In electrical installation resistance matters as much as conductivity. Since this is the case measuring the amount of resistance an insulator provides is necessary to keep everything running smoothly. This is where a Megger resistance test is performed by a Megger device which is also known as a resistance measuring device. A Megger resistance test essentially works by sending out a high DC voltage to the insulator to measure the level of resistance it can provide. In order to perform this test, a Megger device must be hooked up to the installation or machine winding which is why Megger devices are portable. Also, different installations are used in different appliances and settings as those for your household and industrial plants are not the same. This is why there are different types of Megger resistance tests. Types of Resistance Tests Time-Resistance Method A time-resistance method is based on the absorption effect of good insulation compared to that of contaminated insulation. This is a fairly independent Megger test when it comes to temperature as it can provide definitive results without the need for prior tests. Note that each test varies with results as each one is meant to be used in a specific scenario. Short-Time Test Also known as a spot-reading test, a short-time resistance test is done by connecting the Megger resistance tester across the insulation that is tested. Usually, this Megger test lasts about 60 seconds, hence the name. Unlike the time-resistance method, during the short-time test humidity, temperature and the condition of the insulation can affect the reading. Dielectric Absorption Ratio With a dielectric absorption ratio test, you are essentially getting two-time readings from the same insulation during the same time frame as the one on a short-time test. During 60 seconds of testing, the tester will divide the test into two half. Essential a dielectric absorption ratio test takes will two readings each at a 30-second interval. With a dielectric absorption ratio, you get two readings one at every 30 seconds which makes it a more accurate test since you can compare both readings. Types of Meggers Analog If you like to look at a pointer and a scale then analog Megger devices are for you. They do rely on a simpler operation and are not as reliant on batteries which makes them more independent. But analog Meggers are not as reliable or as accurate as their digital counterparts. Analog Megger testers are also a lot more affordable than digital ones as they do not require an external source in order to operate. Some people have analog and digital testers with the analog being a backup option. This is useful for when the digital or electronic tester encounters some issues that cannot happen on an analog device Digital With a digital Megger insulation tester, you will definitely need to charge the device to keep it running but you will get a lot more in return. Not only will you forget about squinting your eyes to see the numbers on the dial but you will also get readings a lot faster and with a lot more information too. Digital Meggers can also be devices with dot-matrix displays but no battery dependencies. These are something between an analog and a true digital (electrical) resistance tester. A digital Megger can be automated too as they only have two connecting leads through which they produce current and voltage. All you need to do is press a button and the test commences and then you just get the information on the screen once the test is done. Digital Megger testers are far more convenient as you don't have to manually set up, the device does this for you. Megohmmeter vs Insulation Tester You might think that Megohmmeters and insulation testers are the same because they do the same thing. Well, that may be true on a basic level, when it comes to performing far more complex tests an insulation tester is far better. Why? Because insulation testers unlike Megohmmeters can measure voltage and current alongside resistance. A Megohmmeter can only measure resistance values by sending a high voltage signal into the object that you're testing. This doesn't mean you have to get an insulation tester if you don't need one. Although it's more capable it's not always a more suitable solution. Conclusion
No matter how advanced or how basic your Megger tester is it will still be able to provide you with a proper reading as long as you look after it. No Megger device is going to make you a better electrician as the device itself only serves to provide you with information about a system's or device's resistance. What you do with the information and how you interpret it is up to you. You don't always need to go for the most expensive device a reasonably priced resistance tester will be more than enough.
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