The insulation resistance test is the second test required by the electrical safety testing standards.The insulation resistance test consists in measuring the insulation resistance of a device under test, while phase and neutral are short circuited together. The measured resistance has to be higher than the indicated limit from the international standards. A megohmmeter (also called insulation resistance tester, teraohmmeter) is then used to measure the ohmic value of an insulator under a direct voltage of great stability. To measure a high value resistance, techniques for measuring a low value current are used. A constant voltage source is applied to the resistance to be measured and the resulting current is read on a highly sensitive ammeter circuit that can display the resistance value. Two types of ammeter circuits are used on our range of insulation resistance tester, each circuit being chosen depending on the resistance values to be measured.