I just got a Rigol DS1052e scope and a Rigol DG1022 arb gen.
To test them, I built a full wave rectifier using 1N4000 series diodes and a 500ohm resistor for load.
I set up the arb gen for a 60Hz sine wave, 5 volts peak to peak, no DC offset and connected it to the red and yellow cables
The green and blue cables go to the resistor. I hooked the probe on the resistor terminals and the result on the oscilloscope was that of a half wave rectifier
I tried increasing and decreasing the voltage and frequency but still nothing. I used another set of diodes, in case one of them was bad, but still the same output.
I connected the probe directly on the arb gen output and I got a nice sine wave.
What is causing my full wave rectifier to behave like a half wave rectifier?
I’m on a computer where I can’t see any of your images; I’ll check them when I get home. But here are a couple things to think about:
Your output voltage will always be around 1.4 V less than your input voltage.
Is your function generator output and your scope input *both *referenced to ground? If so, then you may be shorting out one of the diodes in your full-wave bridge rectifier. One of them - either your function generator output *or *your scope input - can’t be referenced to ground. If this is your problem, the easiest solution is to connect Scope Ch. 1 to one side of the resistor, Scope Ch. 2 to the other side of the resistor, and then have your scope calculate the difference (Ch. 1 minus Ch. 2). Or you can use a differential probe (expensive). Or you can float the scope (only do this if you know what you’re doing).
One side of the scope input is grounded. One side of the function generator output is grounded.
Unless either the scope has a floating input, or the generator has a floating output, it can’t work without some changes. Google isolation transformer.
This was a problem with old cheap TV sets and radios. They rectified the line, which means to work, the chassis had to be floating…otherwise known as “hot chassis”. Clipping your scope ground lead to that chassis resulted in sparks and damage to your TV or your scope, and sometimes both. This once caused SWMBO to decide I wasn’t an electrical god after all. Just as well, I hated when she’d slip up and call me Odin during sex.
This is most likely to be the cause; you can also get the same results if one of the diodes is shorted or open, although that probably isn’t likely unless you were using them in some high current/voltage power supply (solderless breadboards are also notoriously unreliable; well, at least in my experience, but they aren’t supposed to be used for high-power, especially mains powered, circuits, mainly because the plastic/contacts melt).
This is still true for modern electronics as well (not necessarily cheap either, the majority of pre-SMPS non-vacuum tube TVs used direct line connection to avoid using a big isolation transformer), at least for the primary side of the power supply (switchmode power supply, which are ubiquitous now); as mentioned earlier, the easiest solution is to remove the ground prong on the oscilloscope power cord (yes, I know that isn’t safe, but then I don’t want to shell out $$$ for a big 500-1000 W isolation transformer, and not as dangerous as some of the older things I made - built on a completely exposed metal chassis which is live :eek:).
Well, theoretically you don’t need to connect them to anything, because the scope ground and function generator ground are already tied together via their power cords at your 120 VAC outlet. But while doing this looks O.K. on paper, you don’t want to make a habit of relying on the power cords for connecting earth grounds, since it forms a big loop and is thus susceptible to all kinds of induced noise (primarily magnetic fields). So it’s best to connect each alligator clip to the ground on the output of the function generator (i.e. to the “outside” of the generator’s BNC connector), which is also connected to two diodes in your bridge rectifier.
I’ve floated a scope many times using a “cheater” adapter on the AC plug to lift the ground. I never recommend it to others, however, since I don’t want to be responsible for getting someone electrocuted. I remember donning rubber gloves once to make sure my scope didn’t zap me.
Here in our lab at work we recently invested in some differential probes for our scopes. They’re not cheap, but gosh are they handy. We also purchased a battery-operated scope that has an EN 61010-1 rating.
I am not afraid of floating the scope, I used to live in an old house that had ground wiring only for the water heater and electric oven, the sockets were not grounded. So essentially all my devices were “floating”
Y’all made up everything in this thread, and you’re not actually talking about anything at all, right? This is one of those gag threads. I get it. I read every word, and I don’t even know what FIELD you’re in. I didn’t look at the videos, because i was afraid it might spoil the mystery. love that about the SDMB.
I “floated” the scope and it didn’t help! Still same output.
I hooked Channel 1 on the input and see a sine wave. But when I connect channel 2 across the resistor, the bottom part of the input sinewave gets cut out and input and output basically becomes the same
The only way to get a correct reading was using the differential method mentioned by Crafter_Man
Should I float the generator too? I had only one float cable. ThelmaLou, this is Electronics 000 (not even 101).
I set up the desired peak to peak voltage and freq on the generator.
I put a bnc T-connector on the generator output and connected one 50ohm coax cable (was supplied with the generator) to Channel 2 of the scope and another cable (with crocodile clips on the end, custom made) to the input of the circuit. I terminated the unused port on the T-connector with a 50ohm terminator.
I did that because I wanted to see both input and output, but I guess this setup messed up the grounds.
I remember donning rubber gloves once to make sure my scope didn’t zap me.
