A sensor assembly can include a gyroscope, an accelerometer, and a housing assembly containing the gyroscope and the accelerometer. An axis of the gyroscope can be collinear with an axis of the accelerometer. A method of inspecting a well pumping unit can include attaching a sensor assembly to the pumping unit, recording acceleration versus time data, and in response to an amplitude of the acceleration versus time data exceeding a predetermined threshold, transforming the data to acceleration versus frequency data. A method of balancing a well pumping unit can include comparing peaks of acceleration versus rotational orientation data to peaks of acceleration due to circular motion, and adjusting a position of a counterweight, thereby reducing a difference between the peaks of acceleration due to circular motion and the peaks of the acceleration versus rotational orientation data for subsequent operation of the pumping unit.