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sensor excitation circuit help

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hemnath

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Please find the attached circuit. What is the purpose of MAX4524 in this circuit?
 

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  • sensor circuit.pdf
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Hi,

It is a MUX.

0: measure excitation current across 100R
1: measure sensor output signal
2: zero. (I assume for offset adjust)
3: unused.

Klaus
 
Yes I agree. How offset can be adjusted? What is the logic behind this. Please explain in detail.
 

Hi,

It switches to "offset", where the input is shorted and the ADC should read zero.
But because of offset it measures any other value. Let's name it "Z".

Now with every "true" measurement it simply subtracts the offset.

CorrectedValue = ADCValue - Z

Klaus
 
1. Is it measures the opamp offset voltage?
2. Resistor 100E is 0.01% tolerance FOIL type used. What is the purpose of it. Why excitation current is to be measured?
 

Hi,

1) it measures the system offset voltage: multiplexer, OPAMP, ADC
2) Where do you have the information "FOIL"? Are you hiding additional infromations? (I don´t see the necessity for "foil")

Why: Because the sensor output is ratiometric. It depends on excitation current. And it shows if the sensor is connected at all.

Please read basics about "strain gauge sensors" in four wire connection.

Klaus
 
This is the resistor used. Vishay Y1622100R000T0L , RES 100 OHM 8W 0.01% TO220-2.
 

Sorry the resistor used is Y1453100R000T9L, 100 Ohm ±0.01% 0.6W ±0.2ppm/°C Through Hole Resistor Radial Moisture Resistant, Non-Inductive Metal Foil .

Why this precision resistor is used?
 

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