Which stages in a HART device can be adjusted during the calibration process?

• A. Stage 1 only
• B. Stages 1 and 3 only
• C. Stages 2 and 4
• D. All stages

Answer: (B)

In calibrating a HART transmitter, you’re adjusting the parts of the signal path that define the basic relationship between the measured process variable and the output current. The most important adjustments are the zero and the span—often referred to as the baseline (where the output starts at the low end) and the gain (how much the output changes per unit of input). These two adjustments determine how the device maps the input range to the 4–20 mA output, so they are the ones you tweak during calibration. The other stages are typically related to internal references, diagnostics, or digital communication setup and are not adjusted in a standard field calibration. Therefore, only the first and third stages are adjusted during calibration.