Virtually every Sea-Bird Scientific CTD incorporates a pumped flow path, and for good reason: unless the flow rate through the sensors is known and constant, the response time of the conductivity cell will be continuously changing. Without a pump to steady the flow, the CTD is liable to calculate salinity from temperature sampled at depth A and conductivity from depth B. In areas of rapidly changing conditions, depth B could have significantly different properties, leading to severe spiking in salinity and other derived parameters.

To reduce spiking without the loss of resolution caused by data averaging, Sea-Bird Scientific uses a pump and a carefully designed TC duct. The pump provides a constant flow rate and the TC duct aligns the response times of each sensor. So regardless of the CTD’s motion through the water column or battering from the sea, the T and C sensors simultaneously measure the same parcel of water and the CTD retains optimal dynamic accuracy.