2. The shell of this meter is made of high-strength aluminum alloy. Inside, an equipotential protection ring and a fourth-order active low-pass filter are installed, which can effectively shield against external power frequency and strong electromagnetic fields. For capacitive test objects, because the output short-circuit current is greater than 1.6mA, it is easy to quickly raise the test voltage to the rated value of the output voltage. For low resistance measurement, due to the proportional method design, voltage drop does not affect the test accuracy.
3. No manual effort is required; it is powered by batteries, and the range can be automatically switched. The clear panel operation and LCD display make measurement very convenient and fast.
4. The output short-circuit current of this meter can be directly measured without estimation under load.
Collecting suitable high-voltage resistors and integrating them into one instrument poses another challenge. This is a safety standard challenge related to the mandatory requirement of EU CE certification, the Low Voltage Directive. The standard relevant to instrument manufacturers is EN 61010 – Safety requirements for electrical equipment for measurement, control, and laboratory use.
The Low Voltage Directive requires limiting the calibrator voltage to 1,000 Vrms. So how to calibrate megohmmeters with test voltages up to 5 kV? Such instruments have a wider dynamic range, can measure resistances up to 10 TΩ, and provide guard terminals as described above, enabling accurate measurement of very high resistance values. Fortunately, this guard configuration can itself form a resistance multiplier, effectively multiplying a known resistance by 1000 times, as shown in the example in Figure 2 [3]. Equally important, since the multiplier is a discrete, isolated, independent device that can meet the high voltage required for the multiplier, it is no longer within the scope of the Low Voltage Directive.
