Product Aliases
Digital megohmmeter, analog megohmmeter, insulation tester, digital high-voltage megohmmeter, high-voltage insulation resistance tester, insulation resistance meter, insulation characteristic tester, motor-driven megger, electronic insulation resistance tester, high-power high-voltage megohmmeter
Features of Megohmmeter
1. High output power, strong load capacity, and strong anti-interference capability.
2. The housing 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 samples, due to the output short-circuit current greater than 1.6mA, it is easy to quickly raise the test voltage to the rated value of the output voltage. For low-resistance measurements, since the proportional method is adopted, voltage drop does not affect the measurement 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 needing to estimate through loaded measurements.
Synthetic Resistance
The method of synthetic resistance is excluded due to design cost and size constraints. Instead, a discrete high-voltage resistor matrix approach is used to form an array that can provide over 500,000 different resistance values. In this calibrator, there are 8 resistance ranges covering from 10 kΩ to 10 GΩ, each range providing a stable 4.5-digit output.
Collecting suitable high-voltage resistors and integrating them into an instrument presents another challenge. This is related to the safety standard challenge of the Low Voltage Directive, a mandatory requirement for CE certification in the EU. The relevant standard for instrument manufacturers is EN 61010 - Safety Requirements for Electrical Equipment for Measurement, Control, and Laboratory Use [2].
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 mentioned above to accurately measure 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]. Importantly, since the multiplier is a discrete, isolated, and independent device that can handle the high voltage required, it is no longer within the scope of the Low Voltage Directive.
