Difference Between Ohmmeter And Avometer
written by Adeel AbbasThere is a difference between ohmmeter and avometer. The ohmmeter is used to measure the resistance and avometer is used to measure electric current, potential difference, and resistance.
Ohmmeter
A device used for rapid measurement of resistance is called an Ohmmeter.
Construction of ohmmeter
It consists of a galvanometer variable a resistance of rs known value and a cell connected in series. The resistance R which is to be measured is connected between terminals c and d.
Working of ohmmeter
The series resistance, rs is so adjusted that when terminals c and d are short-circuited then R=0. The galvanometer gives full-scale deflection and on the scale of a galvanometer, it is marked as 0.
Similarly when terminals c and d are open, no current passes through the galvanometer and it shows zero deflection Thus zero of the scale is marked as infinity. For any other value of R. galvanometer deflects to some intermediate point and hence the galvanometer scale can be calibrated to read the resistance directly.
Avometer or Multimeter
An instrument that is used to measure current in amperes, potential difference volts and resistance in Ohms is called the AVO meter.
Construction of Avometer
Basically, an AVO meter consists of a sensitive moving Coil galvanometer. It is converted into a multi-range ammeter, voltmeter, or ohmmeter according as a current measuring circuit or a voltage measuring circuit, or resistance measuring circuit is connected with the galvanometer with the help of a switch known as function selector FS.
The main terminals of an AVO meter are X and Y, which are connected with the circuit whose measurement is required.
Voltage measuring part of avo meter
It is a multi-range voltmeter that consists of a number of resistances. These resistances are connected in series with the moving coil galvanometer with the help of a switch called the ‘Range Switch’. The value of each resistance depends upon the range of the voltmeter.
Thus greater the series resistances, the greater will be the voltage range. AVO meter also measures the alternating voltage. The AC voltage is first converted into DC voltage by rectification and then measured.
Current measuring part of avo meter
It is actually a multi-range ammeter that consists of a number of low resistances connected in parallel with a galvanometer. The value of these resistances depends upon the range of the ammeter. The circuit has also a range selection switch SR which is used to select a particular range of the current.
Resistance Measuring Part Of Avo Meter
It is a multi-range Ohm meter. It consists of a battery of EMF Vo a variable resistance, rs connected in series with galvanometer of resistance Rg. When the function switch is switched to position X3, then the circuit is connected with X Y terminals of the AVO meter. Before measuring any resistance Ohmmeter is first zeroed X and Y terminals are short-circuited and rs is so adjusted to get full-scale deflection.
Digital Multimeter
An electronic instrument that is used to measure the current voltage and resistance is called a digital multimeter. It is a digital version of an AVO meter. It is a very popular testing device because the digital values are displayed automatically with a decimal point, polarity, and unit for V, A, or Ω.
These meters are easier to use because they eliminate the human error that often occurs in reading the dial of an ordinary AVO meter.
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