HMP7 probe - HMP1 - HMP3 - HMP4 - HMP5 - HMP7 - HMP8 - HMP9 - HMPX - MMP8 - MMPX - TMP1 - TMPX

HMP Series with MMP8 and TMP1 User Guide

Document code
Document type
User guide
Figure 1. HMP7 probe dimensions

Vaisala HUMICAP® Humidity and Temperature Probe HMP7 is designed for applications that involve constant high humidity or rapid changes in humidity, such as drying and test chambers, combustion air, and other humidifiers and meteorological measurements, where measurement performance and chemical tolerance are essential.

  • Temperature measurement range −70 … +180 °C (−94 … +356 °F)
  • Operating temperature of probe body −40 … +80 °C (−40 … +176 °F)
  • Condensation prevention with probe heating
  • Vapor and pressure proof construction

Condensation prevention with probe heating

Condensation prevention on HMP7 uses a combination of probe heating and sensor warming. Probe heating keeps the entire probe head above the current dew point temperature, which prevents condensation from forming on the probe.

The values of output parameters that are dependent on temperature measurement (such as relative humidity) are unavailable when the probe is warming itself, unless the true temperature of the measured environment is updated to the temperature compensation register of the probe from another measurement instrument (for example, TMP1 model probe). Output parameters that can be measured or calculated without this external temperature information, such as dew point temperature, are available even without the temperature input.

The Indigo80 handheld indicator and Indigo500 transmitters support HMP7 temperature compensation from TMP1. For more information, see:

HMP7 in fuel cell applications

Probe heating makes HMP7 ideal for use in fuel cell applications, specifically proton-exchange membrane fuel cells (PEMFC). Humidity measurements in fuel cell applications are performed in a high-humidity environment, typically over 80% relative humidity. Performing humidity measurements in hot, near-condensing environments is a challenging task, and the humidity sensor must be adequately protected against saturation to allow continuous measurement. Probe heating accomplishes just that.

HMP7 can be ordered from Vaisala with special settings that have been optimized for the fuel cell application. These settings include a faster probe heating control that allows the probe to quickly heat the probe to stay ahead of the rising dew point temperature.

WARNING HMP7 is not designed for use in hazardous environments with potentially explosive atmospheres. Make sure no part of the probe is placed in a potentially explosive gas mixture.

For more information on HMP7 in fuel cell applications, see HMP7 and HMT317/337 for Fuel Cell Applications Technical Note (M212840EN).