Other Parts Discussed in Thread: ADS1230
Hi,
I am a hardware engineer in Weighing machine Industry. I am making one low cost 40Kg machine having 2gm accuracy based on TI ADS1130 part. In my design ADS1130 is been interfaced with 8 bit micro controller which is serially connected with ADS1130 part. Load cell specification is as below:
LOAD CELL SEPCIFICATION |
||
Rated Capacity |
40 |
Kg |
Excitation Voltage |
5 |
V |
Rated Output |
1.955 |
mV/V |
I am giving 5V to AVCC & 3.3V to DVCC.
According to above data, at Full load capacity of Load cell, I will get max voltage of 9.775V & ADC Count I should get 65599. But I am getting exactly half of it i.e. 32799. At any weight, corresponding output in ADC count I am getting half of what is theoretically expected. I have verified my schematic, component values and board voltages. All are perfect. Then I verified the data output from ADS1130 on CRO & found also that output data is coming exactly half which shows there is no bug at software side, the data itself is coming half to what is expected.
In order to verify my mistake, I checked one of my competitor product that is using the same ADS1130, there I observed a mysterious thing that he has connected DVCC to pin no 4. Pin no 4 in ADS1130 is actually DGND even than he has connected it to DVCC. I did same thing on my board & immediately I started getting correct result. At full load now I am also getting 65599, but it is beyond my imagination how it is working? How an ADS1130 IC started giving me correct result on applying DVCC at 4 pin which is meant for GND. How this pin is correcting its GAIN? I checked there are no errata on this product. Technically can you guide me on this behaviour of ADS1130 part?
Here I am attaching my schematic & the snap shot of CRO showing the data+Clock signal at 32kg weight.3010.ckt.pdf