# Electrical Resistance

Topics: Electrical resistance, Ammeter, Electrical measurements Pages: 3 (644 words) Published: December 2, 2012
JMJ
MARIST BROTHERS
MARIST AVENUE, GENERAL SANTOS CITY

MULTITESTER
Instrumentation and Control
CpE 511

NAME: KURT RUSSEL C. CHUASeptember 01, 2012

INSTRUCTOR: ENGR. JAY S. VILLAN, MEP-EE

Introduction
A multitester or multimeter is a device which can be used to gather data about electrical circuits. A basic multitester can measure resistance, voltage, and continuity; while more advanced versions may be able to provide additional data. This tool can be very useful to have around the house, and anyone who plans on doing electrical repairs should most definitely use a multitester for safety reasons. Multitesters can be used with the current off or on in most cases, although using the device with the current on can sometimes result in damage to the device.

Theory
Ammeters are employed for measuring current in a circuit and connected in series with the circuit. As ammeter is connected in series, the voltage drop across ammeter terminals should be as low as possible. This requires that the resistance of the ammeter should be as low as possible. The current coil of ammeter has low current carrying capacity whereas the current to be measured may be quite high. For this reason a low resistance is connected in parallel to the current coil. Voltmeters are employed to measure the potential difference across any two points of the circuit these are connected in the parallel to the circuit. The resistance of voltmeter is kept very high by connecting a high resistance in series of the voltmeter with the current coil of the instrument. The actual voltage drop across the current coil of the voltmeter is only a fraction of the total voltage applied across the voltmeter which is to be measured. An ohmmeter is a measuring instrument used to measure the resistance placed between its leads. The resistance reading is indicated through a mechanical meter movement...