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  1. #16
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    Have you considered using a DS18B20 digital temperature sensor rather than a thermocouple? They are easy to use with arduino and likely to work well in a noisy environment.


    Sent from my iPhone using Tapatalk

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  3. #17
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    Thanks for the lead. I'm no longer using the thermocouples but am trying to use the DHT22 only because I already have some on hand. The DS18B20s sound good and seeing as they only cost a few $ I will give them a go.

    Do you know the names of the drivers etc that are used in the Arduino programming?
    Cheers

  4. #18
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    i think it's the "wire" library (for one-wire)

  5. #19
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    While waiting for the new temperature sensors to arrive I though I would finish up the DC pressure side of this meter/measuring system.

    To reduce the number of times I have to connect and disconnect poly tubing to the meter when testing different t things I set up a couple of aquarium air manifolds as shown below.

    The 2 way manifold labelled +veP (positive pressure) is connected to the positive pressure side of the sensor (A). This is used to measure +ve pressure which is on the outlet side of an impeller - below I will describe a couple of uses for this. One tap is for a measuring tube (currently its connected to the inside of the enclosure), the other "not connected" tap is for zero or atmospheric measurements

    The 4 way manifold is for negative pressure measurements and connects B on the manifold to to the negative pressure side of the sensor (B) and is for pressure measurements before the impeller. Most measurements will be of this type. One of the black poly tubes is connected to the ducting immediately above the impeller and the other is not yet connected to anything. One of the unoccupied taps is for zero (atmospheric measurements) and the other will be used for a floating measurement ie a long length of tubing able to be connected to various places in the ducting.

    The reason I need separate +ve and negative manifolds is because the sensor will not measure negative pressure much below zero. I could of course swap tubes around but I want to avoid do thing ie just turn little taps.

    Manifolds.jpg

    The first thing I thought I would check is the back pressure produced by the DC enclosure.

    I have always felt some resistance when I close the last of the 3 doors on the enclosure and have always wondered how much resistance it was causing.

    This is a positive pressure measurement so uses a tube on Manifold A relative to a tap at atmosphere on manifold B.

    Before a measurement is made a zero or reference point is needed.

    Now things get tricky. This thing is so sensitive that "zero" inside the shed is slightly different to zero measured outside the shed, and changing the length of the tubing and where zero is measured changes the zero. What matters is the zero as measured using the same length of plastic tube that is used to measure the final pressure. So I have one reference point as one of the open taps on manifold B , and the other point is at the end of the tube inside the enclosure, but now instead of being inside the enclosure I temporarily move it outside the enclosure - this is the black tube on manifold A, and generates the green pressure data lines below. Things are even trickier than I state because slight changes in the speed and directions of breezes around the shed screw around with the pressure readings so we have to bracket the measurements.

    The green line shows a starting working zero of about 60 Pa but at the end of the experiment when I repeat this Zero measurement the average zero pressure has risen to ~65Pa.



    Enclosuretests.jpg

    Now I move the black tube that was outside the enclosure inside the enclosure but leave the enclosure door open and start the DC. This generates the blue line data and the pressure appears to go up slightly compared to green line and statistically I can just see a difference. If I collected more data it might become clearer.

    Then with the DC still running I now close the enclosure door and this generates the red line data ~80Pa. Here there is a clear difference in positive pressure compared to the blue and the green lines. This tells me my escape path (S shaped baffled pathway) for the air out of the enclosure is constricting the air flow. The pressure difference averages about 14Pa which is about 0.06" or 1.4 mm of WC. So while it feels like a lot of back pressure when I go to close the enclosure door it's actually less than 1% of the total static pressure at 50Hz.

    There is even a teeny weeny statistical difference between the blue (P measured inside the enclosure with door open) and the green (P measured outside the enclosure) data.
    The effect is very small, ~ 3.5 Pa ( 0.015" or 0.035mm of WC) remember this is with the doorway is wide open. This is useful because it tells me I would have to open up the air escape path a long way to gain much of a benefit. In other words live with the escape path I have got.

    These were quick and dirty measurements - I'm sure if I chose a still morning and collected more data I could get a clearer result. I am really pleased how the pressure sensors working.

    So many measurements to make - so little time.

  6. #20
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    Quote Originally Posted by arniew View Post
    Have you considered using a DS18B20 digital temperature sensor rather than a thermocouple? They are easy to use with arduino and likely to work well in a noisy environment.
    I ordered a set of 3 DS18B20s - dirt cheap and they are indeed very easy to use but they also don't like the electrical noise. I am now investigating shielded cabe but I fear I may have to replace the 3Phase cable that goes between the VFD and the Motor with a shielded cable. This is the first time I have had these problems although in this case the cable between the VFD and the Motor is much longer than usual (3m versus 500 or so mm, in most of my other cases)

  7. #21
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    Sorry to hear about your issues. I have done some micro controller based designs in Industrial applications. Managed to solve noise issues in very noisy environments. However i rather designed a board that was noise "resistant". I found my biggest source of noise was actually coming through the power supply....caused by the VFD and solenoids and contactors switching

  8. #22
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    Quote Originally Posted by ericks2 View Post
    Sorry to hear about your issues. I have done some micro controller based designs in Industrial applications. Managed to solve noise issues in very noisy environments. However i rather designed a board that was noise "resistant". I found my biggest source of noise was actually coming through the power supply....caused by the VFD and solenoids and contactors switching
    Guess what!!!!!

    I've been mucking around with this thing for most of the day.
    Inside shed - outside shed- inside enclosure, outside enclosure - on my electronics bench
    With VFD on/off, with motor on/of
    Running the PS for the Arduino from a completely different circuit (I have two feed lines to my shed).
    Shielded cable - non shielded cable, earthed and not earthed, earthed at one both ends etc
    ETC
    Very disconcerting because nothing was that reproducible.

    Then I came in a read your post and remembered I had a similar problem at the mens shed which I solved by using a battery.
    SO I tried the battery and it's much better but not completely solved as it still sometimes drops out (shows -127ºC) but only for one or the other of the two sensors.
    It does not drop out for long (maybe 2 -5 seconds) and then comes back on line. then 5-10 mins later it does the same thing but usually ttheeh other sensor drops out - I think something is switching on/off somewhere doing this.
    It's almost good enough to live with it but I have far from optimised the shielding so tomorrow I will be doing that.

    So the plan tomorrow is to try out a bunch of PS and see which is best and if that fails to use battery in the short term while I look for a build a better PS.

  9. #23
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    I am glad you making progress....in my case i made my pic micro based "plc" to work off 24V dc. I used a combination of filter components and opto isolated devices to make it work in the noise. Initially the micro would reset or the lcd would show garbage. Have to admit it took me 85+ hours of work/experimenting to solve these issues. I am no expert but i do have a lot of patience with this sort of stuff

  10. #24
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    Quote Originally Posted by ericks2 View Post
    I am glad you making progress....in my case i made my pic micro based "plc" to work off 24V dc. I used a combination of filter components and opto isolated devices to make it work in the noise. Initially the micro would reset or the lcd would show garbage. Have to admit it took me 85+ hours of work/experimenting to solve these issues. I am no expert but i do have a lot of patience with this sort of stuff
    That's what the one at the mens shed was doing.

  11. #25
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    I had a look into low noise filters and then I looked on the web to see to see what was available as premade modules.

    One newish gizmo I came across was an up to 36V, 1A, 4.2µVRMS, RF low drop out Voltage regulator chip by Texas instruments called a TPS7A4700, and small modules with this chip on it are available for about $13 delivered. These devices appear to have some of the lowest noise filtration available and are highly rated by the hifi community. As the majority of my projects are under 1A this type of thing might work for me so have ordered one to have a play with.

  12. #26
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    Buying a ready make unit is great......wish i had found something at that time

  13. #27
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    Have been trying to systematically narrow down the problem.
    This morning I tried out 4 different 12V DC adapters (DCA), 4 different USB adapters, and a PC PS, two different batteries and a bunch of different cables.
    By sensors I mean Temperature Sensors.

    Using a battery with a 1m USB cable results in ~20% sensor failures compared to near 0% failures when using a short (200mmm) USB cable.

    DACs - all have 1m+ long unshielded leads
    The sensors fail 100% of the time when using one of the DCAs even when the DC or VFD are off. ie micro controller running and works, but temps reported are nonsense - it also has he longest lead between the adapter and the MC.
    When using the PC PS, and 3 of the 4 DACs the sensors fail as soon as the VFD is switched on, and then also when the motor is running.

    With the USB adapters all used with a 1m long USB cable between USB adapter and MC.
    When using 1 of 4 USB adapters the sensors fail ~ 50% of the time, even when the VFD is off, 80% of the time with VFD on, and 100% then with the motor running.
    With 2 of the 4 USB adapters the sensors work fine when the VFD is switched on, but as soon as the motor starts the sensors fail
    The fourth USB adapter works fine up to when the motor is running where the sensors fail ~50% of the time - I call this the "best" USB adapter.

    Connecting either battery to a charger - sensors fail as soon as motor is turned on.

    After all that there seems to be a correlation in failure rate with the length, shielding and orientation of the cable between the PS/adapter and the micro controller.

    USB cables are better - they should be, they're shielded.

    Using the "best" USB adapter with a short (200mm) USB cable results in about a 20% failure rate with the motor running. This is getting close - I will try an even shorter USB cable.

  14. #28
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    It would be nice if you could post some pics of the setup

  15. #29
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    Quote Originally Posted by ericks2 View Post
    It would be nice if you could post some pics of the setup
    There's not much more to show than what's in the picture in post #19.

    I was at Altronics on Saturday and bought a $10 in-line EMI filter for mains power and used that to power the adapters. It reduced the numbers of sensor fail reads when powering the MC with the better USB adapter but it did not improved the success rate of the sensors when using other Power Supplies.

    The ebay supplier of the low noise TPS7A4700 module contacted me saying that due to high demand they are having trouble with supplying these modules and it could take another month or two before I can get it. In the meantime I will just run from a battery. The MC on draws 35mA to function so it will run for many days on a single battery charge.

  16. #30
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    No worries...thanks. Like i said i made a 24V/5V filtered converter/psu for my noise issues. The main component and crucial one was a common mode choke, similar to this one

    choke2.jpg

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