Formula & Calculator
Full-Scale Accuracy
Expresses instrument accuracy relative to its full-scale deflection (FSD) reading.
Interpretation
Full‑scale accuracy = 1 − (|error| / FSD) gives accuracy relative to the full‑scale deflection (maximum reading).
It is often used for meters and transducers.
Example: error=0.5V, FSD=10V → accuracy = 1 − 0.5/10 = 0.95 (or 95%).
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| Accuracy | Accuracy (as a fraction of full scale) | dimensionless |
| error | Absolute error | same units as FSD |
| FSD | Full scale deflection (full range value) | same units as error |
What it means
Full‑scale accuracy is a measure of how close a reading is to the true value, expressed relative to the full‑scale deflection (FSD). Accuracy = 1 − (|error| / FSD). It is often used for analog meters and transducers. For example, a voltmeter with a 10V range and an error of 0.5V has accuracy = 1 − 0.5/10 = 0.95 (or 95%). Full‑scale accuracy is less informative for low readings because the absolute error is constant; a 1% FSD error is much larger as a percentage of a small reading. This is why instruments are often specified in terms of reading plus range. Example: A multimeter with a 20V range and accuracy of ±(0.5% of reading + 2 digits) uses both types of specifications. Understanding full‑scale accuracy helps in interpreting meter specifications.
Worked example
Full‑Scale Accuracy – Practical Example
Real‑World| Parameter | Value |
|---|---|
| Error | 0.1 A |
| FSD | 10 A |
| Formula | Accuracy = 1 − (|error|/FSD) |
Common mistakes
Watch unit consistency and the assumptions behind the formula; misapplying it outside its valid conditions is the most frequent error.Applications
Full‑scale accuracy = 1 − (|error|/FSD) gives accuracy relative to the maximum reading of an instrument. It is used to specify meter accuracy, often expressed as a percentage of full scale. Engineers use it to interpret specifications and to ensure instruments meet requirements. This definition is common in analog meters and transducers.
- Meter specification and interpretation
- Transducer and sensor accuracy characterisation
- Data acquisition system accuracy assessment
- Quality assurance and calibration
- Educational understanding of accuracy definitions
Frequently Asked Questions
Full‑scale accuracy is Accuracy = 1 − (|error| / FSD), where FSD is the full‑scale deflection (maximum reading) of the instrument. It is often expressed as a percentage.
Full‑scale accuracy gives a fixed error (e.g., ±1% of full scale). Reading accuracy gives an error proportional to the reading (e.g., ±1% of reading). For low readings, full‑scale accuracy is worse.
Absolute error = (Accuracy % / 100) × FSD. For example, a ±2% full‑scale accuracy on a 100 V meter gives ±2 V error.
Common errors: 1) confusing full‑scale accuracy with reading accuracy, 2) using the wrong FSD value, 3) applying the accuracy to values near zero incorrectly, 4) forgetting that the error is constant across the scale.
Analog meters have a constant error determined by the movement and scale; it is convenient to specify as a percentage of full scale.
Specifying accuracy of voltmeters, ammeters, and other measurement instruments.
For wide‑range measurements, reading accuracy is better. For narrow‑range near full scale, both are similar. Full‑scale accuracy is common in low‑cost meters.
Temperature changes can affect the meter movement and components, causing additional error. Specifications often include a temperature coefficient.