Any resistance in PCB traces will cause a voltage drop between the actual V_BE at the transistor and the measured V_BE at the temperature sensor, which results in a temperature offset. Using three different current level measurements shown in Figure 1-2, a certain amount of series resistance can be canceled out when solving for temperature.

Figure 1-2 ΔV_BE Measurement with Three Currents

Remote temperature sensors are typically calibrated for transistors with an η-factor of 1.008, but transistors may have η-factors that differ from this. If the value is known, an η-factor correction register can be used to correct the error resulting from a deviation of the calibrated η-factor. A combination of offset and η-factor correction settings can correct for both η-factor errors and other system errors that are present. The Remote Temperature Sensor Calibration Tool can calculate the optimal offset and η-factor correction settings for a given data set, and these register settings can be used with devices such as the TMP468, which includes an independent register for each remote input.

The ratio between the emitter and collector current can be expressed as the reciprocal of beta plus 1 and directly affects temperature readings. Thus, transistors with larger betas experience negligible error due to beta variation, while transistors with beta less than 1 can have large temperature measurement errors as beta approaches 1. Remote temperature sensors with beta compensation, such as the TMP431, can correct for these errors, and devices without beta compensation but with offset and η-factor correction registers can also compensate for beta variation.