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Thread: Coffee machine experiments
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16th Sep 2019, 11:54 PM #61Most Valued Member
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17th Sep 2019, 12:19 AM #62Member: Blue and white apron brigade
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17th Sep 2019, 01:27 AM #63
Hi Michael, Bob, Guys,
My only concern about using shielded cable for the VFD output is obtaining a cable with sufficient voltage rated insulation along with the current carrying capability you need.
Also the connectors for shielded multicore cable are expensive and not that easy to obtain.Best Regards:
Baron J.
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17th Sep 2019, 06:54 AM #64Member: Blue and white apron brigade
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One of the most useful things I picked up when scavenging stuff from the hospital demolition site was a roll of 6 core shielded cable. I think the cores are 1mm which is more than enough for the 1/2A total current draw by this small (1/5 HP) motor and the insulation tests better than 100MΩ so it should be fine for 240V.
Connector wise, the Arduino enclosure is plastic so even though I have some fully metal enclosed connectors/feedthroughs they are not going to do much.
Now I need to get that roll of 6 core wire back from Anorak Bob!
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17th Sep 2019, 01:18 PM #65Senior Member
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You could also consider differential mode adc - eg ADS1115.
This should help with sensors like the thermocouple and flow.
Russ
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17th Sep 2019, 08:06 PM #66Member: Blue and white apron brigade
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17th Sep 2019, 09:08 PM #67
Hi Bob,
Try adding a couple of turns through the ferrite ring, and if you now have shielded cable only earth or ground the cable at the VFD end.
Ferrite beads are useful on individual wires close to the ends of ones carrying signals.
Good luck ! I've spent many happy hours chasing RF leakage down only to find that its coming from the most unexpected place.Best Regards:
Baron J.
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17th Sep 2019, 11:19 PM #68Member: Blue and white apron brigade
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That is whatI have done.
Ferrite beads are useful on individual wires close to the ends of ones carrying signals.
Good luck ! I've spent many happy hours chasing RF leakage down only to find that its coming from the most unexpected place.
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18th Sep 2019, 09:26 AM #69Member: Blue and white apron brigade
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I found another issue contributing to the noisy TC problem.
So that I don't have to turn on 3 mains switches (coffee machine, VFD/Motor, Micro-controller[MC]) just to have a coffee, I wired the mains for the VFD/Motor and the MC via the coffee machine. This meant the coffee machine mains switch powers up all 3 system components. However this means the earths for the VFD/Motor and MC are all going through the Coffee machine.
When I run these direct from the same GPO as the coffee machine (ie NOT through the coffee machine) there is a further small reduction in TC noise.
So although its more work I will connect the VFD/Motor and MC direct to the mains, but switched via a relay powered via the coffee machine.
Yeah I know - what a load of palaver.
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19th Sep 2019, 06:49 PM #70Member: Blue and white apron brigade
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Set up the mains power supply to the VFD and Microcontroller (MC) so they are powered from the same outlet as the coffee machine
Remember I want to turn on the VFD / MC and coffee machine from the one switch.
Outlets
The 5 way GPO.
1: Electric kettle power
2: Ginder 1 power
3: Coffee machine power
4: Grinder 2 power
5: Power redirect to double GPO above the 5 way outlet.
R: Relay - Switched by coffee machine power - Connects power from outlet 5 to the double GPO above.
6: VFD power
7: MC power
Messy cables I know!
Powerdistr.JPG
Getting closer
Display1.JPG
With regards the thermocouple noise I tried a couple of other things.
I tried shielding the TC cable between the machine and MC with shielding grounded to Earth - Didn't do much.
Tried locating a "snap on ferrite" just on the TC signal line, and then just on the ground, no good - have to wrap both ground and signal line around the ferrite core.
I want to wind more of the TC lead around the "snap on ferrite" but the TC lead is not long enough so will be making a new one.
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19th Sep 2019, 07:21 PM #71
Hi Bob,
You have to determine which of the items is creating the hash, then the ferrite filter bead needs to be as close to the source of interference as possible. With those multitude of wires the interference can wonder from wire to wire at will and will also vary as the wires are moved around, particularly when coiled up together.
