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Zero drift and sensitivity drift

Short answer

Zero drift is a parallel shift of the calibration line; sensitivity drift is a change in slope. For the transducer, nominal output 30 mV plus 4 mV zero drift plus 1.2 mV from sensitivity drift gives total output 35.2 mV at 6 bar and 40°C.

(a) Explain sensitivity to disturbance, with zero drift and sensitivity drift (scale-factor drift) as the two forms.

(b) A pressure transducer has a sensitivity of 5 mV/bar at 20 ∘^\circC. The zero drift is 0.2 mV/∘^\circC and the sensitivity drift is 0.01 mV/bar per ∘^\circC. Find the output when it reads 6 bar at 40 ∘^\circC.

(a) Sensitivity to disturbance

Environmental inputs such as ambient temperature, supply voltage, vibration or humidity can change the output of an instrument even when the measurand is constant. These are called disturbances (interfering and modifying inputs). Two effects are described.

  • Zero drift (zero shift): the whole calibration line moves up or down by a constant amount, so the output at zero input changes. It is quoted per unit disturbance, e.g. mV/∘^\circC.
  • Sensitivity drift (scale-factor drift): the slope of the calibration line changes, so the error grows with input. Quoted as, e.g., (mV/bar) per ∘^\circC.
 Output |      /  <- sensitivity drift (slope change)
        |    //
        |  ///_/  <- zero drift (parallel shift)
        |_/_/
        +---------------- Input

(b) Numerical

Temperature change ΔT=40−20=20 ∘\Delta T = 40 - 20 = 20\ ^\circC.

Nominal output =5×6=30= 5 \times 6 = 30 mV.

Zero drift =0.2×20=4= 0.2 \times 20 = 4 mV.

Sensitivity drift effect =(0.01×20)×6=1.2= (0.01\times 20)\times 6 = 1.2 mV.

Vo=30+4+1.2=35.2 mVV_o = 30 + 4 + 1.2 = 35.2\ \text{mV}

Answer: output =35.2= 35.2 mV, an error of +5.2+5.2 mV (17%) due to temperature.

✓ Answer checked by Claude Opus 5.5 (high effort)

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