Hello Mr.BOB. Thank you for your support. I have one more query
I connected 4-20mA input from my mA source to the input (terminal T1 terminal no 2 and 3) of my circuit as shown in circuit diagram attached(Please visit the site to view this file) and turn SW1 on so that voltage across resistor R9 is given to ADS1148 input. I have found that I am getting non linear ADC result for different mA levels in 4 – 20mA range. 4 – 20mA is converted to mV by the resistor R9 = 51E as shown in the attached diagram. I also shorted the series resistors R11 and R12.
The ADC codes obtained are as follows formV input given to ADS1147:
185mV ADC result = 16B9
372mV ADC result = 2F2C
560mV ADC result = 4961
750mV ADC result = 6615
The ADC result for thermocouple input for the same configuration as mentioned in my previous mail was found to be OK. For 4-20mA input the configuration is as follows:
1) MUX selection for channel 1(MUX0 = 0x01) or
2) VBias selection for channel 1(Vbias = 0x02)
3) MUX1 selection for reference(MUX1 = 0x30) i.e. internal reference ON and onboard reference selected.
4) SYS0 selection for PGA(SYS0 = 0x60) i.e.PGA gain set for 32
5) IDAC0 = 0x00 and IDAC0 = 0xff as no current source is selected.
Please suggest where I am wrong.
Regards,
Dhiren
