Read the percentage together with its reference
A percentage in a pressure instrument quotation needs a reference quantity. Manufacturers may express a specification as a percentage of span, a percentage of reading or a piecewise expression with additional terms. WIKA's CT 25.10 datasheet demonstrates that different bases can appear even within one product family. Use the definition in the actual datasheet; do not assume every abbreviation FS has the same meaning.
Convert a span-based limit into pressure units
When the manufacturer explicitly defines span as upper endpoint minus lower endpoint, a stated limit of ±a % of span becomes ±(a / 100 × span) in pressure units. For a compound range, include both endpoints in that subtraction. Compare instruments at the pressures that matter to your process rather than comparing only the percentage printed in a brochure.
Work through a hypothetical example
Consider an illustrative 0–100 bar gauge with a stated error limit of ±0.1% of span. Its span is 100 bar, so the limit is ±0.1 bar. At a 10 bar reading, that equals 1% of the reading; at 50 bar, it equals 0.2%. A different illustrative specification of ±0.1% of reading gives ±0.01 bar at 10 bar and ±0.05 bar at 50 bar, if no floor or other term applies. These figures are arithmetic examples, not WESIVO 880 specifications, calibration results or uncertainty values.
Check the complete expression near zero
A pure percentage-of-reading calculation reaches zero at zero pressure. That mathematical result is not proof of a physically perfect zero. Check whether the supplier adds a span term, a minimum error floor, counts, temperature conditions or a lower boundary for the reading-based region. Ask for the permitted error in pressure units at your lowest required point, and retain the supplier's full expression in the purchasing record.
Keep display resolution separate
Resolution concerns the smallest detectable indication change; it does not state how close that indication is to a reference. In a separate hypothetical example, a display step of 0.01 bar can coexist with an error limit of ±0.1 bar. More displayed digits do not by themselves prove a better pressure result. Confirm the displayed step in your selected unit and range rather than inferring it from the number of LCD digits.
Distinguish an error limit from measurement uncertainty
A maximum permissible error is a specification limit; measurement uncertainty describes the dispersion associated with a reported measurement. They answer different questions. When choosing a reference gauge, request relevant calibration results and uncertainty for the intended points and conditions. Do not replace this information with display resolution, a pump's adjustment step or a single accuracy-class number. Apply the laboratory or site's approved method when evaluating the complete comparison setup.
Ask the right questions about WESIVO 880
Published 880 information lists accuracy classes 0.02, 0.05, 0.1 and 0.2 subject to pressure type and range. It also lists a five-digit LCD. This article does not assign an unconfirmed % of span or % of reading definition to those classes. Send the exact pressure type, range and working points, and request written confirmation of the specification basis, environmental conditions and required calibration documentation. Select the configuration from the original range tables rather than applying the best listed class to every model.
百分比必须与基准一起阅读
压力仪表报价中的百分比，需要说明相对于什么量。制造商可能采用量程百分比、读数百分比，或带有附加项的分段表达式。WIKA CT 25.10 产品资料显示，同一产品系列也可能使用不同基准。应按实际产品资料中的定义判断，不能假设所有 FS 缩写都表示同一个量。
将量程百分比换算为压力单位
如果制造商明确将量程跨度定义为上限减下限，则 ±a% 量程跨度对应的误差限为 ±(a / 100 × 跨度)，单位与压力相同。复合量程计算时应同时考虑上下端点。比较仪表时，应关注工艺实际使用的压力点，而不只是比较宣传资料上的百分比。
一个明确标注的通用算例
假设某块 0–100 bar 压力表的误差限为 ±0.1% 量程跨度，跨度为 100 bar，换算后为 ±0.1 bar。在 10 bar 读数时，相当于读数的 1%；在 50 bar 时，相当于 0.2%。另一种假设规格为 ±0.1% 读数，且没有最低误差项或其他附加项，那么在 10 bar 时对应 ±0.01 bar，在 50 bar 时对应 ±0.05 bar。以上仅为数学示例，不是 WESIVO 880 参数、校准结果或不确定度。
接近零点时检查完整表达式
单纯按读数百分比计算，在零压力处会得到零。这一数学结果不能证明仪表零点没有误差。应检查是否另有量程项、最低误差限、字数项、温度条件，或读数百分比适用区间的下边界。向供应商确认最低工作点对应的压力单位误差限，并将完整表达式保留在采购记录中。
显示分辨力要单独看
分辨力涉及能够辨别的最小示值变化，并不说明示值与参考值接近到什么程度。另一个假设例子中，显示步进为 0.01 bar 的仪表，仍可能具有 ±0.1 bar 的误差限。显示位数增加，不能单独证明测量结果更好。应确认所选单位、量程对应的显示步进，不能仅凭液晶位数推断。
误差限与测量不确定度是两种信息
最大允许误差是规格给定的限值；测量不确定度描述与报告测量值相关的分散程度，两者回答的问题不同。选择参考压力表时，应索取对应测量点和条件的校准结果及不确定度。不能用显示分辨力、压力泵调节步进或一个准确度等级数字代替这些信息。完整比较装置的评价应按实验室或现场批准的方法进行。
WESIVO 880 选型应问什么
已发布的 880 信息列有 0.02、0.05、0.1、0.2 准确度等级，具体取决于压力类型和量程，同时列明五位液晶显示。本文不为这些等级擅自指定未经确认的量程百分比或读数百分比定义。请提供准确的压力类型、量程及工作点，书面确认规格基准、环境条件和所需校准文件。按原版量程表选择配置，不能把最高等级套用于所有型号。
Discuss your application
Send your medium, operating conditions, connection, output, quantity and destination. WESIVO will review the configuration before quotation.