need simple low gain amp

[Dan Major]

I've got two applications using the Dataq DI-194/DI-154 serial port data
loggers. The first application is a gas chromatograph which has a 0-1v dc
output. The second ap is a load cell hooked up to a Maxim instrumentation
amp which will probably have a +/- 3.5v output. The problem is that the
Dataq loggers have a +/- 10 v input with no provision for input scaling. I
need simple 10X and 3X amps to boost the signal so I get better resolution.
I was wondering if a simple LM386 would work for the GC signal (10X gain).
If not, what would be a good amp? Additionally, with the load cell amp,
I'd like to add a high-pass filter to remove some noise generated by
mechanical vibration. Any ideas welcome.

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[mike]

Dan Major wrote:

I've got two applications using the Dataq DI-194/DI-154 serial port data
loggers. The first application is a gas chromatograph which has a 0-1v dc
output. The second ap is a load cell hooked up to a Maxim instrumentation
amp which will probably have a +/- 3.5v output. The problem is that the
Dataq loggers have a +/- 10 v input with no provision for input scaling. I
need simple 10X and 3X amps to boost the signal so I get better resolution.
I was wondering if a simple LM386 would work for the GC signal (10X gain).
If not, what would be a good amp? Additionally, with the load cell amp,
I'd like to add a high-pass filter to remove some noise generated by
mechanical vibration. Any ideas welcome.

If you want better accuracy to go with that better resolution, you need
to pay attention to gain accuracy and offset. LM386 is probably NOT
what you want. I can't give you a number cause I don't know the
resolution of the loggers. Can't tell from your post what the signal
looks like, but high-pass just doesn't seem right.
mike

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[Rolavine]

Subject: need simple low gain amp
From: Dan Major nospam@this.address
Date: 4/28/2004 12:51 AM Pacific Daylight Time
Message-id: <Xns94D91CD0E49BAsoonerboomergbronlin@68.12.19.6

I've got two applications using the Dataq DI-194/DI-154 serial port data
loggers. The first application is a gas chromatograph which has a 0-1v dc
output. The second ap is a load cell hooked up to a Maxim instrumentation
amp which will probably have a +/- 3.5v output. The problem is that the
Dataq loggers have a +/- 10 v input with no provision for input scaling. I
need simple 10X and 3X amps to boost the signal so I get better resolution.
I was wondering if a simple LM386 would work for the GC signal (10X gain).
If not, what would be a good amp? Additionally, with the load cell amp,
I'd like to add a high-pass filter to remove some noise generated by
mechanical vibration. Any ideas welcome.

Presuming you willing to give up half the reading that represents - input

voltages on the 10 gain circuit to the dataq!

For the ten gain you might want to look at a Burr Brown INA106, differential
amplifier. This will give you the ability to subtract common mode noise via the
sensor ground connection. It sounds like your only doing a few of these so
might as well go for the bullet proof solution. This amp has a fixed gain of
ten (very accurate) you won't even need any resistors. Since this is an A to D
system, why not do filtering by averaging readings before reacting?

For your 3 gain amp you could use this same amp with a 3 resistor voltage
divider on the signal. This would simplify the number of parts you need.

In order to use these amps you will need something like a +/- 12 to 15 volt
power supply.


Rocky

 

[Dan Major]

mike <spamme0@juno.com> wrote in news:408F698B.7040700@juno.com:

Dan Major wrote:
I've got two applications using the Dataq DI-194/DI-154 serial port
data loggers. The first application is a gas chromatograph which has
a 0-1v dc output. The second ap is a load cell hooked up to a Maxim
instrumentation amp which will probably have a +/- 3.5v output. The
problem is that the Dataq loggers have a +/- 10 v input with no
provision for input scaling. I need simple 10X and 3X amps to boost
the signal so I get better resolution. I was wondering if a simple
LM386 would work for the GC signal (10X gain). If not, what would be
a good amp? Additionally, with the load cell amp, I'd like to add a
high-pass filter to remove some noise generated by mechanical
vibration. Any ideas welcome.


If you want better accuracy to go with that better resolution, you
need to pay attention to gain accuracy and offset. LM386 is probably
NOT what you want. I can't give you a number cause I don't know the
resolution of the loggers. Can't tell from your post what the signal
looks like, but high-pass just doesn't seem right.
mike

The loggers are +/- 10 v input with 10 and 12 bits resolution. With the
GC I'm stuck with a 0-1 v output. The load cell amp I haven't decided on
yet, but I'm looking at a Maxim amp that outputs about +/- 3 to 3.5 v.
You're right, I meant low-pass to get rid of noise. Averaging the sample
by running average or boxcar averaging might give the filtering I need,
I'll have to look at the frequency response generated.

--
Sooner dot boomer at gbronline dot com

 

[Dan Major]

rolavine@aol.com (Rolavine) wrote in
news:20040428051813.21319.00000397@mb-m04.aol.com:

Subject: need simple low gain amp
From: Dan Major nospam@this.address
Date: 4/28/2004 12:51 AM Pacific Daylight Time
Message-id: <Xns94D91CD0E49BAsoonerboomergbronlin@68.12.19.6

I've got two applications using the Dataq DI-194/DI-154 serial port
data loggers. The first application is a gas chromatograph which has
a 0-1v dc output. The second ap is a load cell hooked up to a Maxim
instrumentation amp which will probably have a +/- 3.5v output. The
problem is that the Dataq loggers have a +/- 10 v input with no
provision for input scaling. I need simple 10X and 3X amps to boost
the signal so I get better resolution. I was wondering if a simple
LM386 would work for the GC signal (10X gain). If not, what would be
a good amp? Additionally, with the load cell amp, I'd like to add a
high-pass filter to remove some noise generated by mechanical
vibration. Any ideas welcome.

Presuming you willing to give up half the reading that represents -
input voltages on the 10 gain circuit to the dataq!

For the ten gain you might want to look at a Burr Brown INA106,
differential amplifier. This will give you the ability to subtract
common mode noise via the sensor ground connection. It sounds like
your only doing a few of these so might as well go for the bullet
proof solution. This amp has a fixed gain of ten (very accurate) you
won't even need any resistors. Since this is an A to D system, why not
do filtering by averaging readings before reacting?

For your 3 gain amp you could use this same amp with a 3 resistor
voltage divider on the signal. This would simplify the number of parts
you need.

In order to use these amps you will need something like a +/- 12 to 15
volt power supply.

I'll look into this amp. It has to be an easily available part (free

samples would be best!). Running averaging or boxcar averaging might give
me the filtering I need. I hadn't thought of that, and it's a good
solution because it doeasn't require any additional hardware and can be
easily adjusted. BTW - I meant *low* pass filter to get rid of noise,
but I guess you understood that.



--
Sooner dot boomer at gbronline dot com