Designing Engine Control System - Circuit Interface for Accelerometer 3028

Advantages and Disadvantages of 3028 Accelerometer

You are designing an engine control system. One of the control inputs for this system is the vibration level of the engine. You have selected a Measurement Specialties 3028 accelerometer (±10g version).

Its datasheet is available on the ELEC6208 course website. You need to design a circuit to interface with it, amplify the signal, filter out unwanted vibration frequencies, and introduce as little amplitude distortion as possible. It needs to connect to a data acquisition unit with an input impedance of 100?.

 

You should assume that you have access to a +5V power supply.
You should address the following points, and document them in a report:

 

1. What are the advantages and disadvantages of this type of accelerometer? What type(s) of interface circuit would be suitable for this device? What are the important parameters to consider?

 

2. Find the (simplified, ideal) equivalent circuit of the accelerometer, and simulate it at a reasonable range of frequencies and amplitudes to verify the behaviour of its differential outputs. You are encouraged to do this in NI Multisim, but you may also use MATLAB or another SPICE simulation package. You should set up the simulation so that the input vibration amplitudes and frequencies can be easily varied. You should assume that the resistances are precisely matched, and the sensitivity is in the centre of the range specified in the datasheet.

 

3. Connect the outputs from the accelerometer to a differential amplifier, and the amplifier output to the 100? resistive load. You should choose appropriate components to increase the sensitivity to 100 ±5 mV/g, and explain why you chose this op-amp and the values of other components. Analyse and document the circuit’s performance.

 

4. Replace the differential amplifier with an instrumentation amplifier (you should construct this from individual op-amps, rather than using a dedicated instrumentation amplifier component). Again, choose appropriate components. Analyse and comment on the performance of the circuit.

 

5. Evaluate the performance of the both amplifier systems when the accelerometer piezoresistance values are unmatched. You should present this both theoretically (for an ideal circuit) and with simulation.

 

7. The control system is only interested in vibration in the range 20-170 Hz; you should add an active filter to your circuit so that unwanted frequencies are removed. The priority is to have as little amplitude distortion as possible in the pass-band. You should achieve a roll-off of around - 40dB/decade. You are expected to explain your design, please do not use automated filter design tools for this. Present tests for the complete system, at a range of input frequencies to confirm that the system performs as designed.

 

8. Evaluate the overall current draw of the system. Improve this, but maintain the required sensitivity.
What did you change? How has it affected performance?