More books in category: Signal Conditioning
by: IOTech
AMAZON multi-meters discounts AMAZON oscilloscope discounts
Topics include:
CLICK HERE for more information and price
The Signal Conditioning Handbook is intended for newcomers to the field of data acquistion and signal conditioning. Emphasis is given to general discussions of ADC measurement and the signal conditioning requirements of selected transducer types.
The latest revision has been in development for nearly a year, expanding coverage to include new sensor types that have emerged since the last publication, as well as expanded coverage of additional topics including:
* Analog to Digital Conversion
* Multiplexing
* Electrical Measurements
* Fundamental Signal Conditioning
* Temperature Measurement
* Strain Measurements
* Vibration and Sound
* Displacement and Position Sensing
* Noise Reduction and Isolation
* Digital and Pulse Train Signal Conditioning
* Transducer Electronic Data Sheets
PREFACE to the Third Edition The third edition of this handbook has been totally revised to include new chapters on Electrical Measurements, Vibration and Sound, Displacement and Position Sensing, and Transducer Electronic Data Sheets (TEDS). It also includes several new subjects and expands on selected items including Fundamental Signal Conditioning. All chapters have been enhanced to address more practical applications than theoretical measurement issues. They cover a major topic with sufficient detail to help readers understand the basic principles of sensor operation and the need for careful system interconnections. The handbook also discusses key issues concerning the data acquisition system's multiplexing and signal conditioning circuits, and analog-to-digital converters. These three functions establish the overall accuracy, resolution, speed, and sensitivity of data acquisition systems and determine how well the systems perform. Data acquisition systems measure, store, display, and analyze information collected from a variety of devices. Most measurements require a transducer or a sensor, a device that converts a measurable physical quantity into an electrical signal. Examples include temperature, strain, acceleration, pressure, vibration, and sound. Yet others are humidity, flow, level, velocity, charge, pH, and chemical composition. Sensors come in numerous shapes, sizes, and specifications. They connect between the measured physical device and the signal conditioner's input. Most sensors are purchased off-the-shelf, but in some cases, they are custom made specifically for a particular measurement requirement. Regardless of input, however, the output signal is usually a voltage, current, charge, or resistance and all can be conditioned and handled equally well. Manufacturers frequently provide specifications, application notes, and principles of operation for their specific sensor to help users apply the device in the most efficient way. Signal conditioners accept sensor output signals and convert them into a form that the data acquisition system can manipulate. Signal conditioners typically amplify, filter, isolate, and linearize these signals. They also convert current to voltage and voltage to frequency, provide other functions such as simultaneous sample and hold (SS&H), and supply a bias voltage or signal excitation for certain transducers. They may come with single-ended inputs or differential inputs for improving signal-to-noise ratios. The output of the signal conditioner, in turn, connects to the input of an analog-to-digital converter (ADC) embedded within the data acquisition system. Finally, the ADC converts the conditioned analog signal to a digital signal that can be transferred out of the data acquisition system to a computer for processing, graphing, and storing. Introduction to Data Acquisition and Signal Conditioning Chapter 1 discusses signals, sensors, and signal-conditioning techniques and how they relate to data acquisition system fundamentals. It also covers personal computers and how laptop or notebook computers work with data acquisition systems. Analog-to-Digital Conversion Chapter 2 discusses four basic ADC types, including their accuracy and resolution. Also covered are topics such as ADC output averaging, discrete sampling, input and source impedance, and differential voltage measurements. Yet others include simultaneous sample and hold methods, selectable input ranges, aliasing, digital filtering, and Fourier Transforms. Multiplexing Chapter 3 covers the fundamental principles of multiplexing and their benefits and economies. Electrical Measurements Chapter 4, Chapter 6, Chapter 7, Chapter 8, and Chapter 9 discuss basic electrical measurements, the characteristics of various sensors, how to use sensors to measure the most common types of electrical and physical quantities, and the signals that they represent. Topics include voltage, current, resistance, charge, temperature, strain, position, velocity, acceleration, and sound. The sensors that produce them include thermocouples, RTDs, thermistors, strain gages, accelerometers, and linear and rotational displacement sensors. Fundamental Signal Conditioning Chapters 5 and Chapter 11 discuss the most widely used techniques for analog, digital, and pulse-train signal conditioning. They comprise operational, differential, and high-gain amplifiers for filtering, attenuation, isolation, linearization, and circuit protection for analog signals. They also cover topics on digital I/O interfacing, frequency measurements, and pattern generation for digital signals. Noise Reduction and Isolation Chapter 10 is dedicated to simplifying the somewhat difficult topic of electrical noise interference, using the best shielding and grounding techniques, and identifying the major sources of crosstalk. It also discusses how to select the proper amplifiers and sensors, as well as how to use certain isolation and wiring techniques to minimize or eliminate significant noise in data-acquisition systems. Transducer Electronic Data Sheets (TEDS) Chapter 12 covers Transducer Electronic Data Sheets. TEDS is a class of so-called smart sensors that contain an onboard memory chip. The chip stores information regarding transducer calibration, manufacturer information, and many other data.
