Aim:- To study about various Electrical Measuring Devices.

Materials Required:- Different Measuring Devices like Ammeter, Voltmeter, Ohmmeter, Energy meter etc.

Theory:-

Ammeter:- Ammeter is used for measuring Electric Current. Current is measured using the unit Ampere. There are AC ammeters and DC ammeters which can be used for measuring Alternating Current and Direct Current.

ammeter-250x250      ammeter-digital

Ammeter Usage

PARTS AND MATERIALS

  • 6-volt battery
  • 6-volt incandescent lamp

Basic circuit construction components such as breadboard, terminal strip, and jumper wires are also assumed to be available from now on, leaving only components and materials unique to the project listed under “Parts and Materials.”

LEARNING OBJECTIVES

  • How to measure current with a multimeter
  • How to check a multimeter’s internal fuse
  • Selection of proper meter range

SCHEMATIC DIAGRAM

ammeter usage

ammeter usage1

INSTRUCTIONS

Current is the measure of the rate of electron “flow” in a circuit. It is measured in the unit of the Ampere, simply called “Amp,” (A).

The most common way to measure current in a circuit is to break the circuit open and insert an “ammeter” in series (in-line) with the circuit so that all electrons flowing through the circuit also have to go through the meter. Because measuring current in this manner requires the meter be made part of the circuit, it is a more difficult type of measurement to make than either voltage or resistance.

Some digital meters, like the unit shown in the illustration, have a separate jack to insert the red test lead plug when measuring current. Other meters, like most inexpensive analog meters, use the same jacks for measuring voltage, resistance, and current. Consult your owner’s manual on the particular model of meter you own for details on measuring current.

When an ammeter is placed in series with a circuit, it ideally drops no voltage as current goes through it. In other words, it acts very much like a piece of wire, with very little resistance from one test probe to the other. Consequently, an ammeter will act as a short circuit if placed in parallel (across the terminals of) a substantial source of voltage. If this is done, a surge in current will result, potentially damaging the meter:

Voltmeter:- It is used for measuring voltage or potential difference. There are AC voltmeters and DC voltmeters used for measuring AC voltage and DC voltage.A voltmeter is connected in parallel to a load.

voltmeter             voltmeter-digital

Voltmeter Usage

PARTS AND MATERIALS

  • Multimeter, digital or analog
  • Assorted batteries
  • One light-emitting diode (Radio Shack catalog # 276-026 or equivalent)
  • Small “hobby” motor, permanent-magnet type (Radio Shack catalog # 273-223 or equivalent)
  • Two jumper wires with “alligator clip” ends (Radio Shack catalog # 278-1156, 278-1157, or equivalent)

A multimeter is an electrical instrument capable of measuring voltage, current, and resistance. Digitalmultimeters have numerical displays, like digital clocks, for indicating the quantity of voltage, current, or resistance. Analog multimeters indicate these quantities by means of a moving pointer over a printed scale.

Analog multimeters tend to be less expensive than digital multimeters, and more beneficial as learning tools for the first-time student of electricity. I strongly recommend purchasing an analog multimeter before purchasing a digital multimeter, but to eventually have both in your tool kit for these experiments.

LEARNING OBJECTIVES

  • How to measure voltage
  • Characteristics of voltage: existing between two points
  • Selection of proper meter range

ILLUSTRATION

voltmeter usage.png

Voltage is the measure of electrical “push” ready to motivate electrons to move through a conductor. In scientific terms, it is the specific energy per unit charge, mathematically defined as joules per coulomb. It is analogous to pressure in a fluid system: the force that moves fluid through a pipe, and is measured in the unit of the Volt (V).

Your multimeter should come with some basic instructions. Read them well! If your multimeter is digital, it will require a small battery to operate. If it is analog, it does not need a battery to measure voltage.

