Accurately measuring rainfall has long been a challenge, owing to its pronounced regional and diurnal variability. The emergence of modern Western scientific methods spurred systematic efforts to develop automated, quantitative rain gauges. Among the early pioneers was Benjamin Franklin, whose work contributed to a growing body of research that produced a diverse range of gauge designs, varying in form and operating principle across different countries and eras.
Research has since shown that measurement accuracy depends on several key factors: the material of the gauge, the diameter of its opening, the height of the opening above the ground, and the characteristics of the surrounding environment. Today, most rain sensors are manufactured from durable, impact-resistant plastics, a practical evolution driven by the need for long-term reliability in the field.
What is a rain gauge?
A rain gauge is an instrument used to measure the amount of precipitation falling over a given area within a set period of time. (Snowfall is measured separately using a snow gauge.) Rain gauges come in many varieties, but most report measurements in millimeters, though inches and centimeters are also used in some regions.
Readings can be collected manually or through an automated weather station, and the frequency of observation is typically adjusted to meet the needs of the collecting agency. In most cases, the collected water is discarded after each reading. However, some weather stations retain samples for further analysis, such as testing for pollution levels or other environmental indicators.
How does a rain gauge work?
The rain gauge working principle is straightforward. The tipping bucket rain gauge, one of the most common designs, operates on a simple seesaw mechanism. As rainwater collects in a small bucket mounted on a pivot, it gradually accumulates until its weight tips the bucket to one side, triggering a signal to an electronic recorder. The bucket then resets, and the process repeats.
| Internal structure of tipping bucket rain gauge | |||
|---|---|---|---|
| Number | Explain | Number | Explain |
| 1 | Base | 7 | Funnel |
| 2 | Support plate | 8 | Magnetic steel |
| 3 | Leveling nut | 9 | Partition |
| 4 | Tipper bracket | 10 | Reed switch |
| 5 | Bearing screw | 11 | Outlet funnel |
| 6 | Tipping bucket | 12 | Bracket |
Each tip corresponds to a fixed amount of rainfall, typically 0.2 mm or 0.5 mm depending on the gauge. The recorder tallies the number of tips over time and transmits the data to a computer, where it is processed and displayed as statistical charts or rainfall graphs.
What is a rain gauge used for?
Rain gauges serve a fundamental role in meteorology by providing timely, accurate records of precipitation. Different types are suited to