Practical Approach of using Embedded Controllers 2008/PDFs/20 Mircea RISTEIU.pdf · Practical Approach of using Embedded Controllers as Expansion System for Virtual Instrument over

CONFERINŢA NAŢIONALĂ DE INSTRUMENTAŢIE VIRTUALĂ, EDIŢIA A V-A, BUCURE�TI, 20 MAI 2008

Practical Approach of using Embedded Controllers as Expansion System for Virtual

Instrument over TCP/IP and 802.11 b/g protocols

Mircea RISTEIU, Bogdan CROITOR, Loredana BOCA

Abstract - We are developing a real time remote measuring system based on cRIO 9004 reconfigurable controller system for wind energy measurement. We use two modules, in chassis. We measure many heterogeneous types of parameters. The purpose of our approach is to exploit the performances of high speed FPGA and/or real time implementation via TCP/IP and 802.11g. Based on these aspects we have developed LabVIEW- based virtual instruments and we have tried to optimize measurements performances taking into account the sampling time, measurements delay, time delay processing, and desktop applications behavior. Running these VI for one criterion the main related expectations have been fulfilled. For combined criteria, some improvements have to be developed into the software side. Because of the desktop configuration, into remote measuring implementation some actual facilities of LabVIEW programming philosophy must be canceled. Index Terms - remote measurements, reconfigurable controller, virtual instrumentation, measurement delay, time delay processing, desktop configuration, wind energy.

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1. Introduction

We have started using LabVIEW implementation

for wind energy evaluation taking into account the

power of G-based programming.

The main requirement for using real time

measurement around LabVIEW implementation was

the demand for adding some environment

monitoring parameters to the main wind energy

parameters list. This aspect requested to mix together

some heterogeneous parameters. For that matter we

expect some parameters measurements to interfere

each other.

In our approach we use some sensors as follow:

• We have realised measurements of

enviromental parameters: temperature, wind

speed;

• Wind direction, noise level, stroboscopic

effect and 2 axes vibrations;

• Wind direction sensor (Wilmers);

• Wind speed sensor – anemomether (Thies);

• Atmospheric pressure sensor;

• Humidity sensor;

• Temperature sensor attached on the metallic

wind direction support;

• Crossbow Tilt Sensor (this sensor includes

vibration and temperature measurement

parameters);

Although we are measuring the level of solar

radiation and the electric energy generated by the

solar panel used for powering on the entire system.

Fig. 1 Deployed system

In Fig. 1 on a big steel pilon are attached two

solar panels, one temperature sensor and the data

acquisition device used for collecting data from

sensors. The data is sent to a computer through a

wireless connection.

The main advantage of this implementation is

based on the fact that the TCP/IP- based

reconfigurable controller allows us to organize a


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mobile measuring system with remote control

facilities.

For such issue, we have access to buss controller

and monitor, and remote terminal.

2. Using cRIO 9004

Fig. 2 cRIO 9004 device (controller)

A brief description of the reconfigurable controller

we use here will be figured next.

• cRIO-xxxx is a very performant data

acquisition device of NI;

• Extended work capacity;

• 512 MB of Nonvolatile memory enough for

any application running on cRIO controller

and for storing all the external recorded

parameters for many months;

• Power consumption: 7 W max only the

controller and 17 W max with 8 cRIO

modules;

• Real-time data transmition;

• Local and remote working capability;

• Both analog and digital input signals for

attached modules on cRIO chassis;

• Possibility of sending recorded data over a

large distance (remotely) through a secured

wireless connection (802.11 b/g);

• Configurated and programmed using the

FPGA and Real-Time Modules of Lab View

8.5;

• The Ethernet interface of cRIO directly

connected to a Wireless Access Point (D-link)

for sending data remotely;

• NI 9221 for data acquisition (analog I/O +/-

60V) plugged into cRIO chassis and in it’s 8

channels can be connected external signals;

• cRIO was programmed with NI-RIO 2.3

software package with all required

subcomponents (Visa server, Lab View 8.5,

etc…).

3. Network Configuration

With all fizical connections made, with all

equipements powered on and properly functioning,

we focused on other important aspect of the project –

Network Configuraton.

To transmit all recorded environmental data

from cRIO to a PC over a large distance (remotely)

we implemented a wireless network for this purpose.

cRIO was directly connected to a Wireless Acces

Point using an UTP cable, because both WAP and

cRIO were deployed close to each other and because

cRIO has only a TCP/IP Ethernet port for a network

cable connection.

The computer has been also connected to a

second WAP + a second antenna with the same

caracteristics as the first WAP.

For better wireless range we attached a very

powerfull antenna (25db power) to WAP, so in this

way data can be transmited over a bigger distance.

Fig. 3 cRIO – fizical connections

Figure 3 shows how external sensors have been

connected to cRIO. Every wire wich is plugged into

NI 9221 module represents an external sensor, so

each wire is transporting a signal from external

sensor to NI 9221 and each sensor is recording

different environmental parameters (different analog

signals).

Fig. 4 cRIO configured with MAX

(Measurement and Automation Explorer)


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We used MAX (fig. 4) to configure the Ethernet

interface of cRIO, to assign an IP and a name to the

device to be able to work in the network.

