one-half of the resolution.

confidence interval

Estimated interval containing a population parameter

Uncertainty

Estimation of error in a measurement or in a result, usually determined with a certain level of confidence (often 95 % ) .

Removing outliers that are two or three times the SD is good engineering practice

False

Alias Frequency

False frequency component that appears in the recorded signal when a signal is sampled at a frequency less than twice the maximum frequency in the signal.

bandpass filter

Filter that allows a selected range of frequencies to pass but attenuates frequencies outside the range selected

How to minimize conduction errors in gas-temp measurement using thermocouples

High convective heat transfer coefficient, long, thin probe, and low thermal conductivity of the probe

On outliers

If the data are nonlinear and small it is an ambiguous problem Outliers can sometimes be identified using standardized residual analysis experimenters are ultimately responsible for whether data points will be eliminated or used for analysis

Input Impedance

Impedance measured across the input terminals of an electrical device. Often frequency dependent.

Elemental uncertainties

Include uncertainty due to instability, quantization errors, data interpolation, and hysteresis

anemometer

Instrument for measuring or indicating the velocity of an airflow. Sometimes used in place of a velocimeter in the general sense.

Repeatability

Instrument's ability to produce the same output repeatedly under identical conditions.

McLeod Gauge

Manometric device used to measure vacuum pressures. Operating principle: a plunger compresses a large volume of low pressure gas into a smaller volume and then measures that pressure

Range

Measurand values, which a measurement device is intended to measure, specified by the upper and lower limits

Loading Error

Measurement error caused when the use of a measurement device changes the value of the measurement.

Spatial Error

Measurement error that occurs when a measurand (such as temperature) varies in a spatial region and an attempt is made to represent that variation with measurement in a limited number of locations.

current loop

Method of transmitting signals over wires in the form of a modulated current rather than voltage. Current-loop systems are less sensitive to noise pickup than voltage systems, and they are used to transmit data over long distances. (4-20 mA) signal accuracy not affected by voltage drop. Used widely for industrial process control

Digital signal transmission

Most reliable method travels very long distance

Bessel filters

Near linear variation of phase angle, is fourth order, and quite expensive.

Wheatstone Bridge

Network of four resistances, a voltage source, and a voltmeter used to measure the change in resistance of a sensor. Sometimes includes capacitors and is used to measure the change in capacitance of a sensor.

Measurand

Physical quantity, property, or condition that is measured.

Seebeck effect

Principle that describes how a low-level voltage is formed in a circuit by the junctions of two dissimilar metals when the junctions are held at different temperatures. It is the basis for the operation of thermocouples.

spectral analysis

Process of determining the component frequencies of a signal. Needs to identify the frequency characteristics of the measurand needed to determine sampling rate General time varying signal can be constructed of fourier-series

Analog-to-Digital Conversion

Process whereby an analog input signal is changed into a digital code.

piezoelectric

Property of certain materials (such as quartz) that generate electric charge when deformed, and vice versa.

Shielding

Protective covering that isolates a circuit or an electrical transmitting line from unwanted electromagnetic or radio-frequency interference.

Chebyshev filter

Provides a sharper roll-off value than butterworth filters at stopband frequency

Bandwidth

Range of frequencies over which a system will operate with close-to-constant gain.

Sampling Rate (Sampling Frequency)

Rate at which a signal is sampled (read) by a digital data acquisition system. expressed in Hz

Gain

Ratio between the output and the input of an electronic device such as an amplifier. Frequently expressed in a logarithmic form in decibels (dB).

Sensitivity

Ratio of change in the output to the change in the input of a measurement device.

Common temperature measurement errors

Recovery errors conduction errors radiation errors

signal attenuation

Reduction in signal amplitude that may be frequency dependent

Systematic Error

Repeatable error in a measurement that does not vary with replication. The same as bias error. It is estimated by the difference between the true value and average of a large number of readings.

Random Error

Same as precision error, a nonrepeatable error due to unknown or uncontrollable factors influencing the measurement.

