General Information
To ensure reliability in service, the multilayer actuators are comprehensively tested under the following conditions:
| Test | Conditions | Level |
|---|---|---|
| Displacement | At max operating voltage | AQL |
Capacitance & Tan.gif){kind=small} | 120Hz, 1Vrms | 100% |
| Insulation Resistance | At max operation & voltage | 100% |
Handling
Multilayer actuators are made of ceramic and may be damaged if subjected to excessive physical or thermal shock.
Operating Environment
As voltages of up to 300 V (d.c.) may be employed, it is necessary to ensure that the actuators do not come into direct contact with moisture. Never use high voltages in the vicinity of inflammable liquids or gasses.
Mounting Multilayer Actuators
Devices may be attached using an epoxy resin adhesive that cures at temperatures below 75°C. To obtain maximum displacement and stiffness from the actuator, the bond thickness should be minimised. The mounting fixture must be designed to ensure that no shear or tensile stresses are placed on the actuator. It is preferable that the actuator is always compressively stressed.
Driving of Multilayer Actuators
During the manufacture of these devices, a d.c. voltage is applied to polarize the ceramic (analogous to the magnetization of magnets). Either d.c. or a.c. Voltage can be used, although the voltage should not be greater than 1/8 the rated voltage in reverse polarity, in order to avoid polarization switching. In order to permit driving of the actuator under an a.c. field without the polarization direction switching, a d.c. bias field may be applied in the positive direction. The use of a.c. driving signals will induce a temperature rise, which will increase as a function of frequency. The temperature rise must be controlled to avoid the heating beyond 75°C. As multi-layer actuators have a relatively large capacitance, the upward response time depends upon the current rating of the power supply. For a rapid downward response, the discharging of the actuator is rate controlling. The maximum charging / discharging current must not exceed 5 Amps.
