Advance preparation begins with removing the sensor from its polystyrene box and plastic bag, and examining for loose screws on the mounting frame and motor, and for any other possible damage. The pump is connected to the tester and turned on, and the current drawn by the pump is measured. If the current is too high—above 100-120 mA, depending on model—the sonde must be rejected, and a new instrument prepared. Once correct current is attained, the pressure and vacuum provided by the pump are checked, and then the sensor is conditioned with high O3 for 30 minutes.