Mosaic
Well-Known Member
Hi:
Can anyone with a simulator help develop the LM258 Opamp circuit to convert an LM335 absolute temp sensor output to celsius?
The LM335 outputs 10mV per deg Kelvin.. so it's output is about 2.73V at 0 Deg C.
I'd like the opamp to do 2 things.
1) Common mode reject 2.43 V, so at 0V out the actual temp is -30 DegC.
2) Amplify the signal so that the lm258 outputs perhaps 3.5V at 57.5 degC.
That means the 87.5 deg C swing requires 40mV per deg C, or a 4X signal amplification.
With an 8 bit ADC referenced at 5V ...this translates to 2 bits per deg C accuracy.
I want to use the 8 MSB of a 10bit ADC to reduce error due to elec. noise as the opamp has to drive the signal about 5' thru an automotive harness.
The opamp will output via a 1K then via the harness wire then to the PIC ADC via another 1K, to protect against a harness short to 12V.
3.5V is the full voltage swing of the lm258 at single rail +5Vdd.
Can anyone with a simulator help develop the LM258 Opamp circuit to convert an LM335 absolute temp sensor output to celsius?
The LM335 outputs 10mV per deg Kelvin.. so it's output is about 2.73V at 0 Deg C.
I'd like the opamp to do 2 things.
1) Common mode reject 2.43 V, so at 0V out the actual temp is -30 DegC.
2) Amplify the signal so that the lm258 outputs perhaps 3.5V at 57.5 degC.
That means the 87.5 deg C swing requires 40mV per deg C, or a 4X signal amplification.
With an 8 bit ADC referenced at 5V ...this translates to 2 bits per deg C accuracy.
I want to use the 8 MSB of a 10bit ADC to reduce error due to elec. noise as the opamp has to drive the signal about 5' thru an automotive harness.
The opamp will output via a 1K then via the harness wire then to the PIC ADC via another 1K, to protect against a harness short to 12V.
3.5V is the full voltage swing of the lm258 at single rail +5Vdd.