Design a position DAS using a sensor, analog electronics, and a Freescale microcomputer with an 8-bit ADC. Let x be the position to be measured (Figure 12.65). The input range is -1 to +1 mm, and the signals of interest are 0 to 1 Hz. A LVDT will be used to convert position x into voltage y. When the input position is -1 mm, the LVDT output y is -100 mV. When the input position is zero, the LVDT output, y, is zero. When the input position is +1 mm, the LVDT output y is +100 mV. In between, the voltage output is linearly related to the position. A REF02 precision reference will provide the constant +5.00 V for your analog circuit and the microcomputer ADC.
Figure 12.65
a) What is the transducer sensitivity? Give units.
b) What is the transfer relationship required to convert y into z1?
c) What is the maximum allowable noise for your analog circuit? Refer the noise to the amplifier input and give units.
d) Choose an appropriate sampling rate
e) Design the preamplifier which has the following characteristics: single input (not differential), gain so that the 0 to +5 V ADC is used, high Zin, low Zout, bandwidth > 200 Hz. Show resistor values, but not pin numbers. You may use any analog op amps, but please include the chip number.
f) The signals of interest are 0 to 1 Hz. There is unwanted noise at 60 Hz. Add a two-pole low-pass filter with a cutoff of about 10 Hz.
g) What is the system resolution in millimeters?
