I've never seen a Radio Shack meter before - I have no idea what that meter is measuring or what it's set to. It could be set to read micro volts, but it would be odd for them to take a close-up photo if it was reading a tiny number. But then maybe that's why they went with an analogue meter - big needle swing is psychologically persuasive.
So it is. I tried to find a big picture of that multimeter to see what it was set to because the video image quality it poor, but now on closer inspection I can see it's set to AC volts. The most similar analog radio shack model I could find a picture of extended the resistance area further up the dial.
Yep, it's a narrow-range (~2 ohms) precision ohm meter, specifically a Wheatstone bridge[0]. Newer models have a microcontroller. There is a teardown video[1] of a newer model found on eBay. Scientologists spared no expense (e.g. $20 potentiometers, custom injection molded case)!
There's also an older teardown and a huge amount of info from Dave Touretzky on these things [3]
Ye olde ammeters were secretly voltmeters with a low-value but high-precision shunt resistor in series with the circuit to be measured.
Current passing through the resistor causes a tiny voltage drop, which is measured by the meter. As the voltage is proportional to the current, the scale painted on the cardboard behind the needle did the actual conversion.
In the author's setup the fuse takes the shunt's place; its resistance is apparently a known value that can be gathered from a datasheet.
> I hooked the ground crocodile clamp of my scope to what I thought was the ground but which in fact was V- of the DC supply voltage of the neon light installation that was use to drive the display.
Yeao! I own a couple of high-voltage differential probes for this very purpose. Even though most single-ended scope probes are rated to 300V Cat II, I won't go anywhere near main's power with them.
According to the article, it was monitoring bus voltage, but I could imagine it was used to measure the current being used by the telemetry system. So if it was used as an ammeter, it would've been placed in series.
Is there no scope or meter part? Playing around with the examples it's visually impressive but is there a way to probe say the voltage at a particular wire?
A lot of older multimeters look like this: http://www.eevblog.com/forum/chat/show-your-multimeter!/540/ or something similar at least once handheld meters with multiple modes started to become an actual item. That whole thread is a decent cross section of multimeters, though it's skewed towards nice older meters as opposed to lower grade meters.
The best touch in that story is how the poster works around the lack of a voltmeter by assuming the OP possesses a soldering iron and the skills to use it.
Bought originally by my father, most likely when he was on contract in Kuwait in the 80s. It fell out of use as he stopped doing any sort of electrical work citing typical age-related issues.
The battery cover is gone and the plastic body feels kind of loose, but otherwise it's fully functional(even if de-calibrated). The original fuse is still there, but I wouldn't use it for any high-voltage applications.
I was helping a friend repair some old (WW2 vintage) transmitting gear. The voltage dividers used to bias the tubes used almost 100 watts by themselves! Quite the contrast to modern electronics.
I've never seen a Radio Shack meter before - I have no idea what that meter is measuring or what it's set to. It could be set to read micro volts, but it would be odd for them to take a close-up photo if it was reading a tiny number. But then maybe that's why they went with an analogue meter - big needle swing is psychologically persuasive.
And Dweck is no longer involved - http://www.businessinsider.com/college-roommates-founded-hot...
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