ZHCSV99C February 1997 – October 2024 XTR105
PRODUCTION DATA
RTD temperature sensors are inherently (but predictably) nonlinear. With the addition of one or two external resistors, RLIN1 and RLIN2, compensation is possible for most of this nonlinearity by using the VLIN linearity correction feature of the XTR105. This results in a 40:1 improvement in linearity over the uncompensated output.
See Figure 7-1 for a typical 2-wire RTD application with linearization. Resistor RLIN1 provides positive feedback and controls linearity correction. RLIN1 is chosen according to the desired temperature range. An equation is given in Figure 7-1.
In 3-wire RTD connections, an additional resistor, RLIN2, is required. As with the 2-wire RTD application, RLIN1 provides positive feedback for linearization. RLIN2 provides an offset canceling current to compensate for wiring resistance encountered in remotely located RTDs. RLIN1 and RLIN2 are chosen such that the currents are equal. This makes the voltage drop in the wiring resistance to the RTD a common-mode signal that is rejected by the XTR105. The nearest standard 1% resistor values for RLIN1 and RLIN2 are adequate for most applications. Table 7-1 provides the 1% resistor values for a 3-wire Pt100 RTD connection.
If no linearity correction is desired, leave the VLIN pin open. With no linearization, RG = 2500m × VFS, where VFS = full-scale input range.