What type of error might be indicated if a gauge reads 14.9 psi at 15 psi and 15.2 psig at a pressure reduced back to 15 psi?

The situation described involves a gauge that shows different readings at the same pressure point when the pressure is increased and then decreased. This behavior is indicative of hysteresis error, which occurs when the output of a sensor or instrument depends not only on its current input but also on its previous history.

In this case, the gauge's reading of 14.9 psi when rising to 15 psi and 15.2 psig when returning to 15 psi suggests that the gauge has a non-linear response based on its path of travel. Hysteresis typically occurs due to mechanical friction or other physical constraints present in the sensing element of the gauge that cause it to 'stick' at certain points.

Unlike span or zero shift errors, which would affect the calibration parameters consistently regardless of the direction of pressure change, hysteresis specifically indicates discrepancies in the readings depending on whether the pressure is being increased or decreased. This makes it clear that the gauge’s output is not consistent when crossing the same reference point on different paths, confirming the presence of hysteresis error.