Specifications

E-500/E-501 Series PZT Servo Controllers User Manual PZ 62E
Release 2.15.1 www.pi.ws Page 65
Fig. 36: Interdependency between the mean MTTF of a PICMA® actuator and the relative
humidity
Example
The simple formula MTTF = AU * AT * AF provides a quick estimate of the reliability in
hours. In concrete terms: The values for 75% RH ( AF=14), 100 VDC (AU=75) and 45 °C
(AT=100) result in an approximate MTTF of 105,000 h, i.e. more than 11 years (see
markings on the diagrams).
Read the “Tutorial: Piezoelectrics in Positioning” in the PI Catalog for detailed information.
10.2. How to Measure the Amplifier Output of E-504 Modules
The innovative, efficient circuitry of the E-504 amplifier module reduces power consumption
and heat dissipation, especially in dynamic applications. Working with an internal switching
frequency of 100 kHz, charge is transferred to the piezo actuator using low-loss PWM
techniques. The ripple of the amplifier output is <100 mVpp at 100 kHz. But when
measuring the amplifier output signal with low sampling rate and small bandwidth (e.g. with
a digital oscilloscope), aliasing will occur and distort the measurement result. In digital
signal processing, aliasing refers to an effect that the signal reconstructed from samples is
different than the original continuous signal when the sampling rate is too low. With the E-
504 amplifier output, this means that a low-frequency signal seems to be measured which
is not present at all.
Example:
When a 91 Hz signal is sampled with 100 Hz sampling rate, the result seems to be a 9.1 Hz
signal (see figure below).
Fig. 37: Signal digitization with too low sample rate (time in 1/100 s): Original signal = 91 Hz
and sampling rate = 100 Hz; the result is mistaked as a 9.1 Hz signal (“Alias”)
To avoid aliasing, the sampling rate must be at least twice as high as the highest frequency
in the signal to be sampled (according to the Nyquist–Shannon sampling theorem). I.e. with
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