A pressure sensor rated ±0.5% FS does not necessarily limit error to 0.5% of the pressure you are measuring. Its percentage is applied to a fixed full-scale reference, so the allowable error in bar or psi stays constant across the stated measuring range. A ±0.5% of reading specification instead applies the percentage to each indicated pressure, so its calculated error changes with the reading. To compare two devices, convert both specifications into pressure units at your lowest, normal, and highest important operating points.
For example, on a 0–10 bar sensor, ±0.5% FS corresponds to ±0.05 bar. At a 1 bar operating point, that is 5% of the reading. A hypothetical ±0.5% of reading limit at 1 bar would be ±0.005 bar—ten times smaller. These are specification calculations, not test results or a claim that every sensor can achieve the ideal reading-based limit near zero.
What do %FS, %reading, and %span mean?
The denominator after the percentage sign determines the result. For a 0–10 bar calibrated range, full scale and span are both 10 bar, so the arithmetic is straightforward:
| Specification wording | Calculation on a 0–10 bar range | Behavior within the valid range |
|---|---|---|
| ±0.5% FS (full scale) | 0.005 × 10 bar = ±0.05 bar | Fixed pressure-unit limit |
| ±0.5% of reading | 0.005 × indicated pressure | Varies with the pressure reading |
| ±0.5% of calibrated span | 0.005 × (10 − 0) bar = ±0.05 bar | Fixed pressure-unit limit |
In general, if a data sheet defines the denominator as a calibrated span, span = upper range value − lower range value. Then absolute error limit = percentage / 100 × span. If the specification is reading based, absolute error limit = percentage / 100 × indicated reading at each point. The result is an allowable error under the data sheet’s stated conditions; it does not tell you the sensor’s actual error in a particular installation.
The distinction between full scale, upper range value, and span becomes important when the lower endpoint is not zero. Do not assume that a bare “%FS” label has the same denominator in every manufacturer’s document. Ask which pressure interval the stated percentage refers to. Fluke Calibration’s guide to pressure specifications treats %FS, %reading, %span, and combined terms separately.
Worked example: ±0.5% FS versus ±0.5% of reading
Consider two hypothetical 0–10 bar instruments. Instrument A has a ±0.5% FS limit; Instrument B has a ±0.5% of reading limit throughout the points being compared. Their headline numbers are identical, but their pressure-unit limits differ away from full scale.
| Indicated pressure | A: ±0.5% FS | A as % of indicated reading | B: ±0.5% of reading |
|---|---|---|---|
| 1 bar | ±0.05 bar | ±5% | ±0.005 bar |
| 5 bar | ±0.05 bar | ±1% | ±0.025 bar |
| 10 bar | ±0.05 bar | ±0.5% | ±0.05 bar |
The first column is an assumed operating point, not a measured observation. At 5 bar, A’s limit is still ±0.05 bar because 0.005 × 10 = 0.05. Expressed relative to the current 5 bar reading, 0.05 / 5 × 100 = 1%. B’s hypothetical limit is 0.005 × 5 = 0.025 bar at the same point. The two mathematical limits meet at 10 bar.
This difference matters when a controller switches a pump at 1 bar, a process normally runs at 5 bar, or a low-pressure alarm has a tight deadband. A percentage figure that looks small on a product page may consume most of the allowed error at the operating point. Set the permitted error in pressure units first, then check the data sheet.
A quick formula for the low end
For a zero-based range, the percent-of-reading equivalent of a fixed %FS limit at a nonzero pressure is:
equivalent % of reading = stated %FS × full-scale pressure / indicated pressure。
Thus, a ±0.5% FS specification at 10% of a 0–10 bar range equates to ±5% of that 1 bar reading. This conversion is for comparing error magnitudes, 不是 a reclassification of the device as “5% of reading accuracy.” It is undefined at zero because division by zero is undefined.
Why the selected pressure range changes the answer
Suppose an application normally operates at 6 bar. Two candidate instruments both state ±0.5% FS, but one is calibrated 0–10 bar and the other 0–20 bar. The first gives a headline limit of 0.005 × 10 = ±0.05 bar; the second gives 0.005 × 20 = ±0.10 bar. At 6 bar, these correspond to about ±0.83% and ±1.67% of reading, respectively. The wider range doubles this part of the absolute error allowance.
That does 不是 mean you should always buy the narrowest possible range. Pressure spikes, proof-pressure requirements, startup transients, and uncertainty in the operating envelope can make a narrow choice unsuitable. A calibrated measuring limit and an overload-survival rating answer different questions. Review both before selecting a span; our industrial pressure sensor buying guide covers the broader range and overload decisions.
For a useful comparison, write a three-row worksheet with the minimum important reading，，，， normal reading， 和 maximum important reading. Convert each candidate’s full accuracy expression into bar, kPa, or psi at all three points. If units differ between data sheets, convert them consistently; the pressure units guide provides common unit relationships.
What happens at zero and on a non-zero-based range?
A pure ±0.5% of reading formula evaluates to zero when the reading is zero. Real measurement systems have offset, resolution, reference uncertainty, noise, or a stated lower limit for the reading-based claim. A practical data sheet may therefore specify % of reading plus a fixed floor, or use one expression above a threshold and another below it. Do not extend a reading-based claim below its stated valid range. The Fluke Calibration application note explicitly explains this error-floor issue.
For example, a hypothetical specification of ±(0.2% of reading + 0.05% of a 10 bar span) gives a limit of ±(0.002 × 5 + 0.0005 × 10) = ±0.015 bar at 5 bar. At zero, its fixed term still gives ±0.005 bar. Do not replace the plus sign with “whichever is greater”: those are different specification rules.
