In accordance with DIN EN 60751 section 6.3.1 the insulation resistance between each measuring circuit and the sheath, at a minimum test voltage of 100 V DC, must not be less than 100 MOhm. Should the insulation resistance be too low, a measuring error occurs that causes the display of too low a temperature. In relation to a resistance thermometer (with sheathed cable) this results, with an insulation resistance of 100 kOhm, in a display error up to 0.25 Ohm and at 25 kOhm up to 1 Ohm. On all WIKA resistance thermometers, an insulation test with 500 V DC and an insulation resistance of > 1,000 MOhm is carried out, i.e. we test to a factor of 50 better than specified by the standard.