I'm looking at the history on a PH probe. I have it set to record values every 15 minutes. I'm seeing that it sometimes does that, but frequently misses one or more values, sometimes going for as long as an hour between successive entries in the log. Is anyone else seeing this? It seems like somehow the communications channels is down sometimes, but even if that's what's going on, it should just queue up the logging attempt and keep trying...
Intermittent history
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Gaël
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Hello Dave,
See https://www.aquariumcomputer.com/knowledge-base/how-to-record-probe-values/
Measurements are NOT recorded…
If your current sensor value is the same as the previously saved value. For example, if your pH value was previously recorded at 8.0 and the actual pH value is still 8.0 at the time of the recording…this value will not be recorded again since it has already recorded the same value. This is done to improve storage efficiency.
Gaël
See https://www.aquariumcomputer.com/knowledge-base/how-to-record-probe-values/
Measurements are NOT recorded…
If your current sensor value is the same as the previously saved value. For example, if your pH value was previously recorded at 8.0 and the actual pH value is still 8.0 at the time of the recording…this value will not be recorded again since it has already recorded the same value. This is done to improve storage efficiency.
Gaël
That makes sense, but it doesn't appear to be true. I have many successive values in the history with the same reading. I don't see any pattern that correlates the value with whether or not history is saved. Here are the last 14 readings. Sometimes there are successive entries with the same value.
| 4:15 | 8.19 |
| 4:30 | 8.18 |
| 5:00 | 8.18 |
| 5:45 | 8.17 |
| 6:00 | 8.18 |
| 6:45 | 8.17 |
| 7:00 | 8.18 |
| 7:15 | 8.17 |
| 7:45 | 8.16 |
| 8:00 | 8.16 |
| 8:45 | 8.15 |
| 9:00 | 8.15 |
| 10:00 | 8.15 |
| 11:00 | 8.16 |
In order to understand this - I´ll think you need to go deeper into how a electronic pH device works. It is in reality a mV meter there 0 mv = 7 in pH. At pH 7 the H⁺ and the HO⁻ ions are equal in numbers -> the potential between them is 0. If there is more HO⁻ ions than H⁺ ions the potential is negative and if H⁺ ions is more than the OH⁻ ions - the potential is positive.
Its a linear curve and every pH step is a rise or a decrease with a certain mV - the slope. In the old days 56 mV was a common slope - it means that for each whole pH step - the mV was altered 56 mV. Its an inverted curve - above 7 is minus and below 7 its plus.
With this theoretical slope (56 mV) pH 6 will be 56 mV and pH 8 will be -56 mV . When you calibrate your pH meter - the 7 solution determines where your real electrode shows 0 mV and the pH 9 solution determines your slope (the slope of the curve in mV/pH unit) Let's say pH 9 is -120 mV - then your real slope is 60 mV/full pH step. If the mV reading is - 60 mV - your pH is 8.
pH = 8.15 in this case means 69 mV. But looking at the calibration process - I suspect the GHL use a more precise measurement system of the mV signal which probably allows detection in at least 0.1 mV step. 69.1 mV will in this case means 8.152 in PH and 68.9 mV will stand for 8.148. If GHL meter relay on the mV value in order to decide if it should plot a figure or not - both will be 8.15 but the real measurement (mV) has change. 69.1 is another value than 68.9 but both report 8.15 because of abbreviation rules when you use a two digit decimal.
But I do not know - its only what I suspect as the explanation
Sincerely Lasse
Its a linear curve and every pH step is a rise or a decrease with a certain mV - the slope. In the old days 56 mV was a common slope - it means that for each whole pH step - the mV was altered 56 mV. Its an inverted curve - above 7 is minus and below 7 its plus.
With this theoretical slope (56 mV) pH 6 will be 56 mV and pH 8 will be -56 mV . When you calibrate your pH meter - the 7 solution determines where your real electrode shows 0 mV and the pH 9 solution determines your slope (the slope of the curve in mV/pH unit) Let's say pH 9 is -120 mV - then your real slope is 60 mV/full pH step. If the mV reading is - 60 mV - your pH is 8.
pH = 8.15 in this case means 69 mV. But looking at the calibration process - I suspect the GHL use a more precise measurement system of the mV signal which probably allows detection in at least 0.1 mV step. 69.1 mV will in this case means 8.152 in PH and 68.9 mV will stand for 8.148. If GHL meter relay on the mV value in order to decide if it should plot a figure or not - both will be 8.15 but the real measurement (mV) has change. 69.1 is another value than 68.9 but both report 8.15 because of abbreviation rules when you use a two digit decimal.
But I do not know - its only what I suspect as the explanation
Sincerely Lasse
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