AD5940, calibration

Dear ADI Engineer

When we use AD5940 to measure GSR, the auto calibration of low speed rtia is always failed. The output value of calibrated rtia is negative value. So what's the principle of rtia calibration and what's the possible reason that the calibration can't work

Rtia2 , -1048.218018 , 1886.792358

Rtia3 , -1048.218018 , 1886.792358

Rtia4 , -2358.490479, 4245.2833203

Rtia5 ,  -2358.490479, 4245.2833203

Rtia6 ,  -3018.867920, 9433.961914

Rtia7 ,  2264.1508797924.528320

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Thanks