PDF | On May 16, , Ramaprasad Panda and others published Electrical & Electronics Measurements & Measuring Instruments. Electrical and Electronics. Measurements and Instrumentation. Prithwiraj Purkait. Professor. Department of Electrical Engineering and. Dean, School of. CLASS NOTES ON ELECTRICAL MEASUREMENTS & INSTRUMENTATION 2. DISCLAIMER. This document does not claim any originality and cannot .
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Electrical Measurements and Measuring Instruments.pdf - Ebook download as PDF File .pdf), Text File .txt) or read book online. Instrumentation book. instruments and connections, and to understand and minimize sources of error. Furthermore, we will discuss selected electrical measurement methods used to. a measurement system is the degree of closeness of measurements of .. ISI mark on measuring instruments and items so that these may be compared with.
Errors may also occur due to incorrect adjustments of instruments and computational mistakes. These errors cannot be treated mathematically. The complete elimination of gross errors is not possible, but one can minimize them. Some errors are easily detected while others may be elusive.
One of the basic gross errors that occur frequently is the improper use of an Instrument the error can be minimized by taking proper care in reading and recording the measurement parameter. In general, indicating instruments change ambient conditions to some extent when connected into a complete circuit.
Systematic Errors These errors occur due to shortcomings of, the instrument, such as defective or worn parts, or ageing or effects of the environment on the instrument.
These errors are sometimes referred to as bias, and they influence all measurements of a quantity alike. A constant uniform deviation of the operation of an instrument is known as a systematic error. There are basically three types of systematic errors i Instrumental, ii Environmental, and iii Observational i Instrumental Errors Instrumental errors are inherent in measuring instruments, because of their mechanical structure.
For example, in the D'Arsonval movement friction in the bearings of various moving components, irregular spring tensions, stretching of the spring or reduction in tension due to improper handling or over loading of the instrument. Instrumental errors can be avoided by a Selecting a suitable instrument for the particular measurement applications. These errors can also be avoided by i air conditioning, ii hermetically sealing certain components in the instruments, and iii using magnetic shields.
The most common error is the parallax error introduced in reading a meter scale, and the error of estimation when obtaining a reading from a meter scale.
For example, an observer may always introduce an error by consistently holding his head too far to the left while reading a needle and scale reading. In general, systematic errors can also be subdivided into static and dynamic Errors. Static errors are caused by limitations of the measuring device or the physical laws governing its behavior. Dynamic errors are caused by the instrument not responding fast enough to follow the changes in a measured variable. What is the method used to calculate the errors in an instrument?
It involves connecting a measuring instrument into the system under consideration and observing the resulting response on the instrument. The measurement thus obtained is a quantitative measure of the so-called "true value" since it is very difficult to define the true value, the term "expected value" is used.
Any measurement is affected by many variables; therefore the results rarely reflect the expected value. For example, connecting a measuring instrument into the circuit under consideration always disturbs changes the circuit, causing the measurement to differ from the expected value. Some factors that affect the measurements are related to the measuring instruments themselves.
Other factors are related to the person using the instrument. The degree to which a measurement nears the expected value is expressed in terms of the error of measurement. Error may be expressed either as absolute or as percentage of error. Describe the function of the DC-Voltmeter and multi range voltmeter and explain their operation? Ans: DC-Voltmeter A basic D'Arsonval movement can be converted into a dc voltmeter by adding a series resistor known as multiplier, as shown in the figure.
The function of the multiplier is to limit the current through the movement so that the current does not exceed the full scale deflection value. A dc voltmeter measures the potential difference between two points in a dc circuit or a circuit component.
To measure the potential difference between two points in a dc circuit or a circuit component, a dc voltmeter is always connected across them with the proper polarity.
The value of the multiplier required is calculated as follows. Im: full scale deflection current of the movement Rm : internal resistance of movement Rs : Multiplier resistance V: full range voltage of the instrument From the circuit of Fig.
The above equation is also used to further extend the range in DC voltmeter'. Fig 4. In range selector selects the This arrangement is advantageous compared to the previous one, because all multi1llier resistances except the first have the standard resistance value and are also easily available in precision tolerances.
