Analog signal conditioning

[Enrico]

Hi to all...

I'm having troubles while triyng to find a way to convert a signal to
another...

Explaination:

I have 2 devices with 2 different acquisition systems (both automotive ecu).
I need to let both share a NTC temperature sensor.

The first acquisition system use a strange (but nice) way to condition the
signal...

It uses 2 bias resistors, and switch them at a certain temperature for gain
accuracy, giving us a signal like this:

http://www.interwld.com/images/pico/efi2_1-6.png

This is a warmup sample.

I need to not touch or modify this system...

I've computed that the first bias resistor (low temperature) is 3,9k, and
the second is 350ohm.

The second system want a linear response from the NTC, and use a normal
partition resistor conditioning scheme. A bias resistor to +5, the other
lead of the bias to acquisition and with a terminal of the NTC, and the
other lead of the NTC is at ground.

On the second system i can disable the bias resistor, and let it to acquire
the pure signal conditioned by the first system, but the signal is not
suitable...

This evening i try to find a point on the original system where i have a
0-5v signal, for know when there is the bias resistor swap...

I'm sure that it's possible to done it using only analogic devices, without
using uController, ADC and DAC...

Anyone has an advice on how to slove this problem?

Thanks for any help...

 

[Dan H]

Hi to all...

I'm having troubles while triyng to find a way to convert a signal to
another...

Explaination:

I have 2 devices with 2 different acquisition systems (both automotive ecu).
I need to let both share a NTC temperature sensor.

The first acquisition system use a strange (but nice) way to condition the
signal...

It uses 2 bias resistors, and switch them at a certain temperature for gain
accuracy, giving us a signal like this:

http://www.interwld.com/images/pico/efi2_1-6.png

This is a warmup sample.

I need to not touch or modify this system...

I've computed that the first bias resistor (low temperature) is 3,9k, and
the second is 350ohm.

The second system want a linear response from the NTC, and use a normal
partition resistor conditioning scheme. A bias resistor to +5, the other
lead of the bias to acquisition and with a terminal of the NTC, and the
other lead of the NTC is at ground.

On the second system i can disable the bias resistor, and let it to acquire
the pure signal conditioned by the first system, but the signal is not
suitable...

This evening i try to find a point on the original system where i have a
0-5v signal, for know when there is the bias resistor swap...

I'm sure that it's possible to done it using only analogic devices, without
using uController, ADC and DAC...

Anyone has an advice on how to slove this problem?

Thanks for any help...

Try to connect two systems to single temperature sensor will almost
never work especially when the method of measurement is a different as
the ones you have.

You need to have a single device measureing the sensor and feeding a
conditioned signal to the other system

dan

 

[Jamie]

Hi to all...

I'm having troubles while triyng to find a way to convert a signal to
another...

Explaination:

I have 2 devices with 2 different acquisition systems (both automotive ecu).
I need to let both share a NTC temperature sensor.

The first acquisition system use a strange (but nice) way to condition the
signal...

It uses 2 bias resistors, and switch them at a certain temperature for gain
accuracy, giving us a signal like this:

http://www.interwld.com/images/pico/efi2_1-6.png

This is a warmup sample.

I need to not touch or modify this system...

I've computed that the first bias resistor (low temperature) is 3,9k, and
the second is 350ohm.

The second system want a linear response from the NTC, and use a normal
partition resistor conditioning scheme. A bias resistor to +5, the other
lead of the bias to acquisition and with a terminal of the NTC, and the
other lead of the NTC is at ground.

On the second system i can disable the bias resistor, and let it to acquire
the pure signal conditioned by the first system, but the signal is not
suitable...

This evening i try to find a point on the original system where i have a
0-5v signal, for know when there is the bias resistor swap...

I'm sure that it's possible to done it using only analogic devices, without
using uController, ADC and DAC...

Anyone has an advice on how to slove this problem?

Thanks for any help...

that's a simple matter.
use the linear signal to generate the ramp signal you have there.
i think what your looking for is a linear and a switch level signal.
set the NTC circuit to generate the linear signal.
use 2 buffers to isolate the effects from external loads! something
like 2 op-amps using the + input of each connected to the NTC network
a loop back from the output of each op-amp back to the - input of the
op-amp..
so we have the + input of both op-amps connected to gather to the NTC
network for the linear tracking.
the - input of each op-amp is connected to its own output.
now you have 2 op-amps giving you isolated signals that you can
deal with.
use one as is for your linear tracking. and on the other op-amp
you can actually place a voltage divider on the - input instead of the
loop back to get a voltage comparator.
ect..
something to think about.

 

[Enrico]

Nice idea!!!

I'll try to get some schematic in the week end...

Really thanks for the help!