Both WAPs, cRIO and PC have IPs in the same

class and subnet. We gave a name to the network and

the wireless connection is protected using WPA 2

encrytion solution for high level of security . After

this step done we tested the conectivity and the link

between all devices in the network (PING command)

to see if the network is functioning or not.

Another aspect of the project was testing the

transmiting distance from the remote sensor to PC.

4. LabView Application

The most interesting and challenging part of the

project was the creation of a small application in

LabView 8.5 to effectively display and manipulate

the read data from all connected sensors.

And to do this we needed to create a new Lab

View project on a target device (in our case cRIO

named as “myRioK”).

We created two VIs: one on FPGA Target and

second on the REAL-TIME part (see Fig. 5).

Fig. 5 Project Explorer

The first VI called “FPGA buf read 2.vi” on

FPGA Target is reading the data from the channels of

NI9221 and store it into a FIFO for each channel

(buffer).

We used a FPGA I/O node to be able to read data

(signals) from NI9221 – cRIO. Four channels have

been read, each channel for different sensor (see Fig.

6).


4

Fig. 6 “FPGA buf read 2.vi” Block Diagram on

FPGA Target

Each “FIFO – read” has a numeric indicator

where data is displayed and these indicators are

invoked in the second VI to manipulate the contained

data (in real-time mode).

The second VI, named “Real time read-scalare

2.vi” (see Fig. 5), is realised on the REAL-TIME part

of the project and invokes the first VI and to be more

precise the four indicators (Element 4, Element 5,

Element 6, Element 7) are used and invoked as a VI

reference object on FPGA Target.

In this VI we made a few mathematic

calculations that are called calibrations wich means

we used a few linear transformations to adjust the

displayed value to the real value.

Generally these kind of sensors that we have

used are not factory default scaled, so the values

recorded and transmited needs a linear

transformation to display the real value.

For example we used a Crossbow Tilt Sensor

CXTLA 02 to measure the temperature and the

rotations on two ortogonal axes.

Without scalling the results, the sensor measured

a temperature value of 67 (not Fahrenheit - numeric

value), but outside were 18 degrees Celsius, so we

had to adjust the read value (67) to 18 (the real value)

using a simple linear transformation.

Fig. 7 “Real time read-scalare 2.vi” Block Diagram

on Real-Time part

The formula was found only with many tryes

and the accuracy of this formula is 95%. The general

formula used by NI to scale the results is:

(data_read_from_a_channel *

(the_addition_without_sign_of_the_inferior_and_s

uperior_limit_of_module_voltage / 2^

bit_resolution_module)). But this formula we had to

change it a little bit.

Depending on different sensors and different

signals, each channel might be scaled with different

formulas (see Fig. 7).

After that the results were displayed on the Front

Panel of the application in a few ways.

It was attached to this VI (inside it) a loop timer

to read data from cRIO only in specified time

intervals (dinamic control), because the speed of the

FPGA is 40Mhz (250 ns) and is a very big speed. You

cannot see the displayed data (numeric value)

because is changing very quickly.

A very important aspect is the oscillation of the

displayed value. That value is permanently changing

in a small interval. For example if the real recorded

temperature value is 18 degrees Celsius then the

application will display a value between 17,75 and

18,25.

5. Conclusions

Data acquisition system cRIO-9004 proves it’s

efficiency in acquiring a large variety of signals from

all external sensors directly connected to it’s modules

channels (in our case NI 9221).


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Although cRIO-9004 extends the boundaries of

sensoristic measurements and the remote

transmission aspect.

Using cRIO-9004 remotely with a lot of different

sensors deployed close to it and with a powerful

wireless connection you can very easy monitor a

large variety of environmental parameters in a

custom area. In this way you are able to make

predictions on collected / recorded data.

cRIO-9004 has 8 slots for attaching 8 different

data acquisition modules and, basically, you can use

almost any type of external sensor with cRIO without

problems.

In the future cRIO will be used in a pilot project

with a lot of environmental parameters sensors to

monitor a large area and after a year, based on

collected and analyzed data to choose building

between a farm of solar panels or a farm of wind

generators, as a free electric, nonpolluting,

regenerating energy source.

Fig. 8 Wind direction sensor with an attached

temperature sensor

All sensors in figures 8, 9, 10 have been used

with cRIO-9004. Parameters measured wind

direction, wind speed, temperature, light intensity

and rotations on 2 axes (vibrations).

Fig. 9 Solar Panel

Fig. 10 cRIO-9004 & Crossbow Tilt Sensor CXTLA

02 (rotations in two AXES and temperature)

BIBLIOGRAPHY

[1] *** LabVIEW 8.5 Development Guidelines; April 2007

Edition; National Instruments Corp. Austin, Texas,

U.S.A.

[2] *** LabVIEW 8.5 User Manual; April 2007 Edition;

National Instruments Corp. Austin, Texas, U.S.A.

[3] *** www.ni.com/support ;

[4] *** www.xbow.com ;

[5] *** T. Savu, G. Savu, “Informatică – Tehnologii

Asistate de Calculator”, Editura ALL, Bucureşti, 2000

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Practical Approach of using Embedded Controllers 2008/PDFs/20 Mircea RISTEIU.pdf · Practical Approach of using Embedded Controllers as Expansion System for Virtual Instrument over