| Relative Humidity Range | Select a range that covers the lowest and highest expected humidity with a safety margin. | Common range: 0–100% RH, non-condensing. | A sensor operating near its limits may have reduced accuracy or slower recovery. | Verify the stated operating range is wider than the process range by approximately 5–10% RH where possible. |
| Humidity Accuracy | Match accuracy to the application risk and control tolerance. | Typical specifications: ±2% RH to ±5% RH, often at 20–25°C and mid-range humidity. | Accuracy generally varies with temperature, humidity level, and sensor aging. | Check accuracy at the actual temperature and humidity points required by the application. |
| Temperature Measurement | Choose a temperature range and accuracy suitable for compensation and environmental monitoring. | Common range: −40°C to 85°C; typical accuracy: ±0.2°C to ±0.5°C. | Relative humidity is temperature-dependent, so reliable temperature data improves RH interpretation. | Confirm the sensor maintains the required accuracy across the complete installation range. |
| Condensation Protection | Use a sensor designed for the risk of condensation, splash, or temporary saturation. | Look for non-condensing operation, protective filters, and a stated recovery procedure after saturation. | Liquid water can temporarily disturb readings and may damage an unprotected sensing element. | Review the enclosure rating, filter design, and recovery time after exposure to high humidity. |
| Response Time | Select a response time based on how quickly humidity changes in the monitored space. | Many digital humidity sensors specify a response time of about 5–30 seconds under defined airflow conditions. | A slower sensor may miss short excursions or delay alarms and control actions. | Compare response-time test conditions, including airflow, temperature, and humidity step size. |
| Dew Point Calculation | Include dew point when condensation prevention or compressed-air monitoring is required. | Dew point is calculated from temperature and relative humidity; accuracy depends on both inputs. | Dew point indicates the temperature at which condensation may begin under the measured pressure. | Confirm whether the device supports pressure compensation when used in pressurized systems. |
| Ethernet Communication | Select an interface compatible with the existing network and monitoring software. | Common options include 10/100 Ethernet, TCP/IP, HTTP or HTTPS, Modbus TCP, and SNMP. | Protocol compatibility determines how easily data can be integrated into a PLC, SCADA, BMS, or cloud system. | Test data polling, register mapping, alarm transmission, and network reconnect behavior. |
| Power Supply | Choose a power method supported by the installation location and network infrastructure. | Typical requirements include 12–24 VDC or Power over Ethernet, depending on the design. | Power compatibility affects wiring, installation cost, and uptime during network or electrical interruptions. | Verify voltage tolerance, power consumption, PoE standard compatibility, and restart behavior. |
| Enclosure and Installation | Match the enclosure and mounting method to the environment and airflow pattern. | Indoor installations often use IP30–IP54 protection; dusty or wet areas may require higher protection. | Poor placement or blocked airflow can cause delayed or unrepresentative readings. | Install away from direct sunlight, heaters, vents, water spray, and stagnant air pockets. |
| Calibration and Long-Term Stability | Define a calibration interval based on required uncertainty, operating conditions, and audit rules. | A practical verification interval is often 6–12 months, but harsh environments may require more frequent checks. | Humidity sensors can drift over time, especially after exposure to contaminants or prolonged high humidity. | Require traceable calibration records, adjustment capability, and a defined sensor replacement policy. |
| Data Logging and Alarms | Choose logging capacity, sampling interval, and alarm functions based on the monitoring objective. | Common sampling intervals range from 1 second to 1 minute; alarm limits should include hysteresis and delay settings. | Historical data supports compliance, troubleshooting, trend analysis, and evidence of excursion handling. | Confirm timestamp accuracy, data export format, alarm notifications, and behavior during network outages. |