Syllabus Recording Devices Introduction, Strip chart recorders, Galvanometer recorders, Null balance recorders, Potentiometer type recorders, Bridge type recorders, LVDT type recorders, Circular chart and X Y recorders. Magnetic tape recorders, Direct recording, Frequency modulation recording, Pulse duration modulation recording, Digital tape recording, Ultraviolet recorders. Biomedical recorders, Electro Cardio Graph (ECG), Electroencephalograph, Electromyograph. Noise in reproduction.
RECORDERS Recorder records an electrical or nonelectrical quantities as a function of time. Classified into Analog recorders A) Graphic recorders( Strip Chart Recorders,X-Y recorders) B) Oscilloscopic Recorders C) Magnetic tape recorders Digital recorders A) Incremental B)Synchronous
Galvanometer Type Use D Arsonval galvanometer As the current flows through the coil, it deflects. The deflection is produced by a galvanometer which produces a torque on the account of current passing through the large moving coil situated in a strong magnetic field. Greater the amplitude of the incoming signal (proportional to the quantity being measured), the grater is the deflection. Instrument should be critically damped to avoid overshoot. Does not suitable for fast variations in current,voltage or power. Only records the average value.
GALVANOMETER RECORDER
CIRCULAR CHART RECORDER CIRCULAR CHART RECORDER 1 CIRCULAR CHART RECORDER 2
Null Type Change in input produced by the signal upset the balance of the measuring circuit of the recorder. As a result of this unbalance, an error signal is produced that operates on some devices which restore the balance or bring the system to null conditions. Eg: Potentiometric Recorders, Bridge Recorders, LVDT Eg: Potentiometric Recorders, Bridge Recorders, LVDT Recorders.
SELF BALANCING POTENTIOMETRIC RECORDER
BRIDGE TYPE RECORDER
Strip chart Recorder Advantages: Conversion of data is easier when rectangular coordinated are used. The rate of movement of the chart can easily be changed to spread out the trace of the variable being observed Disadvantages: Observing the behavior several hours or days back is not as easy. 16 November 2017 12
Strip Chart Recorders
X-Y Recorder Records one or more parameters with respect to some other Or x-y recorder is an instrument which gives a graphic record of the relationship between two variables. In some type recorders,pen moves in two axes In X-Y recorders, an emf is plotted as a function of another emf. 16 November 2017 14
X-Y Recorder 16 November 2017 15
X-Y RECORDER X-Y RECORDER
X-Y Recorder A signal enters each of the two channels. The signals are attenuated to the inherent full scale range of the recorder, the signal then passes to a balance circuit where it is compared with an internal reference voltage. The error signal,the difference between the input signal voltage and the reference voltage is fed to a chopper which converts d.c signal to an a.c signal. 16 November 2017 17
X-Y Recorder The signal is then amplified in order to actuate a servomotor which is used to balance the system and hold it in balance as the value of the quantity being recorder changes. 16 November 2017 18
Application X-Y Recorder Speed torque characteristics of motors lift Drag wind tunnel tests Plotting of characteristics of vacuum tubes, zener diodes rectifiers and transistors etc Regulation curves of power supplies Plotting stress-strain curves, hysteresis curves and vibrations amplitude against swept frequency Electrical characteristics of materials such as resistance versus and temperature plotting the output from Electronic calculators and computers 16 November 2017 19
MAGNETIC TAPE RECORDER Magnetic tape recording HEAD Magnetic tape recording Data Storage
TAPE TRANSPORT MECHANISM
Digital Recording An analog signal is converted to digital by an analog-to-digital converter, which measures the amplitude of an analog signal at regular intervals, which are specified by the sample rate, and then stores these sampled & quantized numerical value in computer hardware such as compact disc or hard` disk. Digital recordings are very accurate, the accuracy determined only by the quality of the D/A and A/D converters. For optical disc recording technologies such as CDs or DVDs, a laser is used to burn microscopic holes into the dye layer of the medium. A weaker laser is used to read these signals. This works because the metallic substrate of the disc is reflective, and the unburned dye prevents reflection while the holes in the dye permit it, allowing digital data to be represented.
Digital Recording During digital recording of the analog signal, analog to digital (A/D) conversion takes place from continuous time-amplitude coordinates to discrete time-amplitude coordinates
Digital Recording
PWM
LVDT
LVDT LVDT
ECG
EEG Electroencephalography (EEG) is an electrophysiological monitoring method to record electrical activity of the brain. It is typically noninvasive, with the electrodes placed along the scalp.
EMG Electromyography (EMG) is a diagnostic procedure to assess the health of muscles and the nerve cells that control them (motor neurons). Motor neurons transmit electrical signals that cause muscles to contract. An EMG translates these signals into graphs
EMG An EMG uses tiny devices called electrodes to transmit or detect electrical signals. During a needle EMG, a needle electrode inserted directly into a muscle records the electrical activity in that muscle. A nerve conduction study, another part of an EMG, uses electrodes taped to the skin (surface electrodes) to measure the speed and strength of signals traveling between two or more points. EMG results can reveal nerve dysfunction, muscle dysfunction or problems with nerve-to-muscle signal transmission.
Thanks Prof.Sharanabasappa, EEE Dept, RYMEC A Course in Electronic Measurements and Instrumentation by A.K. Sawhney Electrical and Electronics Measurements and Instrumentation by Prithwiraj Purkait et al Electrical measurements book by P.M.Chandrasekharaiah Electrical Measurement & Measuring Instruments by A.V.Bakshi et al https://en.wikipedia.org/ https://electronics.howstuffworks.com https://www.embeddedadventures.com http://www.electronics-tutorials.ws slideshare.net And other Internet resources