The chemical purge option suits installation locations that are exposed to chemical pollution, such as chemical plants and roads.
In some applications the sensor gain may decrease gradually due to an interference caused, for example, by a chemical present in the measured gas. The following figure illustrates the decrease of sensor gain due to an interfering chemical and the effect of the chemical purge process.
The sensor polymer absorbs the interfering chemical which reduces the ability of the polymer to absorb water molecules and consequently the sensor gain decreases. In chemical purge, heating the humidity sensor to approximately +180 °C (356 °F) for several minutes evaporates the interfering chemical.
You can set chemical purge (startup purge) to start within 10 seconds from HMP155 startup. The purge has a heating phase and a cooling phase. After the purge cycle of 8 minutes the sensor returns to normal mode.
| Chemical purge function locks the output values for about 8 minutes. |
| CAUTION Avoid using the purge function in below freezing temperatures. Low temperatures decrease the effect of purge. It also takes the sensor longer to return to normal function. |