Random Access Memory (RAM)

Semiconductor devices in a computer that can store digital data in a retrievable form. Data can be written to a particular location without having to sequence through previous locations. RAM is volatile, so all data are lost when the power is discontinued.

strain gauge

Sensor that converts a strain into an electrical signal. The most common type causes a change in resistance. Used as a sensor in pressure, force, and other measuring systems.

Areas where electrical sensing devices are advantageous to mechanical devices:

Signal conditioning, signal transmission, signal recording

Lowpass Filter

Signal filter that attenuates high-frequency signal components.

Resolution

Smallest detectable change in a measurement

Which probability distribution can be used for one-way ANOVA?

Student's T test

Calibration

Te st during which known measurand values are applied to the measurement device under specified conditions and the corresponding output readings are recorded.

Thermocouple

Temperature sensor consisting of the junction of two dissimilar metals. The output voltage produced is a function of the difference in temperature between the hot and cold junctions of the two metals.

Resistance Temperature Detector (RTD)

Temperature sensors based on the temperature effect on metal resistance. They are more accurate than thermocouples, and have an output response that is more linear. Have self heating problems.

Dynamic Error

The difference between a changing value and the momentary instrument reading or the controller action - associated with all instruments measuring time-varying measurands except those of zero order.

Zero order response

The ideal for a measurement system

Magnetic pickup transducer

The magnetic pickup is used in the distributor of many modern automobiles with electronic ignition to measure engine shaft speed and to time the spark. Magnetic pickups are also used as wheel angular speed sensors for automotive antilock braking systems.

Seebeck voltage

The sum of the peltier effect and the thompson effect

Central Limit Theorem

The theory that, as sample size increases, the distribution of sample means of size n, randomly selected, approaches a normal distribution.

Sampling Rate Theorem

Theorem which states that if a continuous signal is sampled with at least twice the frequency of its highest-frequency component, it can be fully recovered from the sampled data.

Photoelectric tachometer

They use photodetectors to measure angular velocity. Light beam shone on a perforated disk at one end and a photodetector at the other end. This detector creates a pulse output as the disk rotates. This is later converted into angular velocity. Only drawback is that oil and other contaminants may cover optical surfaces which lead to inaccurate output.

NDIR

This instrument is for measuring gas species, such as carbon monoxide, carbon dioxide, and sulfur dioxide, and it has a reference cell and a sample cell. To use this sensor properly, water vapor must be removed from the sample gas.?

Minimize Uncertainty

To minimize uncertainty, the experimenter should select measuring systems such that important readings will fall in the middle to upper portions of the range

Noise

Undesirable electrical interference causing degradation of a signal from sources such as electric machinery, ac power lines, and radio-frequency transmitters.

Crosstalk

Undesirable phenomenon in which the signal on one path interferes with other signals on other paths.

Fast Fourier Transform (FFT)

Used for spectral analysis: available on spreadsheet programs to help filter out noise or something? The function does not have to be periodic. FFT can perform DFT, and the higher the FFT sampling rate, the lower the amplitude of adjacent frequencies

Shielded and braided wire and single grounding method:

Used to minimize the signal transmission errors for low-level analog voltage signals (X)

time constant (tau)

Usually used for first-order dynamic systems. It is a characteristic time of a system indicating how fast the system will reach a steady state when subjected to a step change in input. It is defined as the time that the output change reaches 63.2 % of its final value

Bourdon gauge

Very common pressure measurement device, which works on the basis of deformation of a curved and flattened tube when the pressure inside the tube changes.

Precision

a measure of how close a series of measurements are to one another

Signal conditioning errors

caused by altering amplitude and phase of the signal

Info to purchase a filter

class corner frequency order type

Type K thermocouple

is the most common general-purpose thermocouple, corrosion resistant, and relatively linear thermocouple

capacitive displacement sensors

most appropriate for measuring very small displacements due to small pressures (~0.1 Pa)

Bit

smallest unit of binary information. A bit will have a value of 1 or 0. Bit stands for binary digit. eight bits make up a byte

Total uncertainty

the square root of the sum of the squared systematic uncertainty and random uncertainty