In a transmitter, what do zero and span adjustments calibrate?

• A. Zero sets the output at the lower range; span sets the output at the upper range
• B. They adjust display brightness
• C. They set the measurement units
• D. They calibrate temperature compensation

Answer: (A)

The concept being tested is how a transmitter maps the measured quantity to its output signal by establishing a starting point and the size of the range. Zero adjustment sets the output when the input is at the minimum (often zero or the lowest end of the measurement). Span adjustment sets how much the output changes as the input goes from minimum to maximum, effectively setting the upper end of the output range. In a typical 4–20 mA transmitter, zero ensures the minimum input produces the baseline current (often 4 mA), while span makes the full-scale input correspond to the full-scale current (often 20 mA). Together, they define the linear relationship between input and output. The other options don’t describe this mapping of input to output range.