There are many contributing error factors which go into a total uncertainty calculation and the proportion contributed by each one will be different from one measurement technology to another.
The way accuracy is defined for pressure instruments on technical data sheets can vary significantly across manufacturers and product types.
- 1 Specification Examples
- 2 Glossary
- 2.1 Accuracy
- 2.2 BSL – Best Straight Line
- 2.3 Drift
- 2.4 FRO – Full Range Output
- 2.5 FS – Full Scale / Full Span
- 2.6 FSO – Full Scale Output
- 2.7 Hysteresis
- 2.8 Linearity
- 2.9 Long Term Drift
- 2.10 Long Term Repeatability
- 2.11 Long Term Stability
- 2.12 NLH – Non-Linearity and Hysteresis
- 2.13 NLHR – Non-Linearity, Hysteresis and Repeatability
- 2.14 Non-Linearity
- 2.15 Non-Repeatability
- 2.16 Precision
- 2.17 Range
- 2.18 RDG – Reading
- 2.19 Referred Temperature Error
- 2.20 Repeatability
- 2.21 Resolution
- 2.22 Short Term Repeatability
- 2.23 Span
- 2.24 Span Offset
- 2.25 Span Stability
- 2.26 Span Drift
- 2.27 Stability
- 2.28 TEB (i) – Thermal / Temperature Error Band
- 2.29 TEB (ii) – Total Error Band
- 2.30 TSL – Terminal Straight Line
- 2.31 TSS – Thermal / Temperature Span Sensitivity
- 2.32 TZS – Thermal / Temperature Zero Shift
- 2.33 URL – Upper Range Limit
- 2.34 Zero Drift
- 2.35 Zero Offset
- 2.36 Zero Stability
- 3 Help
Please click on an example term below to be guided to the associated glossary explanation:
Room Temperature Accuracy
- 0.25 % FS NLHR BSL
- 0.5 % FS TSL
- 0.25% FRO
- 0.2% URL
- 0.05% of rdg from 10 to 100% FS
- 0.15% Rdg + 0.15% FS + 1 digit resolution
- 0.02% full span hysteresis
- 0.01% full scale non-repeatability
- 0.025% full span non-linearity
- 0.35% FSO NLH BSL
Zero and Span Setting
- 1% FS TEB, compensated temperature range -20 to +80 degC
- 0.5% FRO RTE @ 23degC, from -10 to +50 degC
- 0.005 % FS / deg C TZS, over -20 to +80 degC
- 0.005 % span / deg C TSS, comp temp range -20 to +80 degC
Total Error Band
How close the measured reading is to a reference point or value.
BSL – Best Straight Line
A virtual line derived from a set of non-linear points which is used to demonstrate the best accuracy that can be achieved from the product.
FRO – Full Range Output
The difference in output signal between the minimum and maximum measurable pressure. Another way of describing the full scale for pressure sensors.
FS – Full Scale / Full Span
The difference between the lowest and highest measured point.
FSO – Full Scale Output
See full range output.
The shift in measurement when comparing between readings of the same pressure which were taken following an increase in pressure and a decrease in pressure.
The straightness of a set of measured points compared to a perfectly straight line.
Long Term Drift
Long Term Repeatability
The amount of change in measured points following many measurement cycles from low to high, then to low again over a long period of time.
Long Term Stability
NLH – Non-Linearity and Hysteresis
An accuracy or precision specification that only considers one cycle of increasing and decreasing pressure and excludes any short term repeatability effects.
NLHR – Non-Linearity, Hysteresis and Repeatability
Defines the limits of variation in measurement, i.e. 100% span
RDG – Reading
Used to distinguish a percentage accuracy which varies proportionally to the measured span (% of reading) from one which is a fixed percentage of the maximum measurement reading (i.e. % of full scale).
Referred Temperature Error
A fixed temperature reference is defined (usually room temperature) which is representative of the average operating temperature. The temperature error is then defined as a +/- value of the largest error.
The amount of change in measured points following a number of measurement cycles from low to high, then to low again over a period of time.
The ability of a device to distinguish a measurement via a reading or an signal output. In most cases the resolution should be much better than the overall accuracy, but in some cases the resolution can become a significant part of the total measurement uncertainty.
Short Term Repeatability
The amount of change in measured points following a few measurement cycles from low to high, then to low again over a short period of time.
The difference between any measured point and the lowest value.
The variation in measured span compared to the perfect span reading, which is either represented as a percentage, pressure unit or output value error.
The amount of long term measurement variation which is only attributed to the span.
See span stability.
The amount of measurement change expected over a long period of time.
TEB (i) – Thermal / Temperature Error Band
The difference between the most negative and positive error across the whole temperature range. The difference is then halved and expressed as a +/- error.
TEB (ii) – Total Error Band
A combined error that includes linearity, hysteresis, repeatability, zero setting, span setting and thermal errors. It may also include stability error if a time factor is included with the total error band.
TSL – Terminal Straight Line
The line created by joining the lowest and highest measured points together. The error of all other measured points is referred to this line
TSS – Thermal / Temperature Span Sensitivity
TZS – Thermal / Temperature Zero Shift
URL – Upper Range Limit
Used to define the accuracy as a factor of the maximum range of a rangeable device rather than an adjusted (turndown) range.
See zero stability.
The amount of variation of the lowest measured reading compared to a perfect reading, which can be expressed as a percentage of full scale (%FS) or measurement units.
The amount of long term measurement variation which only affects the zero offset.
Resolution vs Accuracy
Is Measurement Resolution the same as Accuracy?
You will find mentions of resolution and accuracy on many product information sheets for pressure measuring equipment, however when discussing the performance of equipment the two terms often get confused as meaning the same.
Resolution defines the ability to distinguish one reading from another. For a digital pressure gauge the resolution is normally referred to as the number of readable digits, e.g. 2 bar range with a 5 digit display would have a 0.1 mbar resolution.
A strain gauge pressure sensor without any amplification is described as having a signal output with infinite resolution, since there is no signal conditioning to limit it.
Accuracy refers to the worse case error in measuring a particular reading compared to the actual value. If the resolution is of a similar value to the accuracy it should be included in the accuracy statement, since the true uncertainty of reading should also encompass readability.
The following are examples of how resolution and accuracy are described in specifications of pressure measuring equipment:
Digital Pressure Gauge
Pressure Range: 200 bar
Accuracy: 0.05% Full Scale = 100 mbar
Display Resolution: 5 digits = 10 mbar
Amplified Pressure Transducer (0-10Vdc out)
Pressure Range: 200 bar
Accuracy: 0.25% Full Scale = 500 mbar/25mV
Digital to Analog Amplifier Resolution: 0.002% Full Span = 4 mbar/0.2mV