To ensure flat frequency response characteristics, some models of acceleration transducers have oil sealed inside. The viscosity of the oil is adjusted to make the frequency response flat at 23��C. Changes in viscosity due to temperature changes affect the frequency response and phase characteristics. Though a silicone oil which the viscosity hardly changes is adopted, the frequency response characteristics of the transducer are affected by temperatures as shown in the figure below. Thus, for accurate measurement in a frequency zone exceeding one-tenth the stated frequency response range, the temperature of the transducer should be kept around 23��C .