Long leads to a PRTD can cause offset errors. Using a 4-wire Kelvin arrangement minimizes these. If the µC's A-D has external reference-voltage pins, they can be driven from the circuit for (notionally) improved accuracy

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Other Materials from the Main Document

• Article «Dropping a PRTD into a thermistor slot - impossible?»
• Figure 1. A basic thermistor circuit, together with its calculated response
• Figure 2. Probably the simplest circuit (2a) that can give an output from a PRTD to match a thermistor's response, with a slightly better variant (2b). These are both flawed, and the component values are not optimized. They are to show the principle, not the practi
• Figure 3. The final, workable circuit. Amplification and offsetting are now separate, making calibration much easier
• Figure 4. Plotting the output against the RTD's resistance now gives a result that is almost indistinguishable from the straight-line target, the (idealized) error corresponding to much less than 1 millidegree. This shows the performance limit for this circuit; don
• Figure 5. Long leads to a PRTD can cause offset errors. Using a 4-wire Kelvin arrangement minimizes these. If the µC's A-D has external reference-voltage pins, they can be driven from the circuit for (notionally) improved accuracy