ED7124 Excitation issues


In testing a circuit which is an exact copy of  your CN-0376 schematics for RTD, I come across an annoying situation.

Note that in CN-376 Ref1 is used. I use Ref2 and different AIN's see software below.

The excitation current drops to 0 after some time. I could set the time with the delay parameter!

I would expect to see a continuous voltage at the IOUT pin of approx 2.5V @ (Rref +Rrtd+Rbias)= 10K Ohm .

Again, if I remove the delay, the circuit does not work because I don't get any excitation.

What is happening here?

Brg Joost

                SPI.transfer(0x01);                              // internal ref enable = 01 ; ref enble  & CS_EN High : 03
                SPI.transfer(WRITE_OPERATION | IO_CONTROL1);     //Exitation                       
                SPI.transfer(0x00);                              //AIN0 Iout0 enable 250 uA; ; Iout 1 off;                                   
                SPI.transfer(WRITE_OPERATION | CH0);
                SPI.transfer(0x81);                             // 80 = enable
                SPI.transfer(0x6A);                             // AIN11+; AIN10-         
                SPI.transfer(WRITE_OPERATION | CONFIG0);        //Ref2; AIN buf on; Ref buf on; bipolair
                SPI.transfer(0x09);                             // 09E8 =Ref2, all buf's on
                SPI.transfer(0xE8);                             //PGA =1               
                delay (10000);

  • Hi,

    May I clarify what do you mean by drops to 0 after some time? Does it drops upon power up/reset or does it drops anywhere between measurements? May I know also if you are continuously converting or in single conversion mode? The excitation currents are disabled in standby mode and the part always revert to standby mode after every single conversion. The settling time of the excitation current is also dependent on the external RC values connected to the ADC. Can you check if this might be the case?