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posted by  bexnicious on 7/21/2008 11:55:01 PM  |  status: Live  

Sensor Signal Conditioning

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Question Details:
The figures below show a circuit to condition the signal of a given sensor. Lets assume
that the sensor signal is vsensor = 1.8 + 0.3 sin (120*pi*t)[V]


a) What should the values {Vref ;RS;RF ; VS} be, such that we eliminate the sensor
offset (1.8[V]) and amplifies the signal in the range ±5[V] to be fed into an A/D
converter for data logging.
b) If the signal has noise above 1[kHz], design a passive low-pass filter (or augment
the circuit above - active low-pass filter) to reduce the noise in the signal.

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posted by shann(EE-SME) on 7/22/2008 3:37:52 AM  |  status: Live
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Response Details:
Given sensor signal
We need to eliminate the sensor offset voltage 1.8 and amplify the remaining sinusoidal voltage to range.
Given circuit diagram is differential amplifier.
Output voltage expression


From the above expression we can say that the following two points to get the required constraints.

1. For elimination offset voltage(1.8) we have take
      ................ (1)
 
2. For achieving a gain range of   we need to consider that
      ..................... (2)
 
From equation (2) we can get
Consider , then
 
Now equation (1) becomes
So to achieve all conditions mention in part (a), we have to take the parameters as like below:
 
;
;
 
I hope this helps you a lot.............................
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