Waste volume doesn't equal sample+reagent

[kingy138]

I have very accurately (painstakingly) calibrated all dosing heads, and I'm finding that the accuracy is aligned with my expectation.

The issue I've found is that the waste volume doesn't make any sense, it's ~50ml per measurement too high. Albeit I don't know how much reagent is actually used, it cannot be too much, maybe a few ml.
I know that it washes out the test vessil before it executes measurement, but this is small volume too.

Either way, it doesn't add up.

I've measured the waste volume physically in the container and it's significantly less than what the dosing head thinks should be in the container.

I think this is caused as at the end of each measurement, the test vessil is emptied, the pump continues to run for a period dry, I guess this is to ensure all liquid is removed and clear of the tubes.

Is this normal?
If it's normal and just how the waste dosing head works, then I'm happy, this isn't a complaint, this is me worried I've done something wrong.

[Vinny]

Yes, it is normal.
This happens because the KHD will always drain a bit longer to ensure the cell is prepared for the next test. During this process, there will be some air in the drain tube. That causes the difference shown in the waste volume.

[kingy138]

Cheers Vinny my lad.

As a mega nerd, I timed the dosing pumps to calculate how much running dry would equal in liquid.
Within a small margin, it adds up correctly.

[Adri-DSR]

I have read the reason why the waste pump shows more then there really is in the waste container but this makes no sense. The waste pump at my side shows almost full and gives an alarm while the container is just half full. Why show and calculated and give an alarm while the numbers totally does not add up at all. 50% less is a too big difference.

This should and could be better than it is now.

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[kingy138]

Agreed, this absolutely should be better than it is now.
They need an automatic compensation calculator to adjust it.

My solution, as crude as it is, was to simply increase the capacity of the waste container to account for the difference.
I don’t care about the absolute volume anyway, I just want notification when it’s near full, so this works fine for me.