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Temperature Effects
Two effects must be considered:
a) Linear Thermal Expansion
Thermal stability of Piezo ceramics is better than most other materials (steel, aluminum etc.). It is characterized by the coefficient of thermal expansion (CTE, a) which specifies relative change in length DL/L per unit change in temperature. The following values apply to HVPZT and LVPZT ceramics used in PI piezo actuators:
HVPZT ceramics : a » 11 * 10-6/K
LVPZT ceramics: a » -3.5 * 10-6/K
The CTEs change with temperature, the values given above are valid for room temperature.
b) Temperature Dependency of the Piezo Effect
Piezo translators work in a wide temperature range. Since the piezo effect is based on electric fields it functions down to zero degrees Kelvin. For several reasons the magnitude of the piezoelectric effect (piezo gain) is dependent on the temperature; however around room temperature it is very stable. At cryogenic temperatures it reaches approximately 20 to 30% of its room temperature value. See Fig. 4.36/1, for temperature dependency.
Temperature dependency of the piezo effect.
Piezo ceramics must be poled to exhibit the piezo effect. During polarization the ceramic is heated (to allow alignment of the dipoles) and an electric field is applied. Conversely, a poled Piezo will depole when heated above the maximum allowed operating temperature. PI HVPZTs have a Curie temperature of 300° C and can be operated up to 150° C (with P-702.10 high temperature option). LVPZTs show a Curie temperature of 150° C and can be operated up to 80° C. See "Options" at the end of "Piezo Actuators" section for temperature range modifications.
Note:
Closed loop piezo positioning systems are less sensitive to temperature changes than open loop systems. Optimum accuracy is achieved if the operating temperature is identical to the temperature during calibration (22° C). See calibration test sheet for details.
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