1. I have application where I need to measure strain (quarter bridge three wire) of 120ohm.
2. This is power sensitive application so I am using small current to excite strain bridge isntaed of voltage.
As I can switch off current source when not required.

3. I am using 24 bit adc - ADS1248 with internal current source.
4. Is there any high precision adc with PGA > 128 ?

 

1. I have application where I need to measure strain (quarter bridge three wire) of 120ohm.
2. This is power sensitive application so I am using small current to excite strain bridge isntaed of voltage.
As I can switch off current source when not required.

3. I am using 24 bit adc - ADS1248 with internal current source.
4. Is there any high precision adc with PGA > 128 ?

As far as I know, no one makes a D-S A/D with gain > 128. And I use these kinds of parts often (most often, ADS1242).

You could drop your Vref to as low as possible (0.5V, I think) or add a high-quality instrumentation amp between the bridge and A/D.

Both solutions will add noise. You can average multiple readings to improve noise performance.

 

1. I have application where I need to measure strain (quarter bridge three wire) of 120ohm.
2. This is power sensitive application so I am using small current to excite strain bridge isntaed of voltage.
As I can switch off current source when not required.

3. I am using 24 bit adc - ADS1248 with internal current source.
4. Is there any high precision adc with PGA > 128 ?

Joey's right... most ADCs have an internal amplifier that works at up to a gain of 8, and after that they implement "digital scaling" which is nothing more than a specially filtered multiplication of the signal obtained from the gain-8 instrumentation amplifier.

 

Joey's right... most ADCs have an internal amplifier that works at up to a gain of 8, and after that they implement "digital scaling" which is nothing more than a specially filtered multiplication of the signal obtained from the gain-8 instrumentation amplifier.

The PGA in a delta sigma is digital, but it's not "faking" the gain. In fact, the input referred noise level drops with increased gain.

I use the ADS1242 with 128 PGA, and it works quite well.

 

The PGA in a delta sigma is digital, but it's not "faking" the gain. In fact, the input referred noise level drops with increased gain.

I use the ADS1242 with 128 PGA, and it works quite well.

I use an old model by Intersil, an HI7190. I found it difficult to program and use... I'm gonna take a look at that ADS1242 of yours, see if it's an improvement... thanks