At that point, the display started reading "bATT", and no more numbers were shown. As I dialed the "battery" supply down, the measured voltage kept reading 10.00V until the battery was down to 5.3V.
As a contrast, I tried the same experiment with my Fluke 179. At 6.0V supply, the meter reads 10.56V, with the battery icon At 5.0V supply, the meter reads 12.43V, with the battery icon At 4.0V supply, the meter reads 15.13V, with the battery icon At 3.3V supply, the meter reads 17.73V, with the battery icon At 3.2V supply, the meter stops reading and the display goes blank. How close to perfect is the Cen-Tech? At 9.0V supply, the meter reads 10.09V At 8.0V supply, the meter reads 10.10V at 7.1V supply, the meter reads 10.11V At 7.0V supply, the meter reads 10.11V, but a rectangular icon that looks vaguely like a car battery shows up down in the corner of the display. What happens as the battery ages? I powered the meter with a separate, completely isolated adjustable supply instead of its 9V battery, and start dialing the supply voltage down to see what happens, while the meter is trying to measure the test voltage of 10.00V A perfect meter would consistently read 10.00V until it decided the battery was not sufficient, at which time it would stop reading. But my cheap meter is brand new with a brand new battery. That's good enough to do a lot of around-the-home diagnostics, even though it's not lab quality. Out of the box, the Cen-Tech reads 10.09V, or about 1% off.
Their calibration has expired, but they agree to the last digit, so I'm confident they're not too far out. But I wondered, is this thing OK for checking low energy voltages? I set my power supply to 10.00 Volts, as measured by my Fluke 179 and Fluke 16.
I had heard that Harbor Freight sells really cheap multimeters, and you get what you pay for, so I wondered just how bad could one be? To find out, I bought a $4.99 meter, item 92020, a Cen-Tech 7-Function digital multimeter with backlight, as described here I expected lousy build quality, lousy leads, and no input protection.
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