# Sensor Lifecycle Planning

Long-term environmental monitoring requires planning for **sensor aging, mechanical wear, and environmental exposure**. This page provides guidance on recommended replacement intervals and lifecycle planning for sensors used in 3D-PAWS stations.

Sensor lifecycle planning helps maintain **data quality, system reliability, and operational continuity** by defining expected service lifetimes and replacement schedules.

Sensors may be replaced on a planned schedule or earlier if verification indicates abnormal behavior.

Planned sensor rotation also helps reduce unexpected failures and minimize long-term measurement bias.

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## Why Sensor Lifecycle Planning Is Important

Environmental sensors gradually change performance over time due to exposure to environmental conditions such as:

* humidity and condensation
* temperature cycling
* dust, salt, and pollution
* mechanical wear in moving components

Routine cleaning and inspection help maintain sensor performance, but they do not prevent long-term aging or drift.

Planned replacement allows removed sensors to be inspected, cleaned, and verified while reducing the risk of undetected sensor bias or sudden failure.

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## Environmental Exposure Categories

Replacement intervals depend strongly on environmental exposure. For planning purposes, deployments can be classified as **benign** or **harsh** environments.

#### Benign Environments

Typical characteristics include:

* dry or semi-arid climates
* inland locations away from salt spray
* low dust or pollution
* limited fog, dew, or condensation

#### Harsh Environments

Typical characteristics include:

* coastal or marine environments
* tropical or persistently humid climates
* frequent fog, dew, or condensation
* dusty agricultural or polluted environments

Stations in harsh environments typically require **shorter replacement intervals**.

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## Radiation Shield Sensor Set

The radiation shield typically contains the **air temperature, relative humidity, and pressure sensors**. These sensors are commonly replaced together to simplify maintenance and verification.

| Sensor                          | Typical Replacement Interval | Notes                                              |
| ------------------------------- | ---------------------------- | -------------------------------------------------- |
| SHT31D (humidity / temperature) | 1–2 years                    | Interval driven primarily by humidity sensor aging |
| MCP9808 (temperature)           | 1–2 years                    | Rotated with the shield sensor set                 |
| BMP390 (pressure)               | 1–2 years                    | Rotated with the shield sensor set                 |

Recommended guidance:

* **Benign environments:** replace every \~2 years
* **Harsh environments:** replace every \~1–1.5 years

Replacing the sensor set together simplifies field operations and ensures consistent verification of air temperature, humidity, and pressure measurements.

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## Wind and Precipitation Sensors

Wind and precipitation instruments are typically rotated as **complete mechanical assemblies**, since wear is usually driven by moving components rather than electronics.

| Sensor     | Typical Replacement Interval | Notes                                  |
| ---------- | ---------------------------- | -------------------------------------- |
| Wind vane  | 2–3 years                    | Mechanical bearing wear                |
| Anemometer | 2–3 years                    | Mechanical wear in rotating components |
| Rain gauge | 1–2 years                    | Remove and verify calibration          |

Guidance:

* **Benign environments:** replace every \~3 years
* **Harsh environments:** replace every \~1.5–2 years

Rain gauges should be **verified or recalibrated periodically** to ensure accurate precipitation measurements.

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## Additional Sensors

Optional environmental sensors may have different expected lifetimes depending on their sensing technology.

| Sensor                                        | Typical Replacement Interval | Notes                                  |
| --------------------------------------------- | ---------------------------- | -------------------------------------- |
| Particulate matter sensor (PMSA003I)          | 2–3 years                    | Optical sensor aging and contamination |
| Ultrasonic distance sensors (MB7363 / MB7364) | 3–5 years                    | Verify against known distance          |
| Soil moisture sensor (Tinovi PM-WCS-3-I2C)    | 3–5 years                    | Verify wet/dry response periodically   |

Note: soil sensors often require several months after installation for the surrounding soil to settle before readings stabilize.

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## Sensor Rotation and Verification

When sensors are replaced as part of planned rotation:

1. A **verified replacement sensor** is installed in the field.
2. The removed sensor is returned for **inspection and testing**.
3. Verified sensors may be reused in future deployments.

Verification may include:

* visual inspection
* functional testing
* comparison with a nearby reference station
* short-term comparison against known environmental conditions

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## Power System Components

Power system components also degrade over time due to temperature, charge cycles, and environmental exposure.

| Component                            | Typical Replacement Interval    | Notes                                    |
| ------------------------------------ | ------------------------------- | ---------------------------------------- |
| Rechargeable battery (Li-ion / LiPo) | 2–4 years                       | Depends on charge cycles and temperature |
| Solar panel                          | Replace as performance degrades | Inspect for damage or reduced output     |

Power system failures are one of the **most common causes of station outages**, so batteries and power components should be inspected regularly.

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## Data Logger and Core Electronics

Data loggers typically do not degrade gradually but may fail due to environmental exposure or power events.

| Component                                  | Typical Replacement Interval | Notes                                    |
| ------------------------------------------ | ---------------------------- | ---------------------------------------- |
| Data logger (Particle Boron or equivalent) | 5–7 years                    | Replace earlier if repeated faults occur |
| SD card / removable storage                | 3–5 years                    | Replace if read/write errors occur       |

Data loggers are usually replaced **on failure or during major station refurbishment**, rather than during routine maintenance cycles.

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## Early Replacement and Exceptions

Recommended replacement intervals represent a **maximum planned service life**, not a guarantee.

Sensors should be replaced earlier if:

* verification checks indicate drift or bias
* measurements become intermittent or erratic
* mechanical wear or contamination is observed
* environmental exposure exceeds expected conditions

Routine maintenance and verification remain essential regardless of sensor age.