KHD not working properly - what to try?

[Dimorb]

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.

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

Sample volum is set to 100 ml.

/Andre.

 

[Dimorb]

I cant get my mind right about this..

I reset everything - new calibrations, shortened the hose, changed data in GCC, empty cell, flushed cell etc.. and retried again with aquarium water - this time it measures 1,5 dkh.

Anyone have any ideas?

I've talked to GHL and I could send it in to get it checked but if there's nothing wrong I'll have to pay and it seems unnecessary if there's something I could do on my own.

Earlier pump 3 stopped in the middle of every test - sounded awful - and the test was stopped but I loosened the caps and cleaned the rolls and after that everything sounds good and it looks like all the pumps are working as they are supposed to.

 

[Dimorb]

Adding more info..

I've used almost 1000 ml ref solution and almost every test comes back around 5,8-5,9 when the text on the bottle says it should be 7,5 - this is a negative margin of 1,6-1,7 dkh.

when measuring aquarium water the margin is 0,9-1,1 - KHD for example says 7.7 when all other tests says 8,6-8,8

How is this possible?

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

 

[GalaxyBenny]

So I just setup my own KHD 2 days ago, so I am by NO means an expert. But I have a couple of "silly" things probably for you to check. I know they will sound obvious, but since you didn't mentioned them specifically I'd say it's worth a look.

1) How long is your line from the KH Reagent to the doser? I believe the instructions say something like 27" maximum.

2) Did you triple confirm that the KH Reagent lines are totally bubble free? I know in my own case I had an air bubble AFTER the doser (between the doser and the KHD). I had to take the line off and flick it several times to get the bubble out.

3) With your probe, after you calibrate it did you confirm the actual value in the controller? In the KHD screen itself, near the bottom you can see the current value of the probe. After calibration I put my probe in each reference solution for 4-5 minutes to make sure it read within +/- 0.1 pH of the solution. Just to double check it was working correctly.

4) Just to double confirm, AFTER your calibration are you totally emptying all the lines (water sample and waste water) prior to connecting them to the KHD?

5) It sounds stupid, but when you empty the KH reagent line (with the pump speed set to 0), it takes forever. I was tempted to change it to pump speed 3 to empty the lines so I didn't have to hold the button so long, but in reading it said that would "void" the calibration. So I just sat there holding the silly button while it emptied.

6) Speaking of pump speeds, you did set them to 3 for the water sample and waste water and 0 for the KH Reagent right? Can you post what you got for actual calibration output rates? You could compare them to mine to see if we're in the same ballpark (37.4 water sample, 4.7 KH reagent, 32.9 waste water).

7) This also sounds dumb, but you double checked that your dosing pumps are assigned to the correct channels in the KHD right?

8) Your last sentence also made me question. You said the only thing between calibration and the test is "emptying the cell and flushing with new liquid." I just want to make sure you're not actually pushing the "empty measurement cell" button, as that isn't part of the setup. After the calibration and draining all the lines (of course refilling the KH reagent line), I believe you're only supposed to push "vent internal reagent tube" followed by "flush measurement cell." But NOT "empty measurement cell completely." That button is only pushed when you need to remove the ph probe.


Again, I'm really not trying to be condescending with any of these questions. These are just the first things that come to mind after going through the setup myself this week. I hope something is possibly helpful.

Good luck!

 

[Dimorb]

So I just setup my own KHD 2 days ago, so I am by NO means an expert. But I have a couple of "silly" things probably for you to check. I know they will sound obvious, but since you didn't mentioned them specifically I'd say it's worth a look.

1) How long is your line from the KH Reagent to the doser? I believe the instructions say something like 27" maximum.

It's 20 cm - max is 70 cm.

2) Did you triple confirm that the KH Reagent lines are totally bubble free? I know in my own case I had an air bubble AFTER the doser (between the doser and the KHD). I had to take the line off and flick it several times to get the bubble out.

Yes. I've tested almost 1000 ml ref reagent - watch many cycles of test's. All tests register a value that's close to the previous. So no jumps only constant lower.

3) With your probe, after you calibrate it did you confirm the actual value in the controller? In the KHD screen itself, near the bottom you can see the current value of the probe. After calibration I put my probe in each reference solution for 4-5 minutes to make sure it read within +/- 0.1 pH of the solution. Just to double check it was working correctly.

Didnt do this - if nothing else pops up I'll try this.

4) Just to double confirm, AFTER your calibration are you totally emptying all the lines (water sample and waste water) prior to connecting them to the KHD?

Yes.

5) It sounds stupid, but when you empty the KH reagent line (with the pump speed set to 0), it takes forever. I was tempted to change it to pump speed 3 to empty the lines so I didn't have to hold the button so long, but in reading it said that would "void" the calibration. So I just sat there holding the silly button while it emptied.

Reagent shouldn't be empty. This is the only line filled from start. They clarifies this in video and manual.

6) Speaking of pump speeds, you did set them to 3 for the water sample and waste water and 0 for the KH Reagent right? Can you post what you got for actual calibration output rates? You could compare them to mine to see if we're in the same ballpark (37.4 water sample, 4.7 KH reagent, 32.9 waste water).

Calibration: water sample 36 ml, reagent 4,2 ml and waste 36 ml

7) This also sounds dumb, but you double checked that your dosing pumps are assigned to the correct channels in the KHD right?

Yes they are.

8) Your last sentence also made me question. You said the only thing between calibration and the test is "emptying the cell and flushing with new liquid." I just want to make sure you're not actually pushing the "empty measurement cell" button, as that isn't part of the setup.

This is a part of the reference solution test - when I want to test the machine with ref solution.

After the calibration and draining all the lines (of course refilling the KH reagent line), I believe you're only supposed to push "vent internal reagent tube" followed by "flush measurement cell." But NOT "empty measurement cell completely." That button is only pushed when you need to remove the ph probe.

Or emptying the machine for test with ref solution.

Again, I'm really not trying to be condescending with any of these questions. These are just the first things that come to mind after going through the setup myself this week. I hope something is possibly helpful.

Good luck!

Im very grateful that someone responded

I found one thing when checking again..

When filling the water sample line (to register value in khd) I found out that the line contains 46 ml but when I empty the line completely and auto dos 46 ml it doesnt fill the entire line.

First I thought there was something wrong with the calibration so re-calibrate but after 3 times with same value (36 ml/min on speed 3) I have to assume there is another problem.

And yes I use calibrated speed when trying to refill the line.

 

[GalaxyBenny]

No worries. See, I told you I was a newbie though, I didn’t know the empty thing for the reference solution.

I haven’t checked what mine actually pumps if I tried to dose a specific amount (namely the volume of the water in the lines). I just used the included tubing and let the app calculator do the math.

Overall it’s really weird (and a bit disconcerting). The reason I went with GHL is I’ve heard their hardware is rock solid, and that just the software connection stuff can be a bit of a pain. I for sure experienced the latter, but I still hope overall the equipment will be reliable. I guess we shall see.

Please keep us updated on what you find. Seems very strange indeed.