**3.4. Electronics subsystem**

In this section the subsystems related to sensor acquisition and conditioning, power electronics and control implementation (Sensor Conditioning, Power Electronics, Feedforward Control, and Feedback Control in Figure 3) are illustrated.

The electronics system architecture is shown in Figure 10. The main characteristic of this architecture is the serial communication input/output line that provides high noise immunity, which can be useful when signals must travel through a noisy environment, such as with remote sensors.

**Figure 10.** Electronics subsystem.

The digital carrier is used like a buffer to provide the proper current level for the serial communication. Here, multiples system buses manage data exchange between the main serial communication core (FPGA) and the communication boards placed on the plant.

The communication boards are provided with one digital-to-analog converter (DAC) and two analog-to-digital converters (ADC). The DAC is a 16-bit, high-speed, low-noise voltageoutput DAC with 30-MHz serial interface that is capable of generating output signal frequencies up to 1 MHz. The ADC is a single channel 12-bit analog-to-digital converter with a high-speed serial interface and sample rate range of 50 ksps to 200 ksps.

### *Control Unit*

The control modules are supported by a DSP/FPGA–based digital control unit. Hence the overall control implementation can be divided between the two digital devices in order to fulfill different requirements: control strategy realization on DSP and serial communication implementation on FPGA.

The overall control strategy is characterized with a nested and decentralized control structure, where only the outer loop is implemented on DSP while the inner current loop is realized on the power module directly. In particular, the outer loop computes the right reference for the inner one starting from required error compensation. The same strategy is applied for each axis.

#### *Sensors Conditioning*

526 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges

Feedforward Control, and Feedback Control in Figure 3) are illustrated.

In this section the subsystems related to sensor acquisition and conditioning, power electronics and control implementation (Sensor Conditioning, Power Electronics,

The electronics system architecture is shown in Figure 10. The main characteristic of this architecture is the serial communication input/output line that provides high noise immunity, which can be useful when signals must travel through a noisy environment, such

The digital carrier is used like a buffer to provide the proper current level for the serial communication. Here, multiples system buses manage data exchange between the main serial communication core (FPGA) and the communication boards placed on the plant.

The communication boards are provided with one digital-to-analog converter (DAC) and two analog-to-digital converters (ADC). The DAC is a 16-bit, high-speed, low-noise voltageoutput DAC with 30-MHz serial interface that is capable of generating output signal frequencies up to 1 MHz. The ADC is a single channel 12-bit analog-to-digital converter

The control modules are supported by a DSP/FPGA–based digital control unit. Hence the overall control implementation can be divided between the two digital devices in order to fulfill different requirements: control strategy realization on DSP and serial communication

with a high-speed serial interface and sample rate range of 50 ksps to 200 ksps.

**3.4. Electronics subsystem** 

as with remote sensors.

**Figure 10.** Electronics subsystem.

*Control Unit*

implementation on FPGA.

The Sensors Conditioning Module provides the output signal from geophone by means of an instrumentation amplifier circuits. The component is configured for dual-channel operation, in order to connect two geophones together. Figure 11, shows the circuit layout for dual-channel. R1A and R1B are the gain setting resistors.

With the ADC input in the range [0-3] V and assuming the maximum magnitude of noise in geophone measurement nearly equal to 1000 m/s, the setting resistors are selected to achieve a gain of 100.

**Figure 11.** Instrumentation amplifier circuits AD8224. R1A and R1B are the gain setting resistors.

#### *Power Electronics*

The Power Electronics Module is based on a trans-conductance amplifier instead of a switching amplifier in order to avoid noise due to the switching frequency. This kind of amplifier operates as a voltage-to-current converter whit a differential input voltage (voltage controlled current source configuration).

The electronics layout that is divided in three main stages: a) the trans-conductance amplifier, b) the current amplifier and c) the feedback resistor.

The power module uses the voltages reference ( ) *Vin* from the control unit to generate the proper current ( ) *LI* to the load (electromagnetic actuator assumed as a RL load). The first stage performs the current control by means of an operational amplifier that is unity-gain stable with a bandwidth of 1.8MHz and it is internally protected against over-temperature conditions and current overloads. The second stage is a classical current amplifier with bipolar transistors in Darlington configuration to increase the current gain. The last stage provides the feedback signal to ensure the desired current in the load. The power supply is in the range of ±30V.