Chapter 1
Introduction to Data Acquisition and Signal Conditioning
SIGNALS, SENSORS, AND SIGNAL CONDITIONING
All industrial processing systems, factories, machinery, test facilities, and vehicles consist of hardware components and computer software whose behavior follow the laws of physics as we understand them. These systems contain thousands of mechanical and electrical phenomena that are continuously changing; they are not steady state. The measurable quantities that represent the characteristics of all systems are called variables. The proper functioning of a particular system depends on certain events in time and the parameters of these variables. Often, we are interested in the location, magnitude, and speed of the variables, and we use instruments to measure them. We assign the variables units of measure such as volts, pounds, and miles per hour, to name a few.
Most variables must be measured with a device that converts the phenomena into a form that a human can perceive such as a visual display, a transducer for sound, or vibrations to stimulate physical sensations. The conversion devices are called transducers or sensors, and they translate the physical phenomena to electrical signals (or vice versa) to be measured with electronic instruments. These instruments have traditionally been ammeters, voltmeters, and various other gages, and the variables can be observed in real time. But an increasing need to record and preserve these phenomena and analyze them at a later time forced engineers to develop data recorders and data acquisition systems.
Variables may be classified in many ways, but generally, most experts prefer two classifications: by characteristic and by type of measurement signal. Variables classified by characteristic include thermal, radiation, force, rate, quantity, time, geometric, physical properties, chemical composition, and electrical. Those classified by measurement signal include motion, force, electrical, and time-modulated. Measurement signals for variables often are hard to differentiate from the measuring system. Four factors require close consideration for measurement signals and systems: the types of transducers available for converting variables to measurement signals, transmission characteristics, data acquisition system input matching, and transducers available to convert from one type of measurement signal to another measurement signal.
DATA ACQUISITION SYSTEMS
Data acquisition systems have evolved over time from electromechanical recorders containing typically from one to four channels to all-electronic systems capable of measuring hundreds of variables simultaneously. Early systems used paper charts and rolls or magnetic tape to permanently record the signals, but since the advent of computers, particularly personal computers, the amount of data and the speed with which they could be collected increased dramatically. However, many of the classical data-collection systems still exist and are used regularly.
PC–BASED DATA-ACQUISITION EQUIPMENT
Early, expensive mainframe computers were used extensively for gathering multiple channels of data, primarily in large industrial or scientific applications. They were seldom used in small projects because of their relatively high cost. But the introduction of small rack-mounted minicomputers that developed in the 1960’s and later desktop personal-type computers that housed microprocessors and proliferated in the 1970’s justified their use for smaller projects. Soon, data acquisition plug-in cards (as well as hundreds of other types of plug-in cards) for these small computers were a common means to collect and record data of all types.
Plug-in cards for computers did not always perform to the user’s expectations, however. Internal noise from rotating devices such as drives and electromagnetic and electrostatic noise from the computer’s internal bus structure often interfered with the measured variable, particularly in data acquisition cards. Isolation and shielding have helped to solve the problem in most cases, but many data acquisition manufacturers also provide signal conditioning and signal processing circuits in small, stand-alone, shielded enclosures. The separate box provides isolation by distance, expansion for hundreds of channels, and portability with laptop computers that desktop personal computers with plug-in cards don’t possess.
All PC-based data acquisition systems will record extremely accurate, repeatable, reliable, and error-free data provided they are connected and operated according to the manufacturer’s recommended practices. These practices include selecting the correct sensors for the application, the proper wire and shielded cable; capturing the signals in proper magnitude, range, and frequency; and paying close attention to grounding and shielding – particularly eliminating ground loops. Additional items include choosing the correct impedance and using doubled-ended (differential) inputs instead of single-ended where possible. The environment should also be considered, especially for extremes of ambient temperature, shock, and vibration. And herein lies the major goal of this publication – to inform users of the most needed recommended practices based upon a fundamental knowledge of the internal workings of data acquisition system instrumentation.
Reviews: