Signal Conditioner for Piezoelectric Sensors

This is a simple signal conditioner circuit for Piezoelectric sensors. The circuit converts the input charge to voltage and the level shifts to the ADC input range of 0.1 V to 2.4 V. The circuit is built using AD8608 OPAMP from Analog devices. Piezoelectric elements are used to construct transducers for a vast number of different applications. Piezoelectric materials generate an electrical charge in response to mechanical movement, or vice versa, produce mechanical movement in response to electrical input. The board shown here is suitable for the Kistler type 8002K sensor. The K8002K is a high-precision accelerometer for shock and vibration measurements.

Piezoelectric elements are commonly used for the measurement of acceleration and vibration. Here, the piezoelectric crystal is used in conjunction with a seismic mass m. If the mass is subjected to acceleration a, then there is a resulting inertial force F = m × a acting on the seismic mass and the piezoelectric crystal. This results in the crystal acquiring a charge q = d × F, where d (measured in Coulombs/Newton, C/N) is the crystal charge sensitivity to force.

The first stage of the signal conditioning circuit is a charge amplifier (U1A and capacitor C2), The output of the circuit is shifted to handle bipolar input signals (for example, vibration measurements). The zero of the circuit is shifted to the middle of the input range of the ADC, using a reference of 1.25 V. The second stage of the signal conditioning circuit is a non-inverting amplifier which provides the output.

Reference Voltage approx. 1.25V is generated through resistor dividers R9 and R11. An optional chip U2 TLV431 SOT23-3 can be used for accurate reference voltage. The circuit is from the Analog Device’s Application Note. Considering the tolerances of the parts, the minimum output voltage (low limit of the range) is set to 100 mV to allow for a safety margin. The upper limit of the output range is set to 2.4 V to give 100 mV headroom for the positive swing at the ADC input. Therefore, the nominal output voltage range of the input op amp is 0.1 V to 2.4 V.

Features

• Supply 3.3V DC
• Output 100mV to 2.4V
• On Board Optional Reference Chip
• On Board Power LED
• PCB Dimensions 26.35 x 14.92 mm

Sensor (Kistler Type 8002K Quartz Accelerometer)

Type 8002K is a high-precision accelerometer for shock and vibration measurements in laboratory applications. Its excellent performance is derived from an ultra-stable crystalline quartz sensing element. Contained within the housing is a piezoelectric assembly consisting of a seismic mass preloaded to a quartz element stack. The force acting on the quartz measuring element is proportional to the acceleration following Newton’s Law: F=ma. This element, in turn, gives an electrical charge signal proportional to the force, and therefore, to the acceleration. The charge signal is conducted through a low-noise coaxial cable, such as the 1631 series, and then converted and amplified to a proportional output voltage in a charge amplifier (such as Type 5010). The 8002K accelerometer is a special version with an emphasis on transverse sensitivity and amplitude non-linearity. The 8002K along with a 5022 Charge Amplifier form.

Connections

• CN1: Pin 1 = VCC, Pin 2 = Negative, Pin 3 = Positive, Pin 4 = NC, Pin 5 = GND
• CN2: Pin 1 = VCC, Pin 2 = Output, Pin 3 = GND
• D1: Power LED

Schematic

Parts List

Connections

Gerber View

Photos

Video

AD8608 Datasheet

Please follow and like us: