I have a controller that can scale a single DCV input/output, but I need need to build a box that can scale 3 additional DCV inputs/outputs with independent signals, all the same amount in relation to the output of the single controller channel.

The voltages are not constant, they swing from .1 to 1V rather randomly.
IE:

input--------- controller scale--------- output
#1=.4vDC -----------(+.2v)-----------#1=.6vDC
#2=.9vDC -----------------------------#2=1.0vDC
#3=.45vDC ----------------------------#3=.65vDC
#4=.5vDC -----------------------------#4=.7vDC

input--------- controller scale--------- output
#1=.7vDC ----------(-.2mv)--------#1=.5vDC
#2=.9vDC ---------------------------#2=.7vDC
#3=.2vDC --------------------------#3=.1vDC
#4=.4vDC ---------------------------#4=.4vDC

Input/Output signal will range from .1vDC-1.0vDC, with a voltage clamp @ .1v and 1.0v.

-Can I use the Vout of a differential amplifier between In#1 and Out#1 as the V1in on a summing amplifier for Inputs#2-#4 and then invert the outputs?

IE:

Differential Amplifier-

V1=.4V
V2=.6V
Vout=.2V

Summing Amplifier#1-

V1=.2
V2=.9
Vout=-1.2, invert to +1.2 (step2, how to clamp@1V?)

Summing Amplifier#2-

V1=.2
V2=.45
Vout=-.65, invert to+.65

Summing Amplifier#3-

V1=.2
V2=.5
Vout=-.7, invert to +.7

I'm just learning about OP Amps, I threw together a basic schematic, thought I'm lost as how to figure the correct resistances. I'm looking for a gain of "0", are resistors necessary?

Is there a simpler way to accomplish this?

Thanks in advance,

John

Attached Images

opamp2.jpg (67.0 KB, 17 views)

 

I don't understand what you need, and I suspect no one else does.
This section makes no sense:

For example, you show input #2 with 0.9V input, and two different output values.
I didn't read the rest of your post, because I assumed it was related to the above.

__________________
Ron

 

Read the rest of the post and maybe it will make sense to you.

Ok, I'll break it down for you.

You've got an Oxygen sensor (Input #1) , it creates a voltage through a chemical reaction, this voltage varies between .1V and 1.0V depending on the oxygen content of a gas stream (stream #1).

I've got a "piggyback" that modifies the voltage from this sensor depending on several variables. (Controller scale), and outputs it (Output #1)

This is all fine and dandy, everything works great.

Now, here's the problem:

I also have 3 more oxygen sensors (Input #2, Input #3, Input #4) that are each in their own separate gas stream.

Hence the voltages from all inputs are almost never the same. 4 sensors, 4 locations, 4 different voltages. But they all follow the same "range" of .1V to 1.0V

I need to build a circuit that can take Input #1 and subtract it from Output #1 (using a differential OP Amp?) to get the voltage "difference" .

Follow me?

Now I need to take this "difference" and add it to each of the other sensor values.

Make sense now?

If Input1= .2V and Output1=.2V then the difference is 0, all signals stay the same.

If Input1=.2V and Output1=.5V then the difference is .3V, all signals need to have .3V added to them.

If Input1 = .2V and Output1=.1V then the difference is -.1V, all signals need to have -.1V added to them (in effect they all need to drop in voltage by .1V).

Easier to understand?

John

 

Is the relationship between Input1 and Output1 predetermined?

Or are both Input1, and Output1, inputs to the proposed circuit?

 

Input1, Input2, Input3, Input4, and Output1 are predetermined, I only list I#1 and O#1 because it is necessary to know the difference between I#1 and O#1 in order to "process" the other signals.

 

EDIT: Disregard the schematic in post #1, as the input numbers don't correspond with the text of my post.

 

That makes more sense. The circuit below should work for you.

Attached Images

signal modifier.PNG (18.7 KB, 15 views)

__________________
Ron

 

Thanks I'll give it a shot next weekend...

Once concern though, won't there be issues of "crosstalk" between the lines?

 

Not unless the output impedance of your sources (inputs) is very high. I made all the resistors 100k to hopefully avoid that potential problem.

__________________
Ron

 

The output impedance of the sensors is ~22Mohm. Should I build voltage followers/buffers into the inputs?

 

Do you have a datasheet that we can look at? I am concerned about their ability to provide a current path for the op amp inputs, even with voltage followers.

__________________
Ron

 

Ugh, that's going to take a while. I'll see what I can dig up.

Thanks for all the help so far, I'll keep you posted.

John

 

Where did you get the 22Meg number?

__________________
Ron

 

Not much info out there, I couldn't find any info on the actual sensors I'm using (other than make/model interchange), it looks like most of the sensors are generic with only the plug being different for each application. The only big difference is between EGO/HEGO being a 0-1V signal and UEGO being a 0-5V signal. I'm running HEGOs.


Split Second (distributor of a relabeled OEM HEGO sensor):
http://www.splitsec.com/products/datapdfs/ego1ds.pdf

Bosch LSU UEGO:
http://www.bosch-motorsport.com/pdf/...mbda/LSU42.pdf

National Semiconductor Lambda interface amplifier:
http://www.datasheetarchive.com/pdf/2013578.pdf

 

From a webarchive from a mailing list (that I just realized is about a decade and a half old...)

http://wps.com/LPG/o2sensor.html

EDIT: the resistance is only >1Mohm until the sensor heats up, then is runs ~10Kohm.