Discussion

Exercise 7. Work in pairs or in small groups. Share in the discussion. Use the following questions as prompts:

1) Could you interpret the term “DSP” and give its definition?

2) What is the general purpose of DSP?

3) Would you describe the initial stage of digital signal processing?

4) What is an ASIC?

5) What additional technologies are used for digital signal processing nowadays?

6) What domains of studying digital signals in DSP do you know?

7) How can you correlate a discrete Fourier transform with DSP?

8) Could you name the most important – from your point of view – applications of DSP?

9) What items may be used for faster DSP applications? And for slower ones?

Lesson 4 what is a sensor?

Lexical units:

touch-sensitive – сенсорный

to dim – гаснуть

output – выходной сигнал

microscopic scale – микроскопический уровень

MEMS technology – технология микроэлектромеханических систем

to merge into – переходить, превращаться во что-либо

to implement – выполнять, осуществлять

target device – конечный прибор

to obey the rule – соответствовать правилу

linear – линейный (применительно к функции)

deviation – отклонение, девиация

sensitivity error – ошибка чувствительности

dynamic error – динамическая ошибка

bode plot – представление амплитудно-фазовой частоты в логарифме

phase shift – сдвиг по фазе

to some extent – до некоторой степени

random error – случайная (несистематическая) ошибка

resolution – разрешающая способность

to fluctuate – колебаться

scanning tunneling probe – сканирующий туннельный микроскоп

fine – тонкий

tip – наконечник

TEXT

Sensors are used in everyday objects such as touch-sensitive elevator buttons and lamps which dim or brighten by touching the base. There are also innumerable applications for sensors of which most people are never aware. Applications include cars, machines, aerospace, medicine, manufacturing and robotics.

A sensor is a device which receives and responds to a signal. A sensor’s sensitivity indicates how much the sensor’s output changes when the measured quantity changes, i.e. a sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For instance, if the mercury in a thermometer moves 1 cm when the temperature changes by 1 °C, the sensitivity is 1 cm/°C. Sensors that measure very small changes must have very high sensitivities. Sensors also have an impact on what they measure – a room temperature thermometer inserted into a hot cup of liquid cools the liquid while the liquid heats the thermometer. Sensors need to be designed to have a small effect on what is measured, making the sensor smaller often improves this and may introduce other advantages.

Technological progress allows more and more sensors to be manufactured on a microscopic scale as microsensors using MEMS technology. MEMS (micro-electro-mechanical systems) is the technology of very small mechanical devices driven by electricity. It merges at the nano-scale into nanotechnology. MEMS technology can be implemented using a number of different materials and manufacturing techniques, depending on target device and market sector. The most common materials here are silicon, polymers, and metals.

A good sensor usually obeys the following rules: 1) it is sensitive to the measured property; 2) it is insensitive to any other property likely to be encountered in its application; 3) it does not influence the measured property. Ideal sensors are designed to be linear to some simple mathematical function of the measurement, typically logarithmic. The output signal of such a sensor is linearly proportional to the value or simple function of the measured property. The sensitivity is then defined as the ratio between output signal and measured property.

If the sensor is not ideal, several types of deviations can be observed. For example, the sensitivity may in practice differ from the value specified. This is called a sensitivity error, but the sensor is still linear. If the sensitivity is not constant over the range of the sensor, this is called nonlinearity. Usually this is defined by the amount the output differs from ideal behavior over the full range of the sensor. If the deviation is caused by a rapid change of the measured property over time, there is a dynamic error. Often, this behaviour is described with a bode plot showing sensitivity error and phase shift as function of the frequency of a periodic input signal. If the signal is monitored digitally, limitation of the sampling frequency also can cause a dynamic error. Noise is a random deviation of the signal that varies in time. And, surely, sensors may to some extent be sensitive to properties other than the property being measured. For instance, most sensors are influenced by the temperature of their environment.

These deviations can be classified as systematic errors or random errors. Systematic errors can sometimes be compensated for by means of some kind of calibration strategy. Noise is a random error that can be reduced by signal processing, such as filtering, usually at the expense of the dynamic behaviour of the sensor.

The last item to be considered about the sensor is its resolution. The resolution of a sensor is the smallest change it can detect in the quantity that it is measuring. Often in a digital display, the least significant digit will fluctuate indicating that changes of that magnitude are only just resolved. The resolution is related to the precision with which the measurement is made. Thus, a scanning tunneling probe (a fine tip near a surface collects an electron tunneling current) can resolve atoms and molecules.