The Measurement And Instrumentation Engineering Essay
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Published: Mon, 5 Dec 2016
A pyrometer is used to measure the temperature of an object from a distance, without making contact. The method used for making these non-contacting temperature measurements is known as radiation pyrometry. Non-contact temperature sensors use the concept of infrared radiant energy to measure the temperature of objects from a distance. After determining the wavelength of the energy being emitted by an object, the sensor can use integrated equations that take into account the body’s material and surface qualities to determine its temperature Pyrometer is derived from the Greek root pyro, meaning fire. The term pyrometer was originally used to denote a device capable of measuring temperatures of objects above incandescence, objects bright to the human eye. The original pyrometers were non-contacting optical devices which intercepted and evaluated the visible radiation emitted by glowing objects. A modern and more correct definition would be any non-contacting device intercepting and measuring thermal radiation emitted from an object to determine surface temperature. Thermometer, also from a Greek root thermos, signifying hot, is used to describe a wide assortment of devices used to measure temperature. Thus a pyrometer is a type of thermometer. The designation radiation thermometer has evolved over the past decade as an alternative to pyrometer. Therefore the terms pyrometer and radiation thermometer are used interchangeably by many references.
A radiation thermometer, in very simple terms, consists of an optical system and detector. The optical system focuses the energy emitted by an object onto the detector, which is sensitive to the radiation. The output of the detector is proportional to the amount of energy radiated by the target object (less the amount absorbed by the optical system), and the response of the detector to the specific radiation wavelengths. This output can be used to infer the objects temperature. The emittivity, or emittance, of the object is an important variable in converting the detector output into an accurate temperature signal.
Pyroelectric detectors for thermal radiations are a relatively new form of pyrmometers. The construction material is usually ceramics are materials whose molecules have a permanent electric dipole because of the position of the electrons in molecules. Normally these molecules lie in a random “mish-mash” manner all across the bulk of the material hence there is no net electrification as a whole. Also, at ambient temperatures the location or orientation of these molecules is more or less fixed. If the temperature is raised above some level characteristic to the particular material, the molecules start to rotate freely. The temperature at which this start to happen is called the Curie temperature.
When the pyroelectric surface is used as detector in a pyrometer, when the radiations from the source are absorbed by the pyroelectric material, its surface temperature increases .In the beginning the charge on the electrodes would be leaked away through the external electrical circuit and hence the measured voltage between the electrodes would be zero. When the pyroelectric surface heats up a voltage is detected between the two electrodes. As the temperature is further increased, further voltage is increased. Through this voltage value we can measure the temperature. The physical construction of a pyroelectric pyrometer is similar to the total radiation thermometer.
Pyroelectric linear arrays
A photoelectric pyrometer has been developed with which the International Practical Temperature Scale (IPTS) above the gold point, 1063 °C, is realized about 5 times more accurately than with the prevalently used disappearing filament visual pyrometer. Estimated standard deviation uncertainties of realizing the IPTS with the photoelectric instrument.An instrument that measures high temperatures by using a photoelectric arrangement to measure the radiant energy given off by the heated object.
Optical system of an automatic photoelectric pyrometer:
An optical pyrometer is a device which allows contactless temperature measuring by using the incandescense color. It is based upon the fact that all black bodies do have the same incandescense color at a given temperature. It is very straightforward and allows any temperature from which a hot object emits light ( > 500 deg C). It is made from a small magnifying optical device (like a monocular or very small telescope) in which a small incandescent bulb is placed which image is sharp when the user views through the eyepiece (the lens(es) on the eye end of the optical device). The background is the hot object to be gauged. The electrical current flowing through the filaments in the bulb is an indication of their temperature. This current is controlled by a potentiometer which is put between the power source (a battery) and the bulb. An ammeter is used to display the temperature. Its range is from 500 C (== 900F lower limit when an object incandesces) to 1600 C (3000 F), which is suitable for most applications.
Typical temperature ranges for optical pyrometers
ECG (electrocardiogram) is a test that measures the electrical activity of the heart. The heart is a muscular organ that beats in rhythm to pump the blood through the body.
The signals that make the heart’s muscle fibers contract come from the sinoatrial node, which is the natural pacemaker of the heart.
In an ECG test, the electrical impulses made while the heart is beating are recorded and usually shown on a piece of paper.
This is known as an electrocardiogram, and records any problems with the heart’s rhythm, and the conduction of the heart beat through the heart which may be affected by underlying heart disease.
Block diagram of ECG
What (Electrically) is being measured??
The measuring can be different with being different type conditions. Usually the some ECG will be recorded when the patient remain resting. But in some case as, some patients who having coronary heart disease symptoms, ECG will be taken while the doing exercise bike or treadmill. The electric waves in the heart are recorded in mill volts by the ECG. The waves are recorded by electrodes positioned on certain parts of the body. Each electrode controls an ink needle that writes on a grid paper. The higher the intensity of the electric wave, the higher up the needle will move on the paper. The paper moves at a certain speed beneath the needle, resulting in an ink curve.
