Converters in Measurement - Sensors

To the input of the A/D converter, analog signal that brought the consequences of observing a phenomenon, it is necessary to convert the values of temperature, pressure, or other physical or chemical process into an analog signal. Such transducers are called Converters in Measurement or SENSOR. So used to convert non-electrical quantities in an electrical voltage.

There are many performance transducers. But they all basically contain the basic electronic components such as:

• Thermistors
  Resistors whose values changed by changing the temperature. Prepared as NTC and PTC resistors. First resistance with increasing temperature is falling and others rising. Incorporated in the circuit with a voltage source and resistant if the divisor should provide a good amplifier temperature sensor.
• Coal-Pressure resistors
  They work on the principle of compacting carbon dust grains. The most famous product is known as a microphone in the telephone handset. But in measuring purposes rather used carbon tiles arranged in a pillar, where the total value of resistance decreases as the pressure on the pole higher. So, have a task to convert the pressure forces the analog signal.
• Measuring potentiometer
  Wired or coal-ply potentiometers have long been known in the electronics and application in daily life. Prepared as resistant wire or carbon layer circular or spiral pattern along which the slider reads voltage across the junction slider that is mechanically connected to a rotating shaft mounted along the axis of the spiral potentiometer. So, turn rotary motion into an analog signal. On these principles for known players joystick.
• Strain gauge
  Stretching resistant wire it becomes thinner and longer, and it is thus changing the resistance. If any man is in fact within the elastic limit of material on the cessation of stretching wire resistance value assumes the original size. It is usually made as more parallel wire elements in series is firmly embedded in a plastic strip. If such a tape sticks to a building or part of the machine hard glue can be traced stretching or twisting, or mechanical loading. In applying commonly used in scales.
• Inductive transducers
  If the coil is inserted moving magnet, or vice versa, every mutual offset coil and magnet induces a voltage in the coil. What are the changes more quickly induced voltage is higher. This principle is used for measuring vibration and acceleration, or speed. So the principle similar to the work of magnetic heads in tape recorders. Will be used in the speed control circuits and the like.
• Capacitive transducers
  The very qualities that the capacitors on it changes the voltage and the junction with the resistant divider connected to an alternating current generator, but indicates that they will serve in the sensors to monitor the frequency changes. This property will be used in probes for monitoring liquid levels in tanks, control rooms and the like. Vari-cap diode larger mentioned.
• Photo-Elements
  Have the property that they are changing the luminous intensity changes resistance. They are available as photo resist, photo-diode or photo-transistor. In combination with a light source will be used by counting objects to the control room.
• Piezo-electric transducers
  Property quartz or titan that of bending on opposite surfaces generates different amount of charge and therefore the potential difference, and conversely that the potential difference caused by mechanical bending characteristic of these converters. Used to track the rapid alternating changes.
• Magnetic transducers
  Prepared as resistors that change value depending on the magnetic field strength. This includes magnetic diodes and Hal generator to an active element like quartz crystals.
• Thermo-electric elements
  Two welded wires of different materials during heating of the connected voltage is given at the end. Another transducer to monitor temperature changes.

Some physical size or condition can be directly expressed in a digital way. For example, monitoring closed the door to the room or the light switch in the vehicle when you open the door. For this purpose, it can also serve plain switch. Such as it is difficult to call them the sensor.

So sensors will generally provide an analog output. Of them are basically required to have no effect on the properties and behavior of the environment in which they are located. The sensor is trying to get their output signal proportional to the physical quantity measured with minimal influence on the same.

Characteristics that should be taken into account when using the sensor accuracy, the ability of approaching the true value of physical size, which is reflected in the following parameters:

• Static error - The deviation between the indicated and actual values of physical size when this does not change. It is usually given as a percentage of the maximum value that can be measured.
• Dynamic error - How many sensor 'late' to change the physical size. Each sensor has a dynamic error. This error vanishes when it is physical size stops changing.
• Repeatability error - The maximum deviation from the mean value the repeated measurements unchanged physical parameters (hysteresis).
• Response time - Represents the time required to change the physical size and begin to express the output from the sensor.
• Dead zone - The biggest change in physical size to which the output from the sensor still does not detect the change.

Of the sensors to be used depends on the type of process to be monitored. The foregoing are only part of the potential to be used in practice. Is estimated that today there are over 10'000 types of sensors covering more than 100 different parameters. There is some kind of special sensory technology, but each kind and each of sensor have something specific. In very demanding analyzes and research will only be used above sensors, but they will be part of an analyzer that will deliver their results counted by the A/D converter. These analyzers are typically very expensive devices renowned companies and are almost unavoidable in the study of chemical processes.

The process technology is very often need different measurements such as pH - measurement for determining the acidity of liquids, gas ionization measurement of humidity, porosity, control of the air, where they will be so complex apparatus used.

Each sensor should be calibrated before use. Calibration is a procedure when the sensor readings engineered to results from a trusted and very precise in purpose related sensors regarding the establishment of its accuracy. Calibration process is carried out by different methods, and not the subject of this area.

Example III

Some kind of sensor has definitely become an integral part of most electronic devices we use. Should not be viewed as any electronic device. Modern car has many sensors in the engine and other parts of the vehicle to monitor the amount of fuel in the tank, engine oil level, condition of brakes, coolant temperature, ambient temperature, and it is a great deal. When the user comes into service, cable service via a special connector sensor connected to a computer running the service and immediately get fairly accurate information about the state of the vehicle.

However, the sensor installed in the home or the waiters helped the following picture is somewhat unusual.

Figure 7.1.4 Use of pressure sensor.

Any pressure when opening beer or wine bottles increases the numerical amount on display for one. Useful for waiters, and for those who want their unusual hobbies have it under control.

SUMMARY:

As there are multiple types of hardware structures in which the transducer can be installed, typically Compatible PC or Apple Macintosh, the type of operating systems and processors, and serial, parallel, USB or PCMCI port if the sensor is connected to the computer via one of the standard connections, care should be taken purchase-transmitter system that anticipates installed. Of course, the device must be obtained:

• Control software (driver) for OS of computer.
• Software for monitoring input measured data and their analysis.

When selecting the measurement system is economical to use multichannel system if it intends to use in various applications simultaneously, as well considering the price of the system if you choose a single channel will serve only one task for a long period of time.

Technology advances, especially in the production of integrated circuits has enabled the creation of handy universal instruments that have built-in A/D converters, and memory in which can store a number of data and program support that will enable reading memory and transfer data to the PC. Such devices are quite sufficient for preliminary measurements or to collect baseline data on the ground. Can be obtained for as little as $ 200.

Producers for the experts have a very diverse range of equipment and sensors, so that when engaging in the selection of the same should have proper knowledge about the values that are obtained by measuring the analogy, they choose the measuring equipment. Wrong judgment can mean wasted resources.