Some digital multimeters are autoranging. An autoranging meter has only a few selector switch (dial) positions. Manual-ranging meters have several different selector positions for each basic quantity: several for voltage, several for current, and several for resistance. Autoranging is usually found on only the more expensive digital meters, and is to manual ranging as an automatic transmission is to a manual transmission in a car. An autoranging meter “shifts gears” automatically to find the best measurement range to display the particular quantity being measured.

Set your multimeter’s selector switch to the highest-value “DC volt” position available. Autoranging multimeters may only have a single position for DC voltage, in which case you need to set the switch to that one position. Touch the red test probe to the positive (+) side of a battery, and the black test probe to the negative (-) side of the same battery. The meter should now provide you with some sort of indication. Reverse the test probe connections to the battery if the meter’s indication is negative (on an analog meter, a negative value is indicated by the pointer deflecting left instead of right).

If your meter is a manual-range type, and the selector switch has been set to a high-range position, the indication will be small. Move the selector switch to the next lower DC voltage range setting and reconnect to the battery. The indication should be stronger now, as indicated by a greater deflection of the analog meter pointer (needle), or more active digits on the digital meter display. For the best results, move the selector switch to the lowest-range setting that does not “over-range” the meter. An over-ranged analog meter is said to be “pegged,” as the needle will be forced all the way to the right-hand side of the scale, past the full-range scale value. An over-ranged digital meter sometimes displays the letters “OL”, or a series of dashed lines. This indication is manufacturer-specific.

What happens if you only touch one meter test probe to one end of a battery? How does the meter have to connect to the battery in order to provide an indication? What does this tell us about voltmeter use and the nature of voltage? Is there such a thing as voltage “at” a single point?

Be sure to measure more than one size of battery, and learn how to select the best voltage range on the multimeter to give you maximum indication without over-ranging.

Now switch your multimeter to the lowest DC voltage range available, and touch the meter’s test probes to the terminals (wire leads) of the light-emitting diode (LED). An LED is designed to produce light when powered by a small amount of electricity, but LEDs also happen to generate DC voltage when exposed to light, somewhat like a solar cell. Point the LED toward a bright source of light with your multimeter connected to it, and note the meter’s indication:

Batteries develop electrical voltage through chemical reactions. When a battery “dies,” it has exhausted its original store of chemical “fuel.” The LED, however, does not rely on an internal “fuel” to generate voltage; rather, it converts optical energy into electrical energy. So long as there is light to illuminate the LED, it will produce voltage.

Another source of voltage through energy conversion a generator. The small electric motor specified in the “Parts and Materials” list functions as an electrical generator if its shaft is turned by a mechanical force. Connect your voltmeter (your multimeter, set to the “volt” function) to the motor’s terminals just as you connected it to the LED’s terminals, and spin the shaft with your fingers. The meter should indicate voltage by means of needle deflection (analog) or numerical readout (digital).

If you find it difficult to maintain both meter test probes in connection with the motor’s terminals while simultaneously spinning the shaft with your fingers, you may use alligator clip “jumper” wires like this:
Determine the relationship between voltage and generator shaft speed? Reverse the generator’s direction of rotation and note the change in meter indication. When you reverse shaft rotation, you change the polarity of the voltage created by the generator. The voltmeter indicates polarity by direction of needle direction (analog) or sign of numerical indication (digital). When the red test lead is positive (+) and the black test lead negative (-), the meter will register voltage in the normal direction. If the applied voltage is of the reverse polarity (negative on red and positive on black), the meter will indicate “backwards.”

Ohm meter:-  It is used for measuring resistance . Unit for measuring resistance is Ohms.(Ω).

ohm-meter-analog

Energy Meter:- It is used for measuring energy consumption in Domestic and Industrial sectors. The unit for measuring the Electrical Energy is KWH.(Kilo Watt Hour).

energy-meter-analog              energy-meter-digital

Measure Electric Current

How to Measure Electric Current, Voltge and Resistance in a  circuit using Multimeter