---
title: "Zero drift and sensitivity drift"
subject: "Instrumentation and Measurement"
chapter: 3
key: "semester_4/instrumentation_and_measurement:zero-drift-sensitivity-drift"
source: https://www.bctengineer.com/q/semester_4/instrumentation_and_measurement/zero-drift-sensitivity-drift
site: BCT Engineering
---

# Zero drift and sensitivity drift

Instrumentation and Measurement · Chapter 3: Static Characteristics of Measurement System

- Asked in: year not given, 2+2 marks
- Video: [Drift in Measurement | Static Characteristics | Electrical And Electronics Measurement](https://www.youtube.com/watch?v=r6_T-EiCFHY) — ENGINEERING TUTORIAL
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/instrumentation_and_measurement/zero-drift-sensitivity-drift
- Whole chapter: https://www.bctengineer.com/md/semester_4/instrumentation_and_measurement/chapter-3

## Question

(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 $^\circ$C. The zero drift is 0.2 mV/$^\circ$C and the sensitivity drift is 0.01 mV/bar per $^\circ$C. Find the output when it reads 6 bar at 40 $^\circ$C.

## 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.

## Answer

#### (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/$^\circ$C.
- **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 $^\circ$C.

```text
 Output |      /  <- sensitivity drift (slope change)
        |    //
        |  ///_/  <- zero drift (parallel shift)
        |_/_/
        +---------------- Input
```

#### (b) Numerical
Temperature change $\Delta T = 40 - 20 = 20\ ^\circ$C.

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

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

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

$$
V_o = 30 + 4 + 1.2 = 35.2\ \text{mV}
$$

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

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What does zero drift do to the calibration line?
   A. Changes its slope
   B. Shifts it parallel by a constant amount
   C. Makes it curved
   D. Has no effect at zero input
   Answer: B. The output at zero input changes, so the whole line moves up or down. (Key point: Zero drift)

2. Sensitivity (scale-factor) drift causes an error that
   A. Is constant at all inputs
   B. Grows with input because the slope changes
   C. Occurs only at zero input
   D. Is unaffected by temperature
   Answer: B. The slope changes, so the error is proportional to the input. (Key point: Sensitivity drift)

3. For ΔT = 20 °C and zero drift 0.2 mV/°C, the zero-drift effect is
   A. 0.2 mV
   B. 1.2 mV
   C. 4 mV
   D. 30 mV
   Answer: C. 0.2 × 20 = 4 mV. (Key point: Zero drift value)

4. What is the output at 6 bar and 40 °C?
   A. 30 mV
   B. 34 mV
   C. 35.2 mV
   D. 31.2 mV
   Answer: C. 30 + 4 (zero drift) + (0.01×20)×6 = 1.2 (sensitivity drift) = 35.2 mV. (Key point: Final output)

## Related in Instrumentation and Measurement

- [Calibration line and nonlinearity of transducer](https://www.bctengineer.com/question.md?key=semester_4%2Finstrumentation_and_measurement%3Acalibration-least-squares-nonlinearity) — Instrumentation and Measurement, chapter 3
- [Second-order transducer frequency and step response](https://www.bctengineer.com/question.md?key=semester_4%2Finstrumentation_and_measurement%3Asecond-order-transducer-numerical) — Instrumentation and Measurement, chapter 4
- [Potentiometer transducer and loading error](https://www.bctengineer.com/question.md?key=semester_4%2Finstrumentation_and_measurement%3Apotentiometer-transducer-loading-error) — Instrumentation and Measurement, chapter 5
- [Gauge resistance change and quarter-bridge output](https://www.bctengineer.com/question.md?key=semester_4%2Finstrumentation_and_measurement%3Agauge-resistance-change-quarter-bridge) — Instrumentation and Measurement, chapter 6
- [Models of zero, first and second order systems](https://www.bctengineer.com/question.md?key=semester_4%2Finstrumentation_and_measurement%3Azero-first-second-order-models) — Instrumentation and Measurement, chapter 4
- [Full-bridge cantilever load cell output](https://www.bctengineer.com/question.md?key=semester_4%2Finstrumentation_and_measurement%3Acantilever-full-bridge-output-numerical) — Instrumentation and Measurement, chapter 6

## Related in other subjects

- [Piezoelectric transducer sensitivity and output voltage](https://www.bctengineer.com/question.md?key=semester_4%2Finstrumentation_i%3Apiezoelectric-transducer-output-voltage) — Instrumentation I, chapter 3
- [Tracking, disturbance rejection and pole sensitivity](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Atrack-reject-sensitivity-160) — Control Systems, chapter 3
- [Two-wire 40 Ω line, input and output voltage](https://www.bctengineer.com/question.md?key=semester_3%2Felectromagnetism%3Atwo-wire-40-ohm-line-voltages) — Electromagnetism, chapter 5
- [Disturbance sensitivity and effect of gain](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Aol-cl-disturbance-gain) — Control Systems, chapter 1