The first resistor or low range multiplier, R4, is the only special resistor which has to be specially manufactured to meet the circuit requirements. Explain the working of solid state voltmeter?
This is a directly coupled very high gain amplifier.
Electrical Measurements and Measuring Instruments
The 0. A 10 k potentiometer is connected between these two offset null terminals with its centre tap connected to a - 5V supply. This potentiometer is called zero set and is used for adjusting zero output for zero input conditions. The two diodes used are for IC protection. Under normal conditions, they are non-conducting, as the maximum voltage across them is l0 mV.
If an excessive voltage, say more than mV appears across them, then depending upon the polarity of the voltage, one of the diodes conducts and protects the IC. A A scale of 50 - A full scale deflection can be used as an indicator. Ro is adjusted to get maximum full scale deflection.
Trainer kit 2. CRO 3. Head phone 4.
Patch cords 5. Digital multimeter Procedure: 1. See that the supply indicator glows. Observe sine wave of frequency 1 KHz at the respective terminals.
Connect jumper links to connect the 1 KHz oscillator to the bridge.
Select one of the multiplier arms by connecting dotted line as shown in figure. Connect CRO between ground and multiplier arm as shown in figure by dotted lines. Connect output of the bridge as an input to the director and connect head phone at the output of the director. At null point you will hear minimum or no sound. Null Point: The waveform observed on CRO decreases when pot moved in any one direction for example if it is moved in clockwise direction then the amplitude of the waveform on CRO decreased and a point is reached where it is maximum.
If the pot is further isolated in the same direction then that amplitude increased again. The minimum point is called the null point. The null point does not mean that amplitude is zero but minimum. Again adjust With P2 to get the exact null position. If null point is not achieved with multiplier arm of ohms then change the multiplier arm to next position till you gets the exact null point.
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Once exact null position is achieved remove all connections switch OFF the unit. Digital multimeter 4.
Probes Procedure: 1. Select any multimeter arm Rmul , for example say E. Connect the require supply to the unit and switch ON the unit. See that the supply inductor glows. Connect CRO at the other two junction of the bridge i.
Now slowly adjust with P2 by moving it either clockwise or anti-clockwise as required such that null point is achieved on CRO. Null Point: The waveform observed on CRO decreases when pot moved in any one direction for example if it is moved in clockwise direction then the amplitude of the waveform on CRO decreased and a point is reached where it is minimum. If null point is not achieved with multiplier arm of E change the multiplier arm to next position till you gets the exact null point.
Measure and not the following with DMM.
Change the value of unknown inductance and repeat the above procedure. Instate of connecting the CRO for observing the null point, that the detector circuit provided in the kit can also be used for finding the null point. To the input terminal. Select one of the pot capacitor from capacitor pot. Electrical Measurements And measuring instruments Page 10 If null point is not achieved with multiplier arm of 1K then change the multiplier arm to next position till you gets the exact null point.
Trainer Kit. Unknown values of capacitors. Head Phone or CRO. Patch Cords 5. Digital Multimeter DMM.
Procedure: 1. Connect jumper links to connect the 1KHz oscillator to the bridge. Connect unknown capacitance of say 0. Select any multiplier arm Rm for example say 1K. Connect the required supply to the unit and switch ON the unit. Connect CRO at the other junction of the bridge i. Now study adjust P1 by moving it either clockwise or anti - clockwise as required, such that null point is achieved on CRO.
Electrical Measurements and Measuring Instruments.pdf
Null Point: The waveform observed on CRO decreases when pot moved in any one direction for example if it is moved in clockwise direction then the amplitude of the waveform on CRO decreases and a point is reached where it is maximum.Describe the function of the DC-Voltmeter and multi range voltmeter and explain their operation? Primary sensing element, which senses the quantity under measurement.
Fig 4. In range selector selects the This arrangement is advantageous compared to the previous one, because all multi1llier resistances except the first have the standard resistance value and are also easily available in precision tolerances.
Describe the function of the DC-Voltmeter and multi range voltmeter and explain their operation? Again adjust With P2 to get the exact null position. Connect the require supply to the unit and switch ON the unit.
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