How to measure negative voltage with a ADS8887 ADC?

[orionsbelt]

Hi guys

I have an ADS8887 (18 bit) which will read data from an accelerometer. The accelerometer measures acceleration with a full scale range of -3g to +3g and the sensitivity is 1.2V/g. It has a POS and NEG output.

The signal from the accelerometer is amplified about 1000 times (which is needed for this particular project) using INA163. The output of INA163 is then connected to AINP of ADS8887. I have connected AINN to the ground since that pin is not being used, because INA163 has built in differential amplifier.

For the Reference voltage to the ADC, I am using a REF5020, providing 2.048V.

Now, my question is whether I would be able to measure the negative voltage from the accelerometer?

Or should I use different ADC and Voltage reference? Any suggestion?

Regards
OB

 

[Audioguru]

Your negative voltage has two wires, a negative output and a common output sometimes called "ground". If the circuits are not earthed then if you simply swap the wires then the negative wire can be the common input to the ADC and the common wire can be a positive voltage input to the ADC.

 

[Vbase]

Connect 1K from your ref to the ADC input and another 1K from ADC input to your signal. When your signal is +1.024V you get max output from the ADC and when your signal is -1.024V your output is zero.
You can use more than 1K if your ADC tolerates it.

 

[KlausST]

Hi,

a schematic could help to show what you needs.

Do you need positive AND negative signals?
Do you have dual power supply?

***
Maybe what you need is to pull INA´s "REF" (pin 10) to (ADC_input_range / 2). Often this is VRef/2.

Klaus