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Thread: KHD not working properly - What to do?

  1. #1
    Join Date
    05.12.2019
    Posts
    6

    Default KHD not working properly - What to do?

    Trying to setup a brand new KHD with doser 2.1 SA and connect to a Profilux 4. Everything is connected and setup as instructed in manual, doser set as slave of course, and setup mechanically. Khd/doser performs test - but values are to low according to ref solution.

    With ref solution (7,5 dkh) I get 5.8-5.9 - the value is constant - I've used almost 1000 ml to perform multiple test in a row and cant figure out why it wont give me correct value.

    So far..

    Probe - calibrated several times.

    Water sample hose - I have different diameters on some of the tubes so I filled the entire hose incl pipes, filter, doser hose etc and measured the volym. This is the volym I've entered into GCC when registering "sample tube volym" - it's 46 ml.

    Doserheads are all calibrated several times.

    Cleaned rolls on doser pump 3 since it made alot of noise and got stuck. Based on my observations it works fine now.

    Sample volum is set to 100 ml.

    What else could I try to get more accurate test results?

    When measuring aquarium water the margin is 0,9-1,1 – For example KHD sats 7,7 when all other tests says 8,6-8,8

    How is this possible?

    Tests are done after fresh calibration session and the only thing in between is emptying cell and flushing cell with «new» liquid (the same that are going to be tested).

    I assumed margin of error would be bigger with aquarium water than ref soution since it could bring some problems as micro bubbles etc could «polute» the test water.

    / Andre.

  2. #2
    Join Date
    05.12.2019
    Posts
    6

    Default

    Adding info.

    When calculating the entire sample hose volum I get 46 ml - this is done by filling the entire line and dosing it into a measuring cup.

    When the line is emtpy I type in 46 ml into manual dose at set speed and click go but the entire line doesnt get filled with water.

    First I thought this was due to bad calibration so I re-calibrated again and again and again but I still get the same number. 36 ml/min.

    Would placement of doser, khd and water intake have an impact on this? Shouldnt the doser - correct calibrated - calculated the necessary run time and fill the line with exactly 46 ml?

    My nest step is to measure what the doser actual dose when trying to dose 46 ml and perhaps add the difference or try to cut the hose some more.

    Grateful for any help.

  3. #3
    Join Date
    30.06.2018
    Posts
    48

    Default

    Quote Originally Posted by Dimorb View Post
    Adding info.


    When the line is emtpy I type in 46 ml into manual dose at set speed and click go but the entire line doesnt get filled with water.


    Grateful for any help.
    I'd suggest manually dosing 47ml and see if that fills the line. If not try 48ml and keep woking your way up until it is filled.

    What are you using to calibrate your dosing heads?

  4. #4
    Join Date
    05.12.2019
    Posts
    6

    Default

    Yes that would be the next step.

    But it's really weird that the volume in the tube are 46 and the doser doesnt fill it entirely even when calibration are the same.

    I use a graduated test tube from laboratory.

    Also.. previously - I've shortened it down now - I used a really long hose between aquarium and the unit and noticed it's not possible to set water sample hose volume bigger than 50 ml. Is there a work around for this? If so I could try to add the "missing" ml's and see what happens to the measured value.

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