The change in temperature of the receiving element is then measured where is been said in a typical radiation thermopile a number of thermocouples made of very fine strips are connected in series and is arranged side by side, so that all the hot junctions, which are increase the energy absorbing ability, fall within a very small target area.
The thermoelectric characteristics of the thermopiles are very stable because the hot junctions are not above a few hundred degrees celsius, and the thermocouples are not exposed to the atmosphere of the furnace.
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Pyrolectric:
When it been used as a detector in a radiation thermometer, where by the radiation absorbed at the surface of the pyroelectric slice and makes the temperature of the detector to increase to a higher level. At the beginning the charge on the electrodes should have leaked away through the external electrical circuit.
As the plate heats up the voltage is detected between the two electrodes. When the device reaches its temperature, there will be a losing heat to its environment at the same rate as it is receiving heat by radiation, the charge slowly leaks away through the electrical circuit, and the detected voltage becomesto zero. The device will detect the change of radiation.
Photo-electric:
The photoelectric pyrometer operated on the substitution principle having as an external reference source a black-body lamp. The effective wavelength of the system was defined by an interference filter having a maximum transmission at about 660 nm and a bandwidth of 12.5 nm. A black-body cavity enclosed in a stainless steel-clad copper cylinder was set at the temperature of the gold point using a calibrated thermocouple.
The sectored disks used for measuring the energy ratios were calibrated by the time-ratio method which is here described in detail.
A photodiode is used as a semiconductor diode, it is made of germanium or silicon where by both are good semiconducting elements and the diode is constructed in such a way that the incident radiations can reach the junction region of the semiconductor
Optical pyrometer
The temperature of the filament is known from its electrical resistance. Temperature readout is achieved either by a meter measuring the current through the filament or by temperature calibrations on the control resistor regulating the current through the lamp. Lamps for optical thermometers are not normally operated at temperatures much in excess of 1500°C.
Different type of pyrometers
Ratio radiation pyrometers (two colour pyrometers)
This pyrometer measures the reading of the radiated energy of an object between two narrow
wavelength bands and then calculates the ratio of the two energies.
This ratio is the function of the temperature of the object. This is also called as two colour pyrometer because the two wavelengths corresponded to different colors in the visible spectrum.
If the object does not fully cover the spot the output signal will not change the temperature measurement is independent of emissivity.
Working of 2 color pyrometer
Fiber optic radiation pyrometers
Optical pyrometers can be considered a subset of narrow band devices. Fiber optic pyrometers can be classified as wide band, narrow band, or ratio devices.
These devices use an optical fiber (light guide) to direct the radiation to the detector. The spectral response of these fibers is extended to about 2 microns so it is useful in measuring object temperatures to as low 100°C.
An optical head, a glass fiber and a signal processing unit together forms a fiber optic pyrometer. The optical head do not contain any electronics.
Protection circuit
Pre-amplifier
Calibration signal
Lead selector3.
Driver amplifier
Microcomputer
Memory system
Isolation circuit
Protection circuit:
The protection circuit prevents any damage due to high voltages that may appear as inputs to the electrocardiograph.
Lead selector
The lead selector is controlled by an operator or automated, and provides the ability to record from various combinations of the leads connected to the patient.
Calibration signal
Calibrated to 1-mV which is applied to each channel recorded. The output for the calibration signal should be the same for each channel recorded.
Preamplifier
The preamplifier stage consists of a differential amplifier with a high CMRR (common-mode-rejection ratio).
The high CMRR ensures that any potential on the patient's body that is common to both inputs of the differential amplifier is not amplified by the electrocardiograph.
Isolation circuit
Isolation circuit works as a barrier by preventing more than 10 µA of 60-Hz current flowing through the patient to ground even under the fault condition of the patient accidentally coming in contact with 120 V from the power line.
Driver amplifier
Driver amplifier circuitry is ac-coupled and this prevents the output of further amplifier stages from saturating due to the offset in the input signal.
