High frequency common mode noise injected into the power and communication lines (common in VFD applications) were affecting the RTD readings.
Add .1UF 16V 20% X7R SMT 0603 (PID 150253) capacitor on top of D1 through D6 as shown in the photo. Capacitor connects from the 6 RTD signal lines to analog ground.
This capacitor modification was tested by SPOC Automation at two sites operated by El Paso Exploration and Production. Both 4102 units in the field now have significantly improved VFD induced noise performance on the RTD inputs.
KIT 4299 sensor interface board (308084, 308084A, 308084C) used in 4102 and 4203 SCADASense products.