# Test and Measurement World

## Test and Measurement World Measurements Section

One Stop For Your Test and Measurement Need

## Current measurement vs voltage measurement-Difference between Current measurement and voltage measurement

This page compares current measurement vs voltage measurement and mentions difference between current measurement and voltage measurement. The equipments used for current and voltage measurement are also mentioned.

According to current continuity law, current can be measured in any portion of single loop circuit. It is measured by connecting Ammeter in series.

Voltage is measured across the element through which current is passing. It is measured by connecting Voltmeter across or parallel to the circuit element.

### Current Measurement There are two methods of current measurement viz. contact less method and using Ammeter or Multimeter.

In contact less method, current passing through the element produces magnetic field. This magnetic field generated rotates the indicator of the compass i.e. needle. This contact less method is not very accurate. Moreover it is less sensitive to low value of current and hence used in high value current measurement. The second for current measurement is using Ammeter device. The device uses magnetic field generated by current to deflect the needle as shown. The deflection of needle is proportional to magnitude of magnetic field. This magnetic field is proportional to quantity of electric current passed through it.

In the electric or electronic circuit diagrams, Ammeter is shown as "A letter in the circle".

In order to measure current through the circuit.
• The path is broken and Ammeter is inserted in the path or branch.
• Current through the Ammeter is measured by needle deflection. This is due to the fact that current through resistor or any other circuit element 'X' is same as current passed through the Ammeter.
This current measurement method is applicable for any circuit component and not limited to only resistors in the circuit. The same is shown in the figure-1.

### Voltage Measurement The figure-2 depicts setup used for voltage measurement. To measure voltage we need to probe voltage between two nodes in the circuit. When the voltage is applied to input of instrument i.e. voltmeter, there will be current (Iv) flowing through it. According to charge conservation law, this current (Iv) reduces current through the test circuit element. This results into change in voltage V to be measured. Hence to have voltage measurement accurate, resistance of voltmeter must be much higher compare to element under test.

### Comparison between Ammeter and Voltmeter

➨The resistance (RA) of current meter (i.e. Ammeter) must be much smaller compare to resistance (R) of test element in order to have accurate current measurement. The resistance (RV) of Voltmeter must be much higher compare to resistance (R) of test element as mentioned.

➨Ammeter is connected in series while Voltmeter is connected in parallel to the test element.

➨The current measurement error is given by
ΔI/IM = ( I/IM )-1 = RA/R

The Voltage measurement error is given by
ΔV/VM = ( V/VM )-1 = R/RV

Following are the links to other useful measurements available on Test and Measurement World website.
Difference between EVM vs subcarriers and EVM vs symbols
Current measurement vs Voltage measurement
Inductance measurement vs Capacitance measurement
Difference between Power and Energy measurements
EMC measurement vs EMI measurement
Electric and Magnetic Field Measurements

### What is difference between or comparison between

Following links mention difference or comparison between various equipments:
comparison between VSG and VSA
DIfference between SNA ans VNA
Oscilloscope Bandwidth versus Rise time
Oscilloscope vs Logic Analyzer
Difference between Oscillscope types
Comparison between spectrum and network analyzer