Then it is filtered with an upper corner frequency (3 dB) of 150 Hz and amplified sufficiently so that it can be recorded.
Memory system
It stores the data and the information.
Microcomputer
It works as an analog to digital converter (ADC) to digitize the signal,
1)Electrical activity of the heart is graphically represented (ECG)
A normal heart beat is initiated by a small pulse of electric current. This tiny electric "shock" spreads rapidly in the heart and makes the heart muscle contract It is a way of measuring the electrical impulses that the heart generates as it is beating.
2) The electrical current generated by the heart is conducted through the pairs of electrodes andleads, and is amplified, recorded, and processed by the electrocardiograph.
Electrodes are used for a twelve lead ECG. The electrodes are usually consist of a conducting gel, embedded in the middle of a self adhesive pad onto the cables clip, at times the gel also forms the adhesive.
The ECG sensor detect and measures cardiac wave form generated by electrical activity of the heart muscle. This creates an electrical current that moves through the body and where it will be measured by electrodes that attached to the body skin.
5)
Voltage to frequency converter.
This converters are electronic devices which convert voltage inputs to frequency outputs. They consist of an analog input amplifier, a precision oscillator system, a resistor-capacitor network, and a power supply.
Low drift input amplifiers enable voltage to frequency converters to process small signals where high levels of input resistance. Input amplifiers provide high impedance to positive voltage and low impedance to negative voltage.
Voltage to frequency linearity requires the use of capacitors with low dielectric. The charge balanced voltage to frequency converters provide increased accuracy and linearity, but have higher supply voltage and current requirements.
Voltage to frequency converters can receive alternate current or direct current voltage inputs and output frequencies or can be said as pulse signals by using techniques such as amplitude modulation , pulse width modulation, and frequency modulation.
Some voltage to frequency converters and send outputs to timers, counters, relays, switches, and potentiometers.
Frequency to voltage converter
Frequency to voltage converters are electronic devices that convert current signal inputs to voltage outputs. They include an operational amplifier for simple linear signal processing and a small resistor-capacitor network for removing frequency-dependent ripples. Frequency to voltage converters can receive alternate current and direct current voltages, frequencies and pulses.
Devices with integrated filters allow some signal frequencies to pass while extinction others. Devices with low pass filters allow signals that are below a cutoff frequency to go thru while blocking signals that exceed .
Device specifications for frequency to voltage converters include the number of analog channels and the number of differential channels.
Differential channels, which have two inputs, define the voltage as the signal to process between the two inputs. Other device specifications for frequency to voltage converters include maximum output voltage, accuracy, and signal isolation.
6) Differential pressure flow meters use Bernoulli's equation to measure the flow of fluid in a pipe which is
And the flow rate will be: Q=AV Q=flow rate A = area V = velocity
Orifice plate
An orifice plate is installed in a line that creates a pressure difference as the fluid flows through it. This differential pressure is measured with impulse lines by a differential pressure transmitter which converts into an analogue or digital signal which can be processed to show in a display of the rate of flow.
ii) Venturi flow meter
Venturi Tube is a low pressure drop meter device identifiable by its tapered inlet, tapered outlet and straight, constricted middle section. It offers constant accuracy, low susceptibility to erosion, high-pressure recovery, and installation at any angle from horizontal to vertical.
This device is corrosion resistant and virtually maintenance free, this measurement product performs in a wide variety of applications that include air, steam, gas, water, vapor chemical substances, sludge and slurry applications
iii) Pitot tube
The pitot tube is measured by the fluid flow velocity where by converting the kinetic energy of the flow into potential energy. The pitot tube can also be used to measure the difference between static and dynamic pressure
iv) Nozzle
The flow nozzles are often used as measuring elements for air and gas flow in industrial applications When a gas accelerate through a nozzle the velocity increase and the pressure, the gas density decrease. The maximum velocity is achieved at the throat, at the minimum area, At this point it is not possible to increase the flow by reducing the downstream pressure.