One source of interference that you may have overlooked is the Ardino itself. The clock can radiate a modulated signal that will escape down any wire and interfere with its self.
One piece of equipment that I used to use was a small insulated two turn loop diode probe and an oscilloscope set on its most sensitive range. You could get away with a high impedance multimeter but you would have to make the probe as an adaptor to get rid of the meter leads. At one time I had an op amp in a die cast box to amplify the diode output to a 25 ua meter. That worked quite well when I made it into a variable tuned one.
Interference is a most difficult thing to pin down, nowadays manufactures spend thousands to make sure that their equipment meets interference standards.Best Regards:
Baron J.
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19th Sep 2019, 08:11 PM #72Member: Blue and white apron brigade
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Yes it is a bit of a dog's breakfast so it does not surprise me there are probs.
One source of interference that you may have overlooked is the Ardino itself. The clock can radiate a modulated signal that will escape down any wire and interfere with its self.
It's definitely the VFD generating the noise as only when I turn on the VFD (not even motor running) do things go pear shaped, when the motor runs things get slightly worse.
One piece of equipment that I used to use was a small insulated two turn loop diode probe and an oscilloscope set on its most sensitive range. You could get away with a high impedance multimeter but you would have to make the probe as an adaptor to get rid of the meter leads. At one time I had an op amp in a die cast box to amplify the diode output to a 25 ua meter. That worked quite well when I made it into a variable tuned one. Interference is a most difficult thing to pin down, nowadays manufactures spend thousands to make sure that their equipment meets interference standards.
All during today I've been comparing the Arduino temps with two other battery powered TCs. On the bench away from the machine/VFD they agree to with a degree but due to working positions problems in situ comparisons are difficult as the working position of the Arduino TC is deep inside the machine and I cannot locate the other two TCs in the same location at the same time. I can get one of the battery powered TCs within about 15 mm of the Arduino but that's about it - the other one is about 30mm away.
After waiting for the machine temp to stabilise (tricky because the boiler thermostat is either on or off ie either heating or cooling) I can then turn the VFD on/off (takes about 15 seconds to stabilise between switching) and compare the temps. The latest round of testing suggests the temps now agree most of the time to within less than one degree.
Screen Shot 2019-09-19 at 6.30.16 pm.png
However I cannot compare the displayed temps with and without the VFD while running the pump as the VFD is needed to run the pump. Also while the pump is running the water temp change significantly as the pump flushes out overheated water that has been sitting in the heat exchanger and replaces it with fresh cool water. To do this I need to compare temp profiles with the old pump but I will be blowed if I'm reinstalling it.
Despite all this I feel I'm getting closer - how close is enough is yet to be determined
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20th Sep 2019, 01:13 AM #73
Hi Bob,
OK, based on what you have told me, you are sure that its the VFD, can you put the VFD into a tin box with a ferrite ring on both the inside and outside on the output wiring and put a ferrite ring on the mains input lead on the inside as close to the tin box wall as you can get it. That should Knock anything coming from the VFD out completely.
It should kill anything going back up the mains lead and anything coming down the output leads. The tin box will stop any radiated interference getting out.
You should now have a quiet system.
HTH.Best Regards:
Baron J.
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20th Sep 2019, 09:05 AM #74Member: Blue and white apron brigade
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20th Sep 2019, 12:25 PM #75Member: Blue and white apron brigade
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Said cake tin turns out not to be quite large enough bit according to SWMBO her Mum's place (40km away) has a stash of square cake tins that are about to be thrown out.
To test the effect of enclosing the VFD I wrapped it in Al foil.
Not a very good job of wrapping but it looks like it makes a significant difference.
The first thing one notices is the transient changes in the temperatures are much larger and longer when switching the VFD ON/OFF.
Immediately following switching the VFD On/Off the temp jumps by as much as 2º then settles back down over about 10s .
The temperature difference between on an off are now down to about 0.3º which is about the same as the second to second variation in readings anyway.
Anyway I have seen enough to warrant pursuing an enclosure.
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