op-amps, any idea on how to start!!?

[Mark_1]

can anyone help me answering this problem?

 

[crutschow]

You can use op amp configured as an inverting amp with a feedback resistor selected to give the desired 5V change for a sensor temperature change of 100C (100µA change) at the summing junction. Then you add an input resistor of the proper value connected to a negative reference (stable) voltage to give the desired offset so that 0C (273µA) gives 0V output. Then since the inverting amp will go from 0V to minus 5V, you need to add another inverter with a gain of 1 at the output of the first op amp so that the output goes from 0V to plus 5V.

If you don't understand op amps well enough to follow the above suggestion then I suggest you do a Google search and read up on them, particularly inverting op amp circuits and summing junctions.

 

[Mark_1]

Dear crutschow,

thanks for the reply, it really helps!!

 

[MrAl]

can anyone help me answering this problem?

Hello,


Here is a version that should work from a single power supply and require only one op amp section.
Note that the input sensor polarity is reversed with the positive to ground.

Note also R1 comes from Vcc/273ua and R2 comes from VoutMax/100ua.

 

[crutschow]

Hello,


Here is a version that should work from a single power supply and require only one op amp section.
Note that the input sensor polarity is reversed with the positive to ground.

Note also R1 comes from Vcc/273ua and R2 comes from VoutMax/100ua.

You spoiled the fun. How can he learn if you do all the work for him?

 

[MrAl]

You spoiled the fun. How can he learn if you do all the work for him?

Hi there Carl,

It's up to him now to figure out how and why it works. It didnt sound like he was going to get anywhere but yes maybe i did too much work for him, but on the other hand his other post in this forum suggests he's still a bit out in left field I guess we'll have to wait now to find out.