How is electric signal capture? How does it work?
The amplifier receives the electrical signals from the electrodes and converts the information. Because the body’s electrical signals are relatively weak, the amplifier must first stabilize the signal and then amplify by a factor of between five and 10. The amplifier is composed of several sections, including a buffer amplifier and preamplifier — both of which work to convert the information received from the electrodes into information that is strong enough to be read by the output device. The amplifier is designed to receive information directly from the patient; however, it is also separate from the primary power circuits of the ECG machine.
What is the sensor?
Measurement of the ECG signal gets challenging due to the presence of the large DC offset and various interference signals. This potential can be up to 300mV for a typical electrode. The interference signals include the 50-/60-Hz interference from the power supplies, motion artifacts due to patient movement, radio frequency interference from electro-surgery equipments, defibrillation pulses, pace maker pulses, other monitoring equipment, etc.
Depending on the end equipment, different accuracies will be needed in an ECG:
Standard monitoring needs frequencies between 0.05-30 Hz
Diagnostic monitoring needs frequencies from 0.05-1000 Hz
Some of the 50Hz/60Hz common mode interference can be cancelled with a high-input-impedance instrumentation amplifier (INA), which removes the AC line noise common to both inputs. To further reject line power noise, the signal is inverted and driven back into the patient through the right leg by an amplifier. Only a few micro amps or less are required to achieve significant CMR improvement and stay within the UL544 limit. In addition, 50/60Hz digital notch filters are used to reduce this interference further.
Complete circuit of Block diagram
Vout = R3 (V2-V1) When Vout = 0,
0 = R3 (V2 – 1)
V2 = 1 When Vout = 10,
Vout = R3 (V2 – V1)
10 =R3(5 – 1)
10 = 4R3
10R1=4R3 Let R1= 10Kâ„¦
10 Ã- 10K= 4R3
R3 = 25Kâ„¦
R3 = R4 = 25Kâ„¦
R1 = 10
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Voltage to frequency
The family of voltage-to-frequency converters ideally suitable for in simple low-cost-circuits for analog-to-digital conversion, precision frequency-to-voltage conversion, long-term integration, linear frequency modulation or demodulation, and many more. The output when used a voltage-to frequency converter is a pulse train at a frequency precisely proportional to the applied input voltage. Consequently, it provides all the inherent advantages of the voltage-to-frequency converter techniques, and easy to apply in all standard voltage-to-frequency converter application.
Frequency and Voltage
The tachometer uses a charge pump technique and offer frequency repetition for low wrinkle, full input protection in two versions and output swing to ground for a zero frequency input.
The amplitude is fully well-matched with the tachometer and has a floating transistor as its output. This characteristic allows either a ground or supply referred load up to 50mA. This version is well suited for single speed or frequency switching or fully buffered frequency to voltage conversion application.
An obstruction (orifice) is placed in a pipe filled with fluid. The pressure of the fluid is measured at two different points: 1) just upstream of the orifice and, 2) close to the contraction of the fluid (vena contracta). The difference in these two pressures is known as differential pressure. The differential pressure across an obstruction (orifice) in a pipe of fluid is proportional to the square of the velocity of the fluid.
Many factors associated with the pipe, orifice and fluid affect the measurement. Satisfactory measurement requires steady-state, homogeneous, turbulent flowing fluids. Other properties which affect the measurement include: the ratio of pipe diameter to orifice diameter and the density, temperature, compressibility and viscosity of the fluid.
Venturi has a long history of uses in many applications. Due to its simplicity and dependability, the Venturi is among the most common flowmeters. With no moving parts or abrupt flow restrictions, the Venturi can measure fluid flowrates with a minimal total pressure loss.
The principle behind the operation of the Venturiflowmeter is the Bernoulli Effect. The Venturi measures a fluid’s flowrate by reducing the cross sectional flow area in the flow path and generating a pressure difference. After the pressure difference is generated, the fluid is passed through a pressure recovery exit section where up to 80% of the differential pressure generated at the throat is recovered. The pressure differential follows Bernoulli’s Equation.
A NOZZLE IS A DUCT WHICH CONVERT HEAT ENERGY INTO KINETIC ENERGY.IT INCREASES VELOCITY OF FLUID PASSING THROUGH IT AT THE EXPENCE OF PRESSURE
Pitot tube is used for measuring the stagnation within a channel, pipe or duct flow. Pitot tube is made in symmetrical body such as cylinder, cone, or hemisphere with drilled by the side of its central axis. If this is associated with its central axis in the direction of the flow the fluid will accelerate around the upstream face with less energy losses, and a stagnation point incline at the piezometric opening.
Flow measurement using (a) Pitot tube, and (b) Pitot-static tube.
Pitot tubes on aircraft commonly have heating elements called Pitot heat to prevent the tube from becoming clogged with ice.
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