Hi
This time i have another problem. I have to extend range of my RTD transducer to 850'C. Problem is 3 C degree error at the end of range (850'C) at -200 everything is ok.There is some parameters of my design Rbias = 825 Idac 1.5mA Rcomp=220 5SMPS. I dont know where problem lies software or hardware. At first i thought it is gain error but gain error is to low. ill apreciate any question or suggestion.
| AVSS | 0 | Rpt100 | 400 | |||||||||
| AVDD | 5 | Rcomp | 220 | |||||||||
| PGAGAIN | 8 | Ref | 825 | |||||||||
| VinDiff | 0.27 | Idac | 1.50E-003 | |||||||||
| Vref | 2.475 | |||||||||||
| V+ | 3.075 | |||||||||||
| V- | 2.805 | |||||||||||
| Vcm | 1.176 | |||||||||||
| Common mode voltage Range | ||||||||||||
| 1.18 | <Vcm< | 3.82 | ||||||||||
| Full Scale Voltage | ||||||||||||
| FSV | 0.309375 | Temp C | RTD Res | Vref | Vinp | Vinn | Vdiff | VCM | VCM(max) | VCM(MIN) | ||
| Expected differential voltage | 850 | 390.48 | 2.475 | 3.06072 | 2.805 | 0.25572 | 2.93286 | 3.87712 | 1.12288 | |||
| should not exceed the full scale voltage | 600 | 313.71 | 2.475 | 2.945565 | 2.805 | 0.140565 | 2.8752825 | 4.33774 | 0.66226 | |||
| 500 | 290.98 | 2.475 | 2.91147 | 2.805 | 0.10647 | 2.858235 | 4.47412 | 0.52588 | ||||
| 325 | 220.92 | 2.475 | 2.80638 | 2.805 | 0.00138 | 2.80569 | 4.89448 | 0.10552 | ||||
| -200 | 18.52 | 2.475 | 2.50278 | 2.805 | -0.30222 | 2.65389 | 6.10888 | -1.10888 | ||||
| Offset Error | 1.50E-005 | |||||||||||
| GainError at 850"C | 0.000012786 | 0.255*0.05% | ||||||||||
| INL Error | 4.640625E-006 | |||||||||||
| Total Accuracy error | 2.02488813614635E-005 | |||||||||||
| V/'C= | 5.31E-004 | |||||||||||