That big orange mallet is the secret to success.For now, here's the motor I designed, almost assembled enough to test next week.
View attachment 99020
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That big orange mallet is the secret to success.For now, here's the motor I designed, almost assembled enough to test next week.
View attachment 99020
Well then why not filter the PWM at the source where you got plenty of space so that it is not a noisy square wave but rather a nice DC at the correct voltage/current?Yeah I know, and that would solve some other problems too, but unfortunately that's not an option; PWM comes from topside and it must stay that way. The whole point of this exercise is to shrink the subsea electronics capsule down from the size of a duffel bag to the size of a cigar box. and what you're suggesting would increase the capsule size to that of a shower stall.
I guess because it is an induction motor, and induction motors do not work well at DC.why not filter the PWM at the source where you got plenty of space so that it is not a noisy square wave but rather a nice DC at the correct voltage/current?
I'll draw it up and post it as soon as I figure that out. Right now it exists only as a disarray of random componentsWhat type of circuit did you use?
https://www.bb-elec.com/Learning-Ce...op/Current-Loop-Application-Note/curentlp.pdf
It is filtered, coming out of the VFD; goes through a sine filter. It goes in looking like raw garbage and comes out looking like grilled garbage.Well then why not filter the PWM at the source where you got plenty of space so that it is not a noisy square wave but rather a nice DC at the correct voltage/current?
do you have access to a spectrum analyser, or a scope with an FFT function so that you can see the noise in the frequency domain and compare with the spectrum of the wanted signal.
Then you could decide if filtering was appropriate.
I did the two small plates on the black gearbox. Boss man made me farm the rest of it out.Wow, that is awesome, did you do the machine work yourself?
Hy strantor,
I think you would have a much more noise immune and reliable comms link by adopting one of the Analog Devices approaches described in post 29, preferably RS485.
I realize that I haven't fully exhausted RS485 as a viable option. There are better products than what I'm using, that stand a better chance of working. But per what I've seen on my oscilloscope, the outlook for any voltage-based comms (differential or otherwise) appear bleak. The digital current loop interface I'm experimenting with seems much more reliable to me in concept, and in observation.I strongly agree with spec; the circuit you posted isn't going to have very good noise rejection, and you'd be much, MUCH better off going with one of the chips he listed.
http://cds.linear.com/docs/en/datasheet/2881fi.pdfAnd an isolated RS485 module (with isolation PSUs): http://cds.linear.com/docs/en/datasheet/2881fi.pdf
Can you not see it? I entered it years ago and it still shows on my screen -(would you consider putting your location in your displayed ID)
I realize that I haven't fully exhausted RS485 as a viable option. There are better products than what I'm using, that stand a better chance of working. But per what I've seen on my oscilloscope, the outlook for any voltage-based comms (differential or otherwise) appear bleak. The digital current loop interface I'm experimenting with seems much more reliable to me in concept, and in observation.
It would be cool if this wasn't BGA. I wouldn't know what to do with that.
Can you not see it? I entered it years ago and it still shows on my screen -
View attachment 99061
A new brain would help too.I can see the location. I suspect that spec needs new specs
Observation #1 - I did see extraneous bits come in while I wasn't transmitting. I was running a program which would transmit 20bytes of data once per second. In between transmissions, a string of random data would print out. During the transmissions, sometimes characters would be wrong; I suspect it was noise coming into play with every logic LOW, changing random bits from 0s to 1s. I suspect this is the result of having a passive low state. In the low state, there was no current to oppose the noise current, therefore crosstalk occurred. I corrected this by changing my current drive output to an h-bridge. Now I'm driving an active low (negative) and I get no more extraneous bits or modified bits.
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They're just too slow. I'm going to upgrade the optos and see how fast I can push this circuit, despite the fact that 19.2kbs is already double what I defined as my minimum baud rate.
Yeah I drew the circuit exactly as I had it set up on breadboard. Using the same p/s for both ends. I since separated the circuits and they both run on their own isolated supplies now. I did not notice any difference in doing that.If I understand the post #30 schematic correctly, the two ends that are 200 m apart still will have common +12 V and return connections with or without galvanically isolated data comm parts in post #29 and after. That is, the transmitter and receiver will be common powered, common grounded, and 200 m apart. As long as the +12 V and its return are galvanically isolated from all of the high voltage goop, I don't see any advantage to yet another isolation barrier. It can't decrease the capacitive or inductive coupling from the aggressor lines, and the receiver optocoupler's LED is a defacto differential receiver that rejects common mode modulation. In fact, depending on how the interference propagates, you might be able to eliminate the optocoupler on the left and replace it with a small darlington. I used a very similar arrangement to get data into a TEMPEST isolation area in a crypto system. Eliminated an entire fiber optic link thought mandatory to meet a 130 dB isolation requirement.
Also, since speed isn't an issue and noise coupling is, selecting a less sensitive optocoupler should increase your noise immunity. The 4731 takes only 40 uA to wake up, while a 4N35 et al takes about 50 times more current. The 270 ohm resistor does a lot to desensitize things, but the right side opto sees an impedance 5 times greater. I don't think it would hurt if it were a little more deaf. Inducing 40 uA through 1.5K takes only 60 mV of noise.
ak