CVP causes noise through the MEA-PGP perfusion chamber

Hello,
I'm using a perforated MEA with a 2-way peristaltic pump meaning, that I have a perfusion from the top and one from the bottom. I also use two different tubes with a different diameter and the original MCS CVP-Pump. The peristaltic pump is set to approx. 5 ml/min and the CVP-Pump to 20 mbar.
To test the noise-level of the MEA I filled it with ACSF and as long as I only use the "top-perfusion" everything is ok: The Noise level in the RAW-recording is about 60µV from peak to peak. When I start the CPV-pump and open the bottom-perfusion a huge noise appears: up to 1000µV peak to peak. When I close the bottom perfusion again and shut up the CVP-Pump the noise remains. It seems, as long as the MEA is dry from underneath there is no noise, but when the bottom-perfusionchamber is filled with ACSF there is this big noise.

Can you help me with this problem? Is this way of testing the right way? Is this noise due to some flow through the perforation? In the actual recording the slice covers the MEA perforation, so will this noise disappear?

I also have some fotos, but I don't know how to insert fotos here. "Host an image" doesn't seem to work.

Felix

Dear Felix,
please drop me a line at "support@multichannelsystems.com", there you can also send the photos. My suspicion is that the lower perfusion cycle is not grounded , but I'd also need to send some pictures to illustrate how to ground it.

Frank MCS