Inputs with PH and ...
 
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Inputs with PH and EC (Issues)


bstent
(@bstent)
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I've got a Gravity EC meter (K 1.0 probe) plugged in through the gravity isolation board.

It's an analog system, so it's going via the ADS1115 board (currently EC is on channel 0 and PH is on CH 3) I have a PSI monitor running on CH1 which I have confirmed as accurate. At this point - I'm pretty sure the ADS is functioning correctly.

 

 

I'm unable to get sensible readings out of the EC and PH meters - I think this is because I don't understand the Mycodo inputs page for the sensors correctly.

My assumption was that the unscaled unit min and unscaled unit max were the minimum and maximum input voltages -which given that I have these powered off an independent regulated 5v supply (max 5A output) should be 0 and 5.

The output - according to the info here. says it should be 0 to 3.4V output.

 

 

I've tried a lot of different variations, but still can't get sensible readings... I don't actually know what I'm doing wrong, so have little to go on to correct issues I am facing. I'm using the bottled test solutions (1413 us/cm and 12.88ms/cm) - so would be expecting 1413.00 and 12800.00 readings - if 100% accurate - but I'm not getting anything like that at all.

One option I had that seemed to get close to viable answers was

Unscaled Min 0.0
Unscaled Max 776.82
Rescaled Min 0.0
Rescaled Max 5000000.0

Gain 16

This was trial and error - slowly working my way towards something that started to work - but I've no idea why these numbers are giving me values that are heading in the right direction instead of totally incorrect or almost totally fixed (previous attempts).
These readings show the 12.88 solution as 12754 (instead of 12880) - pretty close - and these readings change a little...
The 1413 solution is registering at 2654.

**Note** The solutions are 1413 us/cm and 12.88 ms/cm

However - this makes no sense to me and I need help to understand what data I should be looking at to solve this myself.

 

Anyone with some suggestions that I might try - and a little education as to how I work these things out for myself?

 

 

Thanks guys!!


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Kyle Gabriel
(@kylegabriel)
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Joined: 6 years ago
Posts: 570
 

If the output is 0 - 3.4 V, then this should be your unscaled min and max values. The unscaled range will be translated to the rescaled range. Have you verified the voltage output of your EC meter with a voltmeter? Have you verified the ADC is reporting the voltage being input to it?

Mycodo Developer


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bstent
(@bstent)
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I measured the voltage between the signal out on the isolation end of the board and the ground pin on the ADS - in the 12.88ms solution I get a steady 2.07v

On the 1413 us/cm solution I get 0.40V

 

How do I verify the ADC is reporting the voltage correctly?


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Kyle Gabriel
(@kylegabriel)
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Posted by: @bstent

How do I verify the ADC is reporting the voltage correctly?

Can you input a known voltage and see if Mycodo records that voltage?

Mycodo Developer


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bstent
(@bstent)
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I setup a new ADS1115 to look at all the raw inputs in Mycodo with these values 

If I remove all the input devices (CH0,CH1,CH2,CH3) the Mycodo says it is receiving 0.597V - Have I got some kind of voltage leak, or would this be considered normal operation? (See image Snip-ADS)

When I add the channels back in, I get 0.45V (fluctuates by 0.02V)

 

Measuring the voltage from the signal out (on the gravity isolation boards MCU end) to the ground on the ADS I get - 0.65V (device on CH1) and 1.36V (Device on CH3)

 

The ADS doesn't appear to be reporting the correct values, or something I have done in the Mycodo setup is messing them up.

Any suggestions?


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bstent
(@bstent)
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Added the image of the voltage reading I got with no devices attached to CH0, CH1, CH2, CH3


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bstent
(@bstent)
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Oh no - I think I've got a wiring issue...

I've looked at the voltages being shown by the Mycodo from the ADC - if the voltage rises on the channel I am using - the voltage also rises on the other channels - even ones I am NOT using, or are not even attached to devices!

i.e. if the voltage increases on CH0 (used for the EC meter), the other channels voltage readings rise too - this includes CH2 which is unused...

I'm now stuck with what to do.

 

This post was modified 2 weeks ago by bstent

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bstent
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Update:

I've measured the voltage coming from the sensor out on the devices attached to CH1

I get a 1.84 to 1.85V on the multimeter - which is consistent with this program running. (See console output in image)
This program is reading the data values and giving me the voltage on that particular channel every half a second - it correlates with the multimeter

The voltage that Mycodo is showing differs - and I don't understand why.

 

 

I'll take any suggestions at this point for what to try - this has been an issue for a few days that I simply can't work out myself :(


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bstent
(@bstent)
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Posted by: @kylegabriel
Posted by: @bstent

How do I verify the ADC is reporting the voltage correctly?

Can you input a known voltage and see if Mycodo records that voltage?

I've tried this - Mycodo is telling me that the voltages are different.

I've manually measured the voltage from the sensory to the ADC - then when it gets into the system software it appears as less than half of what it was. (See previous post screenshot - with the code console reading the voltages from the Pi itself)

All three channels on this ADS1115 are reading roughly the same voltage too - could this be a hardware compatibility issue (I've replaced the ADS unit already) 

 


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Kyle Gabriel
(@kylegabriel)
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I would not use a sensor's output voltage to test with. Sensors can be faulty or output a fast changing voltage that's not perceptible to a multimeter but will manifest as variable measurements on an ADC that measures an instantaneous voltage. I would connect a AA battery, a benchtop regulated power supply, or similar that you know there is constant voltage.

Mycodo Developer


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bstent
(@bstent)
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Will try with a couple of different fresh batteries and see what I get.

I ended up installing it to the outside patio over the weekend after sacrificing the water sensing parts :(, so nice to think I'll be able to get that up and running for the summer.

 

Will let you know in a day or two when I get to play with it again :)

Thanks!


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