Humidity measurement and control is called for in a wide variety of industrial applications. Each application has a different set of requirements for humidity instruments, such as required measurement range, tolerance to extreme temperature and pressure conditions, ability to recover from condensation, ability to operate in hazardous environments, and options for installation and calibration. There is no single device that is suitable for all needs. In fact, the range of available equipment is quite large, varying both in cost and quality.

高湿度的正确仪器
Environments with >90%RH are defined here as high humidity environments. At 90%RH a difference of 2°C can cause water to condense on the sensor, which in an unventilated space may take hours to dry. Vaisala humidity sensors will recover from condensation. However, if the condensed water is contaminated, the instrument accuracy can be affected due to deposits on the sensor, especially salt deposits. Even the life of the sensor may be shortened. In applications with high humidity where condensation can occur, a warmed sensor head probe such as theIndigo compatible Vaisala HUMICAP® Humidity and Temperature Probe HMP7或者Vaisalahumicap®Humidity and Temperature Transmitter HMT337应该使用。

The right instrument for low humidity
此处将<10％RH的环境定义为低湿度环境。在低湿度下，测量相对湿度的仪器的校准精度可能不足。相反，测量露点将提供良好的湿度指示。例如，VaisalaDryCap®产品设计用于测量露点。

如果干燥机在压缩空气系统中失败，则可能会出现水冷凝，并且需要恢复仪器。在这种情况下，许多露点传感器被损坏或破坏，但是VaisalaDryCap®露点传感器承受高湿度 - 甚至水峰值。

极端温度和压力条件的正确仪器
持续暴露于极端温度可能会随着时间的推移影响传感器和探测材料。因此，为苛刻的环境选择合适的产品非常重要。在高于60°C的温度下，发射机电子设备应安装在过程之外，并且只能将合适的高温探针插入高温环境中。此外，需要内置的温度补偿以最大程度地减少由于温度波动或极端温度下的操作而造成的错误。

当测量在周围在环境压力周围运行的过程中的湿度时，可以容忍少量泄漏，可以通过密封探针或电缆来减少。但是，当需要隔离该过程，或者当过程和外部环境之间存在较大的压力差时，必须使用具有适当安装的密封探头头。

压力leaks at the point of entry will alter the local humidity and result in false readings. In many applications it is advisable to isolate the probe from the process with a ball valve to enable the removal of the probe for maintenance without shutting down the process. See theIndigo兼容露点和温度探针DMP8with adjustable installation depth for pressurized pipelines orDew Point Temperature Transmitter DMT348也用于加压管道。

When is a sampling system needed for dew point measurement?
在可能的情况下，应将探针安装在实际过程中，以实现最准确的测量和快速响应时间。但是，直接安装并不总是可行的。在这种情况下，安装在线安装的样品单元为合适的测量探针提供了一个入口点。

请注意，外部采样系统不应用于测量相对湿度，因为温度的变化会影响测量。采样系统可以与露点探针一起使用。测量露点时，采样系统通常用于降低工艺气体的温度，以保护探针免受颗粒污染的影响，或者在不逐步降低过程的情况下易于连接和断开仪器的连接和断开。

最简单的露点采样设置由连接到采样单元的露点发射器组成。Vaisala有几种适合最常见的应用和采样需求的模型。例如，易于安装的DSC74采样单元设计用于压缩空气应用中的流量和压力条件。在苛刻的过程条件下，必须仔细设计采样系统。由于露点取决于压力，因此可能需要一个流量计，压力表，特殊的非孔管，过滤器和泵。

在加压系统中，不需要样品泵，因为工艺压力会引起足够大的抽样电池流量。当用采样系统测量露点时，应使用痕量加热，当冷却线圈或连接管周围的环境温度在露点温度的10°C内。这样可以防止将露点仪器连接到过程的管道中的冷凝。

危险环境
只有具有适当认证的产品才能在潜在的爆炸性区域中使用。例如，在欧洲，产品必须遵守自2003年以来必须强制性的ATEX指令。本质上安全的产品的设计方式即使在失败的情况下，它们也不会产生足够的能量来点燃某些类别的气体。必须通过安全性屏障隔离从本质上安全的产品进入安全区域的接线。例如，VaisalaHMT370EX一系列内在安全的湿度发射器专门设计用于危险环境。

Shock and vibration
When the probe will be subject to excessive shock or vibration, the choice of probe, mounting method, and installation location needs careful consideration.

下载智能行业的湿度指南
Measuring humidity in industrial processes and facilities usually brings you energy savings and improves end-product quality. Also indoor air quality is better when the humidity levels are optimal. Get access to Vaisala Humidity Calculator and Humidity Conversion Formulas, measurement glossary and knowledge about intrinsic safety, theoretical and practical humidity webinars and videos, a drying simulator and use cases and typical applications & instruments.Download here