The current application discloses assemblies and methods for monitoring the downhole condition of a subterranean formation subject to a treatment such as hydraulic fracturing. The method comprises deploying a sensor to a position proximate to the treatment zone of the subterranean formation, maintaining the sensor below or within the flow path of the treatment fluid applied to the treatment zone, and recording a measurement by the sensor. In some cases, the sensor is hosted in an elongated housing and the outer diameter of the elongated housing is about 10% to about 70% of the inner diameter of the flow path of the treatment fluid applied to the treatment zone. In some cases, the flow rate of the treatment fluid is controlled. Therefore, the conveyance device of the sensor can be protected from damage or breakage caused by the erosion, jetting effects or drag force of the treatment fluid.