Theory

What is Wi-Fi or WLAN?

Wi-Fi or Wireless Fidelity or Wireless Local Area network is a popular technology that allows an electronic device to exchange data wirelessly (using radio waves) over a computer network, including high-speed Internet connections. For example, 802.11 WLANs are able to transmit and receive at a variety of data rates and switch between them dynamically.

A system that can use Wi-Fi can connect to a network resource such as the Internet via a wireless network access point. Such an access point (or hotspot) has a range of about 20 meters (65 feet) indoors and a greater range outdoors.

Various Terms Used in Wi-Fi.

1. Frequency Band: Frequency bandwidth of carrier frequency used for data transfer.

2. Data rate: Measurement of volume of data getting transferred per second ( generally given in Mbps)

Data Rate = n* Acquisition rate (in sample/sec) * Resolution (in Bits/Sample)

Where n = Total number of data input channels.

4. Encoding: It is manipulation of radio waves in a predefined way.

5. Range: This is the maximum distance at which two radios can operate and maintain a connection.

6. Throughput: It is average rate of successful message delivery through a communication channel.

7. SNR: It is defined as the ratio of signal power to the noise power.

Advantages of using WiFi

  • There is a reduced labor and material cost required to hardwire the isolated assets.
  • Wireless input output generally require only end point to be installed and configured. It saves the times for projects with forceful schedule.
  • Capacity of wireless can be increased by simply installing additional components. In effect it's"pay as you go" architecture.
  • Wireless provides a facility of communication alarm as it let the user know that the data is no longer being received from instrument due to loss of signal between the server and the instrument.
  • Wireless has also got features like reliability, safety, flexibility and low power consumption.

Architecture of Wireless Condition Monitoring System

For a conventional on-site machine condition monitoring system, data flows from physical raw data to final machine-condition judgment. To extend an on-site monitoring system to a remote one, the data flow is the same as before, but the difference is that raw-data acquisition and machine-condition judgment are at two various sites so that Internet communication techniques are employed. The architecture of the developed remote diagnostic system composes of three key parts

(1)Acquisition hardware.

(2)Working environment and communication interface.

(3)Analysis-tool modules, which complete an effective monitoring system.

Two types of computer networks, i.e., peer/peer and server/client types are generally applied in communication tasks. Moreover, a server/client computer network can be realized in two different arrangements. That is, one is the server end at a control center and the client end beside the machines to be monitored, and the other is vice versa. Presently in this study we have used National Instrument® Wi-Fi data acquisition device (DAQ) WLS-9234 wireless 4-channel accelerometer and microphone input combined with NI® WLS-9163 and C-series hardware.

In case of wired and wireless machine condition monitoring, acquisition hardware and analysis tool module are almost same. However communication interface is main difference between two.In our study we have taken wireless LAN as communication interface.