circuit design

[Lahari]

I have to design a circuit using a temperature sensor(LM35) and an amplifier. Supply voltage is taking by a 12V, 10mA supply. I am using a zener voltage regulator across the supply to stable the voltage. It is giving 5V. So, my supply to sensor is 5V. The output of the sensor is now amplified by a LM324 and from the amplifier, I will take the output. I have given input and feedback resistance to set the gain of the amplifier. Besides these, what I have to connect to complete this circuit by removing noise, ac signal and other hazards? and how I compensate the variable temperature effect?My circuit image is attached herewith. please help...

 

[ericgibbs]

I have to design a circuit using a temperature sensor(LM35) and an amplifier. Supply voltage is taking by a 12V, 10mA supply. I am using a zener voltage regulator across the supply to stable the voltage. It is giving 5V. So, my supply to sensor is 5V. The output of the sensor is now amplified by a LM324 and from the amplifier, I will take the output. I have given input and feedback resistance to set the gain of the amplifier. Besides these, what I have to connect to complete this circuit by removing noise, ac signal and other hazards? and how I compensate the variable temperature effect?My circuit image is attached herewith. please help...

hi,
Because you are using single supply voltage of 5V and a LM324 OPA.
The maximum output from the LM324 will be limited to 3.5V.

I would suggest a 7.5Volt Zener diode [ or 9V], the LM35 will work OK at those voltages.
Also you do not want to invert the LM35 signal so use the LM324 non inverting input for the LM35 output.

You have not stated the range of temperatures you want to measure, the standard LM35 circuit will work from +2C thru +150C, outputting 10mV/C

Do you follow OK.?

 

[Lahari]

Thank you for your reply. Actually I want to use 5 to 6v zener diode as these zener diodes affects less by temperature. so I want to change the opamp. Most probably MCP6004 gives output as 4.7v for 5v input. is it true? will it work?
Yes, I should connect the input into the non inverting terminal. I have tested the circuit in breadboard.
My temperature range is 4 to 40 degree C.
The other thing I want to know is, where and what value of capacitance and resistance have to add with this circuit for dc coupling, and to remove noise and other hazards to make it in PCB? I want to make it a complete circuit. please help..

 

[ericgibbs]

Thank you for your reply. Actually I want to use 5 to 6v zener diode as these zener diodes affects less by temperature. so I want to change the opamp. Most probably MCP6004 gives output as 4.7v for 5v input. is it true? will it work?
Yes, I should connect the input into the non inverting terminal. I have tested the circuit in breadboard.
My temperature range is 4 to 40 degree C.
The other thing I want to know is, where and what value of capacitance and resistance have to add with this circuit for dc coupling, and to remove noise and other hazards to make it in PCB? I want to make it a complete circuit. please help..

hi,
For decoupling use a 100nF and a 22uF capacitor across the +5V [zener output], also have decoupling on the supply thats driving the resistor/zener.

With a 5V supply the MCP will swing to within 25mV of the supply values,
so thats 4.97V and 0.025V.... dont use a low value load resistor on the output of the MCP...

It is correct that zeners around 5V thru 6v2 do have a flat-ish tempr versus V curve.

 

[Lahari]

what is the problem of using low value load resistor at the output of the MCP? what the range of resistor should be? I shall use a data acquisition card at the end.

 

[ericgibbs]

what is the problem of using low value load resistor at the output of the MCP? what the range of resistor should be? I shall use a data acquisition card at the end.

What is the output of the MCP connected into.??

 

[Lahari]

the output of MCP will be connected into a data acquisition card.

 

[ericgibbs]

the output of MCP will be connected into a data acquisition card.

I would say that will be OK.

 

[Reloadron]

If you look at this data sheet for the LM35 and note the design (circuit) shown in Figure 9 it may offer you a good solution. Granted not quite what you have been working but may be a good approach. 4 to 20 mA is 0 to 100 C which could be easily 2 to 10 volts or 1 to 5 volts = 0 to 100 degrees C. That method should work well with a DAQ card.

Just a possible suggestion....

<EDIT> Morning Eric. Up and about. </EDIT>

Ron

 

[Lahari]

it is working with DAQ card but the output has a swing of +/- 0.2. why it is happening? should I add any filter to remove any noise?

 

[ericgibbs]

it is working with DAQ card but the output has a swing of +/- 0.2. why it is happening? should I add any filter to remove any noise?

Post details of DAQ input circuit, it may be expecting a current loop input.??????

OT: Morning Ron, hope the OP can post the DAQ info.

 

[Lahari]

No no, I am confirm that this DAQ card takes input from 0-5V.

 

[ericgibbs]

No no, I am confirm that this DAQ card takes input from 0-5V.

Ok, for some reason the DAQ input is pulling the output of the OPA low.?

Get a 5V supply and a 1K resistor, connect the 5V and the 1K is series with a amp meter, set to mA current and measure how much current flows into the DAQ pin.
The 0V side of the 5V will be connected to the 0V of the DAQ, lets know what you measure.

EDIT:
Also post a circuit diagram with pin numbers and component values.