Patrick Goell: How to turn a personal computer into a measuring system. Göll P

The modern computer is the most complex electronic device. Combining the technical complexity of individual components and the design simplicity of their combination and expansion, the user, more than ever before, has the freedom to connect various peripherals to it, expanding its capabilities infinitely. One of these possibilities is the use of a computer as a measuring system. Indeed, it is enough to transfer some signal or measured value into it, and the possibilities for their digital processing, as well as display in an arbitrary, user-friendly form. Patrick Goell's book "How to turn Personal Computer» into the measuring complex.

The book begins with a brief introduction that introduces the reader to the basics of designing measurement systems. The author draws attention to the main stages of measurements and shares the basics of analog-to-digital signal processing. The topic of ADC is covered in detail in the corresponding chapter. What an ADC is, how an ADC works, what the principle of converting an analog value into digital form is based on, and how this can be done is described in this book.

The task of measuring various quantities is very common in production. What standards and standard solutions exist to solve this problem in professional production are described in the third chapter of the book. The author dwells on industrial developments devoted to this topic. Reveals the typical characteristics of such devices.

In the fourth chapter of the book we're talking about O homemade devices for digitizing analog quantities. Schemes and printed circuit boards similar devices. The principles of operation are described so that in the future the reader can create a similar device of his own design.

Naturally, a computer measuring complex cannot operate without a special software. The latter must be able to read the signal, evaluate its absolute value, and present the resulting value on the computer screen in a convenient form. How such applications are developed is described in the fifth chapter of the book.

A major role in the reliability of measurements is played by sensors, or primary transducers, which are connected to a computer. An overview of such sensors is given in the sixth chapter.

Introduction
1. Concept of constructing a virtual measuring complex
2. Analog-to-digital signal conversion
3. Industrial products
4. Assembling the measuring interface
5. Software of the virtual measuring complex
6. Sensors and accessories
7. Applications

Göll Patrick

“How to turn a personal computer into a measuring complex”

Your PC: tester, oscilloscope, data logger...

Introduction

Any IBM-compatible personal computer (PC), even if it has been lying in the back of a closet for several years as unnecessary, can turn into a powerful measuring system if it is equipped with one or more analog inputs. Its keyboard and screen provide significantly greater capabilities compared to those that can be provided by a multimeter or oscilloscope, and its disk drive and printer are excellent for recording any lengthy processes. In addition, the computing power of a PC allows the information data collected with its help to be subjected to any, even very complex, processing. Just a few years ago, turning a PC into a virtual measuring instrument required installing one or more complex and expensive boards into the computer.

This approach is still used in industry and scientific laboratories, but today it is also possible to achieve decent results simply by connecting small analog-to-digital converters to standard serial or parallel ports. There are ready-made products on the market offered at an affordable price, but such devices can be assembled independently, guided by the diagrams and recommendations given in this book.

Thanks to the library of drivers that are intended for the devices described, this book and the files located on the www.dmk.ru server will allow the reader to quickly move on to practical work, whatever his level of knowledge in the field of electronics.

All of the problems covered here are provided with ready-to-use programs, and can be adapted to suit other needs with just a few changes in BASIC. Thus, which is very important, the virtual measuring complex is reprogrammable.

Today it is customary to call all at least somewhat non-standard applications for personal computers “virtual”. Many useful things can be simply simulated on a good color screen with high resolution, and the result will often look “better than it really is.”

So, on the virtual screen measuring instrument a complex, rich picture will probably be presented, on which there are buttons, and various indicators, and scales, and even oscilloscope screens. Graphical interface capabilities Windows type provide a much wider range of applications than a conventional measuring instrument can have - not to mention the potential use of printers, disk drives, and an Internet-connected modem.

The virtual device itself is a more or less complex software installed on a personal computer, and a certain interface device that allows the PC to gain access to the physical quantities and processes that it will have to process. As a rule, such an interface is an analog-to-digital converter with one or more inputs, possibly equipped with an input signal conditioning device.

In principle, you can count on the fact that the virtual device will provide its owner with much more ample opportunities, and the price will be comparable to a classic measuring device with the same level of technical characteristics.

This approach allows us to limit ourselves to minimal costs if the requirements for the measuring complex are not very stringent. Such a solution is ideally suited to the needs of radio amateurs, teachers and even some research laboratories that deal with relatively slow physical processes. In addition, this makes it possible to return to active and useful work the oldest of the IBM-compatible PCs, which, it would seem, are doomed to quietly gather dust in the depths of cabinets and closets thanks to the mind-blowing evolution computer technology(and the policies of PC and software companies).

Göll Patrick

“How to turn a personal computer into a measuring complex”

Your PC: tester, oscilloscope, data logger...

Introduction

Any IBM-compatible personal computer (PC), even if it has been lying in the back of a closet for several years as unnecessary, can turn into a powerful measuring system if it is equipped with one or more analog inputs. Its keyboard and screen provide significantly greater capabilities compared to those that can be provided by a multimeter or oscilloscope, and its disk drive and printer are excellent for recording any lengthy processes. In addition, the computing power of a PC allows the information data collected with its help to be subjected to any, even very complex, processing. Just a few years ago, turning a PC into a virtual measuring instrument required installing one or more complex and expensive boards into the computer.

This approach is still used in industry and scientific laboratories, but today it is also possible to achieve decent results simply by connecting small analog-to-digital converters to standard serial or parallel ports. There are ready-made products on the market offered at an affordable price, but such devices can be assembled independently, guided by the diagrams and recommendations given in this book.

Thanks to the library of drivers that are intended for the devices described, this book and the files located on the www.dmk.ru server will allow the reader to quickly move on to practical work, whatever his level of knowledge in the field of electronics.

All of the problems covered here are provided with ready-to-use programs, and can be adapted to suit other needs with just a few changes in BASIC. Thus, which is very important, the virtual measuring complex is reprogrammable.

Today it is customary to call all at least somewhat non-standard applications for personal computers “virtual”. Many useful things can simply be simulated on a good, high-resolution color screen, and the result will often look "better than it really is."

So, the screen of the virtual measuring instrument will most likely present a complex, rich picture, on which there are buttons, various indicators, scales, and even oscilloscope screens. The capabilities of graphical interfaces such as Windows provide a much wider range of applications than a conventional measuring instrument can have - not to mention the potential use of printers, disk drives, and an Internet-connected modem.

The virtual device itself is a more or less complex software installed on a personal computer, and a certain interface device that allows the PC to gain access to the physical quantities and processes that it will have to process. As a rule, such an interface is an analog-to-digital converter with one or more inputs, possibly equipped with an input signal conditioning device.

In principle, you can count on the fact that a virtual instrument will provide its owner with much greater capabilities, and the price will be comparable to a classic measuring instrument with the same level of technical characteristics.

This approach allows us to limit ourselves to minimal costs if the requirements for the measuring complex are not very stringent. Such a solution is ideally suited to the needs of radio amateurs, teachers and even some research laboratories that deal with relatively slow physical processes. In addition, this makes it possible to return to active and useful work the oldest of the IBM-compatible PCs, which would seem doomed to quietly gather dust in the depths of cabinets and closets thanks to the mind-blowing evolution of computing technology (and the policies of PC manufacturing companies and software).

1. CONCEPT OF BUILDING A VIRTUAL MEASURING COMPLEX

Below is the concept of constructing a virtual measuring complex based on a personal computer and considers the tasks that can be solved using the components of this complex.

ROLE OF THE COMPUTER

A computer (most often IBM-compatible, desktop or portable) as the central organ of any virtual measuring system primarily performs the functions of the “person-measurement object” interface. The screen of any monitor provides much more possibilities for indication than the screen of an oscilloscope (even if it is a storage one), and, of course, the monitor screen is much larger than the display of a multimeter. The keyboard and especially the mouse are much more convenient to use than buttons, and a printer - even the simplest one - provides invaluable opportunities for printing results on paper. In addition, any PC, even a very “ancient” one, has a lot of computing power, which can be used to apply various types of processing of measurement results: normalization (scale reduction), linearization, timing, calculating the average, statistics, etc. d. Finally, a disk drive will be very convenient for accumulating large amounts of data for the purpose of subsequent processing, archiving, or transmission over communication lines using a modem.

ROLE OF INTERFACE DEVICES

Measuring physical parameters such as voltage, current, temperature or pressure involves accurately estimating analog quantities. The computer works exclusively with discrete quantities. It is clear from this that the process of turning a PC into a virtual measuring instrument involves connecting an analog-to-digital converter (ADC). The ADC can communicate with the computer either through serial or parallel ports, or directly through buses if the analog-to-digital converter is in the form of an expansion card or PCMCIA card.

The first option guarantees maximum simplicity and low cost, while using the second you can get excellent performance, but only at the expense of complexity and high price. The interface device can also perform other necessary functions, e.g. galvanic isolation sources of signals from PC circuits, matching of signals generated by certain types of sensors by impedance, voltage, polarity, etc., as well as switching of several input channels.

ROLE OF SOFTWARE

The scope of application of a virtual instrument is almost entirely determined by the characteristics of the software, while the characteristics of interface devices are in most cases quite clear to the user.

Industrial products of this kind are almost always used when working with a more or less developed graphical interface (by the way, not always under Windows), which allows you to select one or another mode using the keyboard or mouse through various menus (Fig. 1.1).

Figure 1.1. Example of Virtual Meter OSD Menus

As will be shown later, it is very convenient to create small programs specifically designed to perform a particular practical task. They are often written in such a popular and in simple language, like BASIC. A slight structuring of these programs will make it possible to use both industrial interface devices and devices independently assembled from individual elements by simply reinstalling the appropriate driver. Below we will compare both options, so that readers can choose the solution that best suits their personal needs, technical and financial capabilities, and, finally, programming talents.

In addition to running data acquisition programs, the virtual instrument user will be able to frequently export measurement results to more advanced applications such as spreadsheets or charting programs. These office applications make the most abstract records or data sets understandable, highlighting trends or relationships that are invisible at first glance. And, of course, digital data files obtained by recording measured physical parameters can be transmitted over communication lines using a modem, in particular via e-mail and via the Internet.

ACCURACY AND SPEED

When comparing between real and virtual devices, in addition to the provided capabilities and operating modes, one must also take into account their main characteristics, namely accuracy and speed.