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6 – MERTIS SHORT TERM

6 – MERTIS SHORT TERM SHUTTER DEMONSTRATOR MODEL P / mN 140 120 100 80 60 40 20 0 0 0.2 0.4 0.6 0.8 f / mm 1 1.2 1.4 1.6 Figure 6.4: Static force measurement of the MSTS FH structure which results in a spring constant of c = 82.3 Nm −1 . f / mm 1.2 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 0 0.5 1 1.5 2 2.5 t / s Figure 6.5: Measured step response of the MSTS DM VCA. The VCA was excited by a symmetric rectangular signal with f = 0.9 Hz. Because of the weak damping ratio D, the transient period is relatively long. 52

Chapter 7 Electronics 7.1 Control Electronics 7.1.1 Power Amplifier The design of the control electronics for the DM was mainly driven by the selection of an adequate power amplifier for the Helmholtz VCA. Two possibilities were dis- cussed named as • push pull Operational Amplifier (OPAMP) and • bridge amplifier. Due to the small attenuation constant of the FH structure and the resulting blade oscillations, relatively high braking currents are required to guarantee the switching mode (fig. 2.1). Therefore, the power amplifier must drive currents in both directions through the coil, which can be realized by a push pull OPAMP. The low required supply voltage of 3.4 V allows maximum driving voltages of ±1.5 V even with rail-to- rail amplifiers 1 . Thus, the coil resistance must be kept small for reaching high driving currents. The coils can favorably be connected in parallel in the Helmholtz VCA setup, which halves the total coil resistance. With the MSTS DM’s Helmholtz coil resistance of RC= 1.712 Ω (tab. 6.3) and the minimum driving current of IC= 1.2 A, a minimum driving voltage of UC = 2.05 V results. Therefore, it is necessary to select a bridge amplifer for the MSTS DM control 1 Note that the supply voltage requirement (tab. 2.1) was changed to 3.4 V during the design phase. 53

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