A portable dissolved oxygen meter is an instrument for at-line monitoring of dissolved oxygen in an industrial process. They are commonly used to do testing of DO concentration in a process at locations where a continuous, in-line DO sensor is not required or possible. They can also be used at sampling points near an in-line DO sensor to verify that the sensor is correct, and to calibrate the in-line sensor. METTLER TOLEDO's primary portable dissolved oxygen meter is the InTap portable optical dissolved oxygen analyzer.