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  • TI Thinks Resolved

TIDM-1019: Calibration Table

Prodigy 225 points

Replies: 24

Views: 967

Part Number: TIDM-1019

Hi,

I've a problem with the adv. calibration Table, when enable, i don't have correct results. I'll explain all the steps i've done so far.

I've Flash my card with your default program (clean install), the only change in your code is the following one :

alg_results_float.volumeFlowRate *= 10.0;   //10x multiply

There is the result of our testing bench with adv. calibration table disable :

As you can see, the error is "correct" from Q4 (4741.19L/h) to 420.08L/h ( volume error of water going through the water meter).

Then I'm doing the calibration with USS (adv. calibration table disable) . I will use 3 ranges

Then, I disconnect the card, enable Adv. Calibration Table, generate headers, rebuild the program and flash the card.

I connect the card to USS, looking at the waveforms and check Adv. Calibration Table

Mean value stay at 0, it's perfect because no water is going through the water meter, but I've the following error :

1 ) I've an error 134 (The minimum volume flow rate falls outside the lowest alpha min calibration point), I guess it's linked to the second problem. How to fix this error ? By editing the "Flow minimum" of the first range ? Which value then ?

2) Volume on the card (LCD) stay at 0 and do not change when water is going through the water meter

I do a test at Q1 (26.361 L/h) with Adv. calibration Table disable, seems correct same result for the mean value when i was doing the calibration

Then i check Adv. calibration Table

Mean value is at 7.29 L/h and really far from Q1 (26.361 L/h), why ?

I've the same behavior for other flow rates

Best Regards,

Maxime

  • Hi Maxime,

    In order for this to work, you need to set the flow minimum(from the main calibration tab) to a negative value that handles the most negative value you will see.  

    I need to get back to you on the LCD issue and the strange results you are seeing after doing some more testing here.

    BR,
    Leo

  • In reply to Leonardo Estevez:

    Hi Leo,

    I connect the card with Adv. Calibration Table disable. I read the waveform of the flow rate (at 0L/h), after 5 minutes, min value is -0.75 L/h

    I set my minimum flow to -0.8 L/h

    Again, disconnect the card, enable Adv. Calibration Table, generate headers, rebuild, flash the card.

    Now, when i enable Adv. Calibration Table, no more error 134, and volume on LCD is working now.

    But always strange results :

    When Adv. Calibration Table is disabled, mean value = 0L/h  ==> OK

    When Adv. Calibration Table is enabled, mean value = -20 L/h ==> NOK

    I've also upload my headers as attached files.

    Regards,

    Maxime

    USS_Config.zip

  • In reply to Leonardo Estevez:

    Hi Leo,

    From what i see, i think the problem is with the Offset.

    For example :

    at 26.361 L/h -> mean value with Adv. Calibration Table disable = 31.4705 L/h

    For this range : slope = 0.908 ; Offset = -2.1241

    Expected value with the calibration table enable will be : (31.4705*0.908) - 2.1241 = 28.4384 L/h

    Value on USS : 7.29 L/h , I think there is a *10 on the offset

    (31.4705*0.908) - 10*2.1241 = 7.3342 L/h

    Same example at 0 L/h :

    at 0 L/h -> mean value with Adv. Calibration Table disable = -0.8L/h

    For this range : slope = 0.908 ; Offset = -2.1241

    Expected value with the calibration table enable will be : (-0.8*0.908) - 2.1241 = -2.85 L/h

    Value on USS : -21.87 L/h

    (-0.8*0.908) - 10*2.1241 = -21.9674 L/h

     

    Regards,

    Maxime

  • In reply to Leonardo Estevez:

    Hi Leo,

    I've done more tests.

    So, from my previous reply, it seems that the Offset is not correct (error of *10).

    I've changed the values directly in USS_meterVFRCalib.h and rebuild then flash the card.

    Good news, now mean flow rate on USS is the correct value.

    But I've a "constant" error on the volume from the LCD as you can see on my test.

    On our test bench, when we are doing the test for example on Q1, before the test start, we encode the initial volume (from the LCD), then the test will start, a calibrated piston will push a volume of water through the water meter at a constant flow rate, at the end of the test, we encode the final volume (from the LCD). Then the error is calculated (-6.42%).

    I'm pretty happy with the global curve on my screenshot. The easiest way to fix this problem will be to "lift up" all the curve by changing the Meter constant in USS.

    It will fix the problem of the error on the volume, but then the flow rate in USS and on the LCD will not be the right one.

    I hope these informations will help you to fix this problem.

    Regards,

    Maxime

  • In reply to Maxime Thomaere:

    Hi Maxime,

    Can you ensure you have averaging disabled for the results you are seeing on the LCD screen? Turning averaging off for the LCD is described in section 3.1.2.3.2 of the TIDM-1019 document.

    BR,
    Leo

  • In reply to Leonardo Estevez:

    Hi Leo,

    Can you provide the name of this document ? I was not able to find anything about "Turning averaging off"

    Regards,

    Maxime.

  • In reply to Maxime Thomaere:

    Hi Maxime,

    You can scroll through different modes on the LCD by pushing the buttons on the EVM. The up button turns the LCD on and if you push the right button 5 times this should put you into the non-averaging mode.(you need to wait until the message finishes scrolling on the LCD between each button press)

    Here is the link to the document:

    http://www.ti.com/lit/ug/tidudn0/tidudn0.pdf

    BR,
    Leo

  • In reply to Leonardo Estevez:

    Hi Leo,

    I don't understand how to disable the averaging. I guess the averaging is enabled because when i go through the menu the value is always changing.

    Regards,

    Maxime

  • In reply to Maxime Thomaere:

    Hi Maxime,

    You need to push the right button, wait until the text scrolls, push the button, wait until the text scrolls, etc. You'll see the text changes to describe what is being reported each time you push the button.  You should repeat the process of pushing the button and waiting for the text to scroll before pushing it again 5 times. The scrolling text should then say "Flow Rate in LPH".  In this mode, the individual flow rate measurement results are being reported.

    BR,
    Leo

  • In reply to Leonardo Estevez:

    Hi Leo,

    I think there is a misunderstanding. On the LCD, avg flow rate and Flow Rate in LPH are correct, I've done a test again with our calibrated piston at 42l/h, the mean value on USS match the value of the LCD and the value on our testing bench.

    But, to be able to calculate the error of the water meter, i need to use the volume. And the problem i encounter is with the volume from the LCD, not the flow rate.

    cc from my previous post :

    On our test bench, when we are doing the test for example on Q1, before the test start, we encode the initial volume (from the LCD), then the test will start, a calibrated piston will push a volume of water through the water meter at a constant flow rate, at the end of the test, we encode the final volume (from the LCD).

    ((Final volume (LCD) - Initial volume (LCD))  - (volume of our piston)) / (volume of our piston) = % error

    The easiest way to fix this problem will be to "lift up" all the curve by changing the Meter constant in USS.

    It will fix the problem of the error on the volume, but then the flow rate in USS and on the LCD will not be the right one.

    I think there is a problem with the volume on the LCD

    Regards,

    Maxime

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