Voltmeter
is a kind of Galvanometer that is used for measuring voltage potential of an
electric circuit or the potential difference between two points. Technically
speaking, all Voltmeters are basically Ammeters, as they measure current
rather than the voltage. Voltage gets measured only when current is
transmitted in a circuit through the resistance. No doubt Voltmeters are
often termed as high resistance Ammeters.
A Voltmeter is a versatile instrument as they are adept in measuring not
only voltage but also current and resistance. This is the reason why
Voltmeter is also known as Multimeter. A Voltmeter can measure voltages of
both direct current (DC) or alternating electric current(AC) . Typical a
Voltmeter scale is graduated in volts, millivolts (1/1000 volt), or
kilovolts (1,000 volts) A laboratory standard Voltmeter employs
electromechanical mechanism for functioning and typically comes with ranges
in between 1000 - 3000 volts (V).
Voltmeter
Design
A Voltmeter circuit is designed to have a high resistance so that it does
not have any significant impact on the voltage as well as current of the
measured circuit. Let's now understand the different aspects of a Voltmeter.
First is the display. This is the place for displaying the results of the
measurements undertaken. Voltmeter may be analog or digital. In case of
analog Voltmeter readings are taken off a scale. While digital Voltmeter
generally comes with LED or LCD display panel for taking voltage measurement
reading. Then there is positive input terminal, and the negative input
terminal.
As a rule, for testing the components, a Voltmeter is connected parallely
in the circuit with them. This is why current flowing through a voltmeter
adds up to the overall current in the circuit being tested. Thus potentially
affecting the voltage that is to be measured. An ideal Voltmeter going
strictly by text book, comprises an infinite resistance, drawing no current
from the circuit being tested. However, this an ideal situation that exists
only in theory.
A voltmeter typically measures the difference of voltage between an
positive input terminal and the negative input terminal of the voltmeter.
While designing Voltmeters, one of the important consideration is to have a
little disturbance on the circuit. This can only be achieved if the
instrument draws minimum current for operation by using sensitive ammeters
or microammeters connected in series with a high resistance.
Choosing a Voltmeter
Selecting a Voltmeter is a challenging task, before narrowing down on the
supplier it is always better to keep abreast of key technical information
regarding them. The following points may prove to be useful.
- The first question is regarding the range that needs to be covered,
for example 10-16 volts.
- Is lighting required in the Voltmeter.
- What is the nature of environment where the Voltmeter will be used
for example high moisture, stationary equipment etc.
- Type of Dial face or pointer to be used in the Voltmeter.
- One of the most important consideration in choosing a right Voltmeter
is the source resistance. Source resistance is of paramount importance
for accurate measurement of the source voltage. Basic Voltmeter models
is founded on the ideal voltmeter standard that is in parallel with an
input resistance. With input resistance exceeding source resistance, the
voltmeter can give fairly precise voltage readings. Sophisticated
Voltmeters takes into consideration other characteristics of a non-ideal
voltmeter.
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Types of Voltmeter
Digital Voltmeters
With
the advent of digital electronic devices, Digital Voltmeters are now in
vogue in most of the physics laboratories. Digital Voltmeters can measure
the current flow in amperes and then display the voltage digitally. The
Digital Voltmeters provide accurate details about current draw and current
continuity thus helping the users to troubleshoot erratic loads and trends.
Modern Digital Voltmeters can They have both positive and negative leads and
feature extremely low internal resistance A digital voltmeter shows voltage
directly as numerals. Some of the new types of Digital Voltmeters can
ascertain voltage readings to several significant figures.
Electrostatic Voltmeters
Electrostatic
Voltmeters are instruments that can effectively measure voltages without any
charge transfer. Electrostatic voltmeters are particularly suitable in cases
where voltage measurements cannot be performed using conventional contacting
voltmeters. Conventional contacting Voltmeters need charge transfer to the
voltmeter, thus leading to loading and adjustment of the source voltage.
Solenoid Voltmeter
A Solenoid voltmeter is a type of voltmeter that is in use mostly by
electricians for testing and debugging of electrical power circuits.
Solenoid voltmeters are known for extreme ruggedness and do not damaged
easily because of rough handling or electrical overload.
Vacuum Tube Voltmeter
A
Vacuum tube Voltmeter is aso known as electronic voltmeter, or vacuum tube
voltmeter (VTVM). Though not in much use a VTVM employs a tube or transistor
circuit for amplifying the input voltage. This facilitates dual objectives.
First it give rise to increased sensitivity, secondly i9t gives rise to
increased input impedance. A Vacuum tube Voltmeter generally has an input
resistance in the range of of 10 to 20 megohms.
Microvoltmeter
Microvoltmeter
is a multipurpose instrument for measuring low DC voltage. These days
Digital Microvoltmeters can measure voltage down to even 1µV. Some of
the exceptional features offered by the latest range of Microvoltmeters
include.
» A low temperature drift
» Automatic polarity indication
» Recorder facility
» 100 % overranging.
» Digital panel meter for better accuracy and convenience
» IC regulated internal power supplies.
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