2.1 Doser - Automatic adjustment but with no control

[kingy138]

Hi,

My KH has been pretty stable for a few weeks, but this morning I noticed a minor drop, on investigation I found that my doser automatically adjusted the dose by -0.2ml.
Although I do have a KHD, I am not using dosing control, the doser is setup on a manual schedule.

My schedule is for 0.5ml per dose.
Please see screenshot below.

Could this be because the pump cannot handle this precision over a long duration, and is then automatically corrected to bring the dose inline?
For example, although it was set to 0.5ml, could it really have been dosing 0.51ml, which the doser can calculate based on the flowrate, it then later corrects this situation?

If my assumption is correct, it would be a great feature to actually show this to the user in the UI. Showing the "calculated dosage" based on the flowrate, would allow the user to understand this will happen and give them the option to adjust the dosage.

12437

[Thilo]

If there is no control configured, this adjustments appear because of a rounding issue. This has to do with the dosing duration, which from time to time takes 10ms longer or shorter and we can't change anything there.
But normally this should result in a displayed adjustment of +/-0.1ml, since the difference at the actual dosing is lower than 0.1ml.

Which dosing speed have you set? The actual difference could be greater if the pump speed is higher. For maximum accuracy for such low dosing volumes, speed 0 should be used.

[kingy138]

Thanks Thilo.
That makes sense and aligns with what I thought it was doing.

I have the doser set to speed 1, I had previously been using speed 0, but I'm finding that air bubbles keep finding there way into the line, for reasons I cannot figure out, I was hoping that upping the speed might help, but it doesn't.

It's almost like the liquid is flowing backwards, but I am using a one way valve on the line to prevent this. I've also just changed the doser tubes, as I thought they might be old and maybe allowing the liquid to flow back.

Sadly I have no other option but to have the doser lower than line into the tank.

[Thilo]

It's almost like the liquid is flowing backwards, but I am using a one way valve on the line to prevent this.

If this is really the problem for the air bubbles, the pump head could be the problem. You could check this by using one of the other pumps.
Else you could use PVC-tube instead of silicone-tube, because experience has shown that fewer air bubbles are formed there.

[kingy138]

Again, thank you sir.

That's interesting about the PVC tube you mention. I'm dosing with all four heads Triton, the first head actually uses PVC, as I had some spare, the other three use silicone and only the silicone ones have issues.

I'll look to get some more PVC I think and see how things go.

Many thanks,
Davew

[ispookie666]

Silicone is around 1000 times more permeable to air than pvc [emoji4]

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