Khusainov F.F., Khakimyanov M.I.

Ufa State Petroleum Technological University

Designing of wireless sensors

Technological processes in fuel and energy complex of industry, such as production, transportation and refining of oil and gas, require deep introduction of automatic control systems. These modern control systems are multi-level complexes that provide maximum performance and reliability of process plants during the entire cycle.

The equipment of automatic control systems include sensors, different controllers, control stations and channels of data transmission, which can be, wired, optical, radio modem, cellular and satellite.

More recently, at designing such systems, there has been a trend towards the use of wireless technology as the use of sensors with wire interface often causes certain difficulties associated with mounting the sensors on moving and rotating objects, where the cable quickly wears out and breaks, as well as the installation of a remote and distant places. Also it should be noted that the organization of wireless communication channels, in most cases is much cheaper than laying the special cable networks [1, 2].

However, the use of wireless sensors associated with some operational disadvantages, such as the need for regular replacement of batteries, the range of radio transmission and of limited use because of the climatic conditions.

Decision of the above disadvantages could be the use new types of chemical batteries (lithium, silver-zinc and others) that have a high capacity (up to 10 A • h or higher), and keep working in a wide range of temperatures (at temperatures down to -30 ... 40 º C and below), as well as the emergence of new low-power electronic parts and radio interfaces for the design of sensors for long life operation without battery replacement [3].

One of the most promising ways to solve the problems described above is the use of alternative sources of energy: solar, heat, voltage generated by piezoelectric generator in the sensors of weight and strength.

Figure 1 shows a block diagram of a load cell with a wireless interface, which is powered by the electricity generated by the piezoelectric generator. The device is used for the registration dynacards of sucker rod pumps, driven by a pumping unit.

The load cell is installed in the node rope suspension of pumping unit and measures the effort generated between traverses with the reciprocating motion of the rod. The load cell comprises a sensing elements SE, measuring circuit IC, analog-to-digital converter ADC, a microcontroller and a radio transmitter IC RP. Power to all elements of the sensor from a battery that is recharged with electricity generated by the piezoelectric generator GHG its continuous cyclic loading.

1 – piezoelectric generator; 2 – battery; 3 – sensing elements; 4 – measuring circuit;  5 – analog-to-digital converter; 6 – microcontroller; 7 – radio transmitter

Figure 1 – Block diagram of a wireless load cell with piezoelectric generator

All electronic components of the sensor should have low power consumption, and in between measurements switch into a "sleep mode." Modern microcontrollers have quite energy efficient. In the "sleep mode" is provided to the consumption of 100 nA, the internal clock consumes 800 nA. Details of some of these MCUs are presented in Table 1 [4].

Table 1 - Comparison of microcontrollers

 

MSP430F21X1

PIC16LF72X

PIC18F14K50

PIC24F16KA102

Pin Count

20/24

28/44

20

20/28

Flash-memory of programs

4-8

3.5-14

8-16

8-16

EEPROM Data Memory

-

-

256

512

RAM, byte

256

368

768

1536

Consumption in the "sleep", nA

100

20

24

25

Time out from the "sleep", mks

3

5

5

1

Consumption of WDT, nA

700

500

450

420

Consumption of RTC, nA

700

500

790

520

Consumption when operating at a frequency of 1 MHz, uA

250

110

170

195

 

It should be noted that while reducing the level energy consumption of sensor developers limited speed and metrological characteristics of the device. Since the use of various software algorithms of digital signal processing, filtering and integration can significantly increase the current consumption of the microcontroller.

Thus, there may be made ​​the following conclusions:

1 The advantage of wireless sensors is the ability to install in remote and distant places, moving and rotating objects, where the use of devices with a wired interface is difficult.

2 Modern microelectronic element base allows the design of low-power devices that can provide continuous operation with battery.

3 When using alternative renewable sources of energy can significantly increase the continuous operation of wireless sensors.

 

 

 

 

 

 

 

 

 

References:

 

1. NI Wireless Sensor Networks: [site]. URL: http://sine.ni.com/np/app/main/p/ap/imc/lang/ru/pg/1/sn/n17:imc,n21:11297/.

2. Introduction to Wireless Sensors: [site]. URL: http://www.omega.com/prodinfo/wirelesssensors.html.

3.  M.I. Khakimyanov. Wireless technologies in industrial sensors // Improving the reliability and energy efficiency of electrical systems and complexes: Interuniversity collection of scientific papers / Editorial Board.: V.A. Shabanov. Ufa: USPTU, 2010. 189-198 p.

4. Compare 8-bit PIC® MCU Architectures: [site]. URL: http://www.microchip.com/pagehandler/en-us/family/8bit/architecture/home.html.