Filter Roller vs. Conductivity

[jtm235]

Wondering if there are any scientifically inclined people out there who can solve this curiosity...Every time my filter roller runs, I get about a 5 minute dip on my conductivity probe. My conductivity meter registers approximately a 1.0 ms/cm dip for 4-6 minutes after my filter roller rolls. My filter roller runs for 0.75 seconds when the "high" level sensor is triggered inside the roller's intake chamber. The filter roller is plumbed directly from the overflow. The attached photo shows 2 dips in conductivity after 2 separate rolls. The corresponding sump level spikes represent the water volume transferring from the roller chamber to the return chamber, approximately 250 to 400 ml. My theory is organics from the roller chamber get released through the fresh roller fleece, and this lowers conductivity maybe? It's not an issue or anything...just curious and looking to understand as much as possible.

 

[KStatefan]

Electrical interference

 

[Randy Holmes-Farley Verified Community Expert]

I think it has to be an electrical interference issue. Nothing is added or removed by a roller fleece that would significantly impact conductivity.

 

[jtm235]

I think it has to be an electrical interference issue. Nothing is added or removed by a roller fleece that would significantly impact conductivity.

I thought electrical interference at first as well...but the dip is for 5 minutes...Also, I have the conductivity circuit fully isolated with one of these:

https://atlas-scientific.com/electrical-isolation/

 

[Randy Holmes-Farley Verified Community Expert]

You can try measuring tank water conductivity outside and away from the tank, before and after rolling.

 

[rhitee93]

Is the water level on your conductivity probe changing very much after the roll advances? I would be more inclined to think this had something to do with disturbing the water boundary layer around the pins in the probe.

 

[jtm235]

Is the water level on your conductivity probe changing very much after the roll advances? I would be more inclined to think this had something to do with disturbing the water boundary layer around the pins in the probe.

Yes, the water level in the return pump chamber is rising 0.25" to 0.5" after the roll, however the conductivity meter is plumbed inline on the return feed:

https://atlas-scientific.com/probes/industrial-conductivity-probe-k-1-0/

 

[jtm235]

You can try measuring tank water conductivity outside and away from the tank, before and after rolling.

Good idea...unfortunately I don't have an external cond. meter to use :(

 

[rhitee93]

Yes, the water level in the return pump is rising 0.25" to 0.5" after the roll, however the conductivity meter is plumbed inline on the return feed:

https://atlas-scientific.com/probes/industrial-conductivity-probe-k-1-0/

Wow, that is difficult to explain. I was a test engineer for a lot of years, and industrial instrumentation was my thing. I've seen a lot of example of noise in measurements, but can't explain this one.

You don't happen to get a period of micro-bubble flow associated with the roller advancing do you?

The time constant seems all wrong for this to be electrically induced noise.

 

[Randy Holmes-Farley Verified Community Expert]

You could trigger the roller a few minutes after a fresh one rolls into place to see if it is a movement effect, or if it relates to what is on the roller.

 

[jtm235]

Wow, that is difficult to explain. I was a test engineer for a lot of years, and industrial instrumentation was my thing. I've seen a lot of example of noise in measurements, but can't explain this one.

You don't happen to get a period of micro-bubble flow associated with the roller advancing do you?

The time constant seems all wrong for this to be electrically induced noise.

No discernable micro bubbles from the roller...But perhaps the filter roller is dumping organics into the sump, then affecting the protein skimmer (downstream) in a way where it ejects more micro bubbles maybe? I would think this should be a noticeable difference if I inspected the output from the skimmer. I will do a test and report back! (insert nerd emoji here)