Salinity Probe Variation

[Mark Lang]

My salinity probe reading shifts when my heater is on. Above chart is Probe vs Heater Watts. You see every time the wattage increases for heating (gray) the Salinity measurement moves up. When heat is off, it gradually moves down. I calibrated the probe again last night and use temp compensation of 2.2. A check after calibration put it spot on at 35ppt. The Probe Cable runs on a route away from all other cables. The heater and probe are in the same sump chamber (return).. I can't move the probe because of micro bubbles in other chambers.

I'm thinking I may have one of two issues; stray current from the heater or effect of temperature increase/decrease in the chamber.

I think I need to check again for stray current when the heater is on. I checked a couple weeks ago and found to to be so low it barely registered. But I can't say for sure about heater state.

I'm looking for other suggestions or things I can check.

TIA

 

[P-Dub]

My salinity probe reading shifts when my heater is on. Above chart is Probe vs Heater Watts. You see every time the wattage increases for heating (gray) the Salinity measurement moves up. When heat is off, it gradually moves down. I calibrated the probe again last night and use temp compensation of 2.2. A check after calibration put it spot on at 35ppt. The Probe Cable runs on a route away from all other cables. The heater and probe are in the same sump chamber (return).. I can't move the probe because of micro bubbles in other chambers.

I'm thinking I may have one of two issues; stray current from the heater or effect of temperature increase/decrease in the chamber.

I think I need to check again for stray current when the heater is on. I checked a couple weeks ago and found to to be so low it barely registered. But I can't say for sure about heater state.

I'm looking for other suggestions or things I can check.

TIA

I am frankly surprised that you have anything close to an accurate reading with the conductivity probe. Mine has not read anything close to accurate for longer than a few hours since the first installation and many calibrations. Mine is now reading 29.5 and was just recalibrated for the 5th time the other day.

 

[Samina]

Agree with above. You are doing pretty good if you have such a close range to it being accurate. I would have to calibrate daily if I wanted to rely on the salinity readings from the probe. I only use it to monitor the trend and not to determine the actual conductivity.

But on a side note, it you are worried about a stray current, do yourself a favor and get a grounding probe. But honestly, I don’t think that’ll do much for the conductivity probe. I just think it is good to have a grounding probe just for safety purposes.

 

[Mark Lang]

I have observed that if the probe provides what seems like unreasonable results by trending up or down when I am reasonably certain my salinity theoretically can't be moving, there have been one of two conditions:
1. Air bubbles in the sensor. (highly likely the culprit)
2. Probe cable is touching or in close proximity to hardware or another cable.

My chart from yesterday points to another condition that might be temperature related, or proximity to hardware related. I just need to sort that out, probably by moving the heater to another chamber if I can find room.