KHD director.jpg

My new KHD SA doser is running for 3 weeks.

Up to the first arrow, the measurements were comparable to the hanna. the latter measured between 8.0 and 8.2 throughout the photoperiod.
It is of course the intention that I stop with the hanna, once I have confidence in the KHD.

The day before the first arrow, the measurements were all 8.1. No problem, but normally there is a slightly declining trend during the day and a slightly rising trend at night. Which is normal of course.
So I flushed the measuring cell 2x from GHL connect, nothing else.
Then the measurements suddenly became 0.5 KH lower?

The next 2 days the readings continue to decrease slightly. Since there is some variation in the calibration of the pumps in the beginning, I recalibrated all three pumps at the 2nd arrow. Pump 1 and 3 deviate 2ml and the reagent pump 0.2. So adapted.
The Ph probe also suddenly checked, but it was ok. Both with 4 and 7 calibration fluid, the deviation was both 0.02. negligible.
After the recalibration, the KH fluctuates around 7.2.

So today at arrow 3, I ran some reference tests with KH 7.5.
Results : 6.9, 6.7, 6.6 and 6.6.
You can forget the first one, that is a mixture of aquawater/ref liquid.
Actually, I think that is a far deviation from 7.5, but I will correct this via the correction factor. +13%.
Then the very strange thing comes, back 2x the measuring cell rinsed and some aqua measurements made. 8.9, 8,6 and 8.7 .
No other adjustments made, so the correction factor has been removed from arrow 4.
Now the measurements are back 7.9, 7.8,...

You would think that if you only run some reference tests and rinse the measuring cell, you would get the same value afterwards as for the ref tests? This is 0.8 difference. remains strange.

Pump 1 empties its suction tube completely with the set value.
Pump 3 certainly drains the measuring cell.
There are no bubbles in the pipes of the 3 pumps.