Problem with scaling for ADC

Status
Not open for further replies.
G

garg29

Advanced Member level 1
Joined
Nov 17, 2004
Messages
443
Helped
25
Reputation
50
Reaction score
10
Trophy points
1,298
Activity points
3,593
scaling for adc

Dear freinds

i have drawn this circuit for amplifying the signal of temperature sensor LM35.i am using adc0831 .since LM35 gives 10 mV /C so for full scale reading i need to get 5volts for 1.5volt(i.e at 150degree celsius)
so that counts up for the gain of 5/1.5 =3.3333
so for this i m using 10k/3k resistors as shown in figure but the circuit isnt working. what must be the problem.

please help me out
thanks
with best regards
amit
 

Re: scaling for adc

Couple of issues here:
- If you supply this circuit of single +12V you will never have output in the range of 0V (LM324 is not linear al low voltages).
- LM35 requires a load, and the best results you will have if the load is connected between LM35 output and -Vs (see Typical applications: **broken link removed** ) .. and
therefore I think you should supply your circuit from +12/-5V and compensate for DC offset caused by unbalanced supply with A1 amplifier/buffer+10kpot so at 0V on (+) of A2 you will have 0V at output of A4 ..

Good luck ..
 

scaling for adc

Thanks for replying.

You wrote:
"therefore I think you should supply your circuit from +12/-5V and compensate for DC offset caused by unbalanced supply with A1 amplifier/buffer+10kpot so at 0V on (+) of A2 you will have 0V at output of A4 .. "

what changes should i do in circuit for DC offset, i mean on which pin what should i do????

sorry for asking too basics, but i'm poor in analog circuits.

With best regards,
Amit
 

Re: scaling for adc

Pin(11) of LM324 will go to (-5V), bottom of 10k Pot to (-5V) - multiturn pot will be good choice - and 100k resistor between LM35 output and (-5V) .. rest stays unchanged ..
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…