A range with a nonzero lower endpoint needs its own denominator check. For a calibrated range of −1 to +9 bar, the span is 9 − (−1) = 10 bar, while the upper endpoint is 9 bar. A stated ±0.5% of span means ±0.05 bar. If a document merely says ±0.5% “FS,” ask whether that means upper endpoint, nominal sensor range, calibrated span, or something else; assigning 10 bar without evidence could misstate the result. Also retain the pressure reference—gauge, absolute, or differential—when defining the range.
What else is inside—or outside—the accuracy number?
Two data sheets can use the same ±0.5% FS headline and still describe different test conditions. Before comparing them, identify the exact definition of accuracy. Does it include 非线性，，，， 滞后现象 (different results when pressure rises and falls), 重复性, zero and span offsets, and temperature effects? Does a linearity figure use a best-fit straight line or a line through specified endpoints? These distinctions affect the allowed deviation. The WIKA pressure handbook describes different conformity methods; the number should always be read with its method and footnotes.
Also separate compensated temperature range 从 working temperature range. A unit may operate over a broad ambient range while its reference accuracy applies at a narrower temperature. Temperature coefficients or drift may need to be considered at the actual process and electronics temperatures. Long-term stability over months or years is a separate concern when a sensor is not recalibrated frequently. The receiving electronics, supply, analog input, wiring, installation, and pressure tap can add further system error.
Do not mechanically add every published percentage. A headline accuracy might already include hysteresis and repeatability, while another data sheet lists these as separate specifications. Some values are worst-case limits; others are typical or statistically combined uncertainties. Request the manufacturer’s total error band or error budget definition for the ordered configuration and the temperature interval that matters to you. The objective is a defensible system tolerance, not the smallest isolated catalog number.
How to compare two pressure sensor data sheets
Use the same application points and the same units for every candidate. A practical comparison record contains:
- Pressure reference and calibrated limits: gauge, absolute, sealed gauge, or differential; lower and upper values; units.
- Exact denominator: %FS, % of calibrated span, % of upper range value, % of reading, or a combined expression.
- Validity conditions: pressure interval, reference temperature, compensated temperature range, supply, and output loading.
- Included error components: linearity method, hysteresis, repeatability, zero and span effects, temperature drift, and time-based stability.
- Absolute error at each decision point: calculate in bar, kPa, or psi at the minimum, normal, and maximum important readings; compare against alarm and control tolerances.
- Verification method: sample test points, pressure standard, rising and falling pressure sequence, temperature points, and acceptance rule.
For an OEM qualification, request the data sheet and drawing for the specific proposed variant, then test samples under the relevant supply, medium, temperature, and output conditions. A calibration certificate at one condition does not automatically prove the installed error budget across the complete duty cycle. If the electronics architecture is still open, our sensor, transducer, and transmitter comparison explains how much conditioning the OEM must provide.
How do the Winsen WPCK07 and WPCK63 specifications fit?
Winsen’s official product pages list ±0.5% FS accuracy for both WPCK07 和 WPCK63. Neither page describes these models as ±0.5% of reading. The 0–10 bar examples above show how to interpret a %FS rating if the ordered range and specification conditions correspond to that example; they are not a measured performance report for either product.
| 模型 | Relevant published information | What to confirm for a fair comparison |
|---|---|---|
| WPCK07 | Diffused-silicon transmitter, ±0.5% FS; official page lists gauge/absolute/sealed-gauge choices and 4–20 mA plus other output options. | Ordered pressure range and output, definition of the ±0.5% FS figure, temperature terms, overload rating, and compatible medium. |
| WPCK63 | Compact diffused-silicon transmitter, ±0.5% FS; official page lists 0.2–2.3 V or I²C outputs and separate analog/digital compensation ranges. | Ordered span, interface, compensation interval, temperature drift, annual stability, process connection, and medium. |
The models address different integration needs. WPCK07 offers field-style output options, while WPCK63 supports compact voltage or digital integration. A shared nominal %FS rating alone does not make their full application error identical. Ask Winsen for the latest data sheet and variant-specific performance conditions before freezing the OEM specification.
常见问题
Is ±0.5% FS the same as ±0.5% of reading?
Only at full scale on a zero-based range in the simple comparison above. At a lower reading, ±0.5% FS remains a fixed pressure-unit limit, while ±0.5% of reading produces a smaller mathematical value if the latter specification is valid there.
Does a %reading specification mean zero error at zero pressure?
No. The bare formula returns zero, but a real instrument needs a stated offset floor, lower valid limit, or a combined specification. Read the complete data-sheet rule.
Is %FS always equal to percent of calibrated span?
Do not assume so. They coincide in the simple 0–10 bar example, but a nonzero lower range value, reranging, or manufacturer-specific use of “FS” can change the denominator. Request its definition.
Which is more useful: accuracy or resolution?
They answer different questions. Resolution describes the smallest output change the system can show; accuracy constrains how far the indicated value may be from the reference under specified conditions. A finely resolved output may still have an offset or temperature error.
Should I compare the 0–10 bar and 0–20 bar options at full scale?
Compare them at the pressures the equipment actually uses, especially alarms and normal control points. Check transients and proof pressure separately so the chosen measuring range survives the duty.
Which calibration points should an OEM check?
Include the minimum, normal, and maximum decision points, plus any alarm threshold with a tight tolerance. Test rising and falling pressure and the temperature conditions that matter to the application. Agree on a reference standard and acceptance rule before sample testing.
Request an application-specific accuracy check
If you are comparing WPCK07, WPCK63, or another pressure sensing option, send Winsen your pressure reference, calibrated range, minimum/normal/maximum operating points, permitted error in pressure units, medium, temperature range, output, and expected annual volume. Ask for the latest variant-specific data sheet and sample-test conditions through the Winsen contact page. That information lets the engineering team discuss a measurable requirement rather than a percentage headline alone.
