Data Logging and Analysis

8/3/2019 Data Logging and Analysis

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DATA LOGGING AND ANALYSIS BY VIRTUAL

INSTRUMENTATION

Nicolae PATRASCOIU Adrian Marius TOMUS

Department of Automation, Industrial Informatics and Computers

University of PetrosaniUniversităţii 20, Petroşani, România

[email protected]

Abstract: Real-world data logging applications are typically more involved than

just acquiring and recording signals, typically involving some combination of online

analysis, offline analysis, display, report generation, and data sharing. In this paper

we propose a virtual instrument (VI) that converts a PC into a data logger and also

the same instruments are used to offline analysis of measured and recording data and

to sharing data with another application like Excel. Measurement signals are

converted into measurement data aid A/D converter CA3162E follow-up recording

via LPT port.

Keywords: data logging, A/D converter, LPT, data analysis, LabView

1. Introduction

Basic elements of a data logging and analyzing system are presented in figure1.

Acquiring is the process of actually measuring the physical parameters and bringing theminto your logging system. Online analysis consists of any processing done to the data while

are acquiring. It includes alarms, data scaling, and sometimes control, among others.

Logging is an obvious requirement of

every data logging system. Offlineanalysis is everything done with the data

after it has been acquired in order to

extract useful information from it. Thefinal functional block is made up display,

reporting, and data sharing. These are all

the “miscellaneous” requirements that fillout the functionality of a data logging

system [5].

Online

Analysis

Data

Logging

Online

Analysis

Display,

Sharing,

Reporting

Acquire

Fig.1. Basic elements of a data logging and

analysis system

2. Analog-to-digital conversion

In this paper we consider a stand-alone analog–to–digital converter CA3162E product by Intersil Corporation. The CA3162E and CA3162AE are I2L monolithic dual

slope analog-to-digital converters that provide a 3 digit multiplexed BCD output. They areused with the BCD–to–Seven–Segment Decoders/Drivers and a minimum of external parts

to implement a complete 3–digit display used in many digital multimeters (DMM). Thisanalog–to–digital converter generate at output not a binary code and we consider the output

signal done by a 7 bits word respectively 4 bits for BCD code of digit (BCD OUTPUTS)

and 3 bits for digit selection (MSD, NSD and LSD). With these 7 bits code is necessary to

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display measured value and to store consecutive

values into properly file so that these codes areacquired through LPT port [1]. For this the ones

7 bits are connected to the data section (pins 2 to

9, D0 … D7) of the LPT port like diagram

presented in fig.2.

3. Virtual Instrument

Software is of critical importance in PC-

based data logging systems, because well-written logging software determines how data is

stored, how quickly data can be written to disk,

and how efficiently disk space is used and givesdifferent data management capabilities.

The software use, in this paper, to create

a PC-based data logger is LabVIEW and alsothe same LabVIEW programs, that are called

virtual instruments or VIs, are used for offline

analysis. Every VI uses functions that

manipulate input from the user interface or other sources and display that information andevery VI has two components front panel respectively diagram bloc.

3 x 100 kO

4 x 100 kO

NSD

MSD

LSD

23

22

21

20

3

5

16

15

1

7

4

V+IN

V-IN

10 kO

50 kO

2

13

10

11

4

8

9

1214

0,27 µF

INPUTSIGNAL

Hold

+ 5V

+ 5V

D0

D1

D2

D3

D4

D5

D6

CA3162

Fig. 2. LPT converter connection

The VI that perform both basics function that are data logging and data analysis has

two mains front panels ONLINE ACQUISITION respectively OFFLINE ANALYSISselected by means of the Tab Control.

3.1. Acquisition Virtual Instrument

The front panel corresponding to ONLINE ACQUISITION is presented in fig.3.

and this front panel is used to control acquisition process and also to display the important

parameters of the acquisition process like acquisition state or measured values and alsorecord date and time. There are three components that are waveform graph in stack plot and

two blocks Acquisition

Control that controlacquisition parameters

like parallel port address

number of acquisitions,number of points per

acquisition respectively

Acquisition Progress that

show in different formcurrent value acquired.

Waveform graph display

the filtered and nonfiltered form of the

acquired signal.Fig.3. ONLINE ACQUISITION Front Panel



To ensure the read bits on data section on the LPT port is used a Sequence

Structure where the first 3 sequences are used for LPT settings [3]. All other programelements are included into a While Loop that repeats the subdiagram inside it until the

conditional terminal, an input terminal, receives a particular Boolean value so that

acquisition can be interrupt by user. After port settings is select the file where are storage

the measured values and for that are used File Dialog respectively New File. The programcan assure one ore more acquisition; number of these is selected by properly control and

number of points of every this acquisition that mean number of values is also selected by

properly control, both on the front panel.

Fig.4. ONLINE ACQUISITION Diagram Bloc

One of the most important sections of the diagram bloc is conversion section

(fig.4.). In this section the 7 bits word acquired is converted into same numerical

representation. To obtain the last one numerical respectively value acquired is used 3 Case

Structure. One of these is selected by properly bit corresponding MSD, NSD and LSD

analog–to–digital converter outputs connected at D4, D5 and D6 bits of the LPT port and

wired to the selected terminal. All that structures are included into a For Loop where

controls value Points/Acquisition is the value wired to the count (N) terminal.Every structure contains a subdiagram (SubVI) BCD-NUM.vi [2] that computes the

right value of the 4 last significant bits. These bits represent the corresponding BCD code

for tenths, units respectively tens. The conversion in whichever structure, only when this

are selected, in decimal number Nr is accomplished by relation:3

32

21

10

0 2D2D2D2D Nr ⋅+⋅+⋅+⋅= (1)

were Di represent bits of the BCD output of the analog–to–digital converter and the value V acquired has the form:

Nr 10D Nr D Nr 10DV 651

4 ⋅⋅+⋅+⋅⋅=−

(2)



Every values generates by For Loop are displayed under numerical value form and

are logging and displayed also under graph form by the Acquisition Results window. At thesame time are generating by Get Date/Time String the real time called record which will

be associated to the stored data. Logging data are definite by using Circuit Interface Nod

(CIN) Write File that writes data to an open file specified by refnum and after

performance [6].For cut the spikes inlays by analog–to–digital converter is used Median Filter that

applies a median filter of rank to the input data sequence. The result of this operation is to

filter the signal represented by input data sequence and on the Front panel it can observe thedifference.

3.2. Analysis Virtual Instrument

The terms "data analysis" and "statistics" mean the same thing, the study of how we

describe, combine, and make inferences from numbers. A lot of measured are scared of numbers, but statistics has got less to do with numbers, and more to do with rules for

arranging them. There are three general areas that make up the field of statistics and one of

these is descriptive statistics which fall into one of two categories: measures of centraltendency (mean, median, and mode) or measures of dispersion (standard deviation and

variance).

LabVIEW offers many of built-in analysis functions that cover different areas and

methods of extractinginformation from

acquired data. With these

functions it can be makea virtual instrument (VI)

that front panel has two

components switching bya proper Tab Control

between SAMPLE

RECORD and DATA

RECORD that meananalysis of every 2000

acquiring points (one

sample) or all datarepresenting acquiring

points. The VI

corresponding to onesample and to all data is

presented in fig.5.

Passed

Data

Lower Failed Data

Upper Failed Data

On that panel arearranged the indicators

elements that assure the

visualization the results

of the data analysis aboutmeasured and recorded

values. Those elements

indicate, at one time withFig.5. OFFLINE ANALYSIS Front Panel



record time the limits values and statistical values. For the limit values are indicate also the

time when these limits are accomplished. The statistical values represent the statistic parameters described above that is mean, standard deviation and variance computed

Two Waveform Graphs are used to the graphical analysis. One of these display the

graphical evolution of record data i.e. the measured signal and for this exist possibly to

setup the lower and upper limits. Another display time period for that data is in excess of lower or upper limits. The base element of the diagram bloc (fig.6.) is While Loop that

repeats the subdiagram inside while is processing all recorded data. At this loop, are

attached elements by that are opened and closed corresponding file. The limits values aredetermined by Statistics.vi which determines maximum and minimum values and their

associated time value for the recorded data waveform.

The current statistic values are determined by the same Statistics.vi which

computes the mean, standard deviation, and variance of the values in the input sequence X.

For this bloc, the weighting input, which determines whether to calculate the population or the sample standard deviation and variance, is setting to the default value i.e. the statistic

values are compute for a sample of measured values. The Mask and Limit Testing.vi

perform limit testing on the input waveform i.e. recorded data. It compares the input signalwith the upper and lower limits and

ignores the limit that is not wired. It

returns a TRUE if the signal is less

then or equal to the upper limit andgreater than or equal to the lower limit.

It returns a FALSE instead. The

outputs witch contains the results of the comparison at each data point and

an array of waveforms containing the

upper limit and lower limit, the signal,and the failures.

Fig.6. OFFLINE ANALYSIS Diagram Bloc

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150Time

M e a s u r e d V a

l u e

Fig.7. Excel Data Representation



Use LabVIEW measurement data files To save measurement data files is use the

Write LabVIEW Measurement File Express.vi generates. The LabVIEW data file is atab-delimited text file that can open with a spreadsheet application like Microsoft Excel or a

text-editing application. The recorded data with graph representation in Excel for the same

acquisitions data sequences are presented in figure 7. In addition to the data an Express.vi

generates, the .lvm file includes information about the data, such as the date and time thedata was generated.

5. Conclusions

Using data logging offer the possibility to follow up the evolution for a system or process variable for a long time.

PC-based data logging systems provide the most flexibility, customization, and

integration. The PC-based data logging systems propose in this paper can be simple makingusing a usual DMM from which is enough to ladle out the signals generate to display. This

signal can be different from DMM to DMM but is so easy to adapt the VI to proper signals

form. We are consider a difficult case where analog–to–digital converter provide a 3 digitmultiplexed BCD output but if digits are not multiplexed the solution for VI are simplest.

We are consider also that LabVIEW which is a soft dedicated to data acquisition

satisfy the requests for data logging software. Aid a virtual instrument can create

applications that provide dialogs and interfaces that can use so that depending on their input, specific analysis routines are performed on any given data set. By building this type

of application, users build a certain degree of interactivity into their applications.

References

[1].CIASCAI, I. 1998. Sisteme de achizitie de date pentru calculatoare personale.

Ed. Albastra, Cluj-Napoca, 1998; pp 125

[2].PATRASCOIU, N. 2004Sisteme de achizitie si prelucrare a datelor. Instrumentatie

virtuala. Ed. Didactica si Pedagogica, Bucuresti, 2004; pp

258[3] PATRASCOIU, N. 2002. Modelarea şi simularea prin utilizarea instrumentaţiei

virtuale. In Revista de Instrumentatie Virtuala.Cluj-Napoca,

Romania, 2002; pp 5-8,ISSN 1453-8059[4]. * * * .2001. A Review of PC-Based Data Logging and Recording

Techniques. National Instruments, December.2001

[5] * * *. 2003. LabVIEW for Measurement and Data Analysis

National Instruments, January.2003

[6]. * * *.2003. LabVIEW. User Manual. National Instruments, April 2003

Edition Part Number 320999E-01

Data Logging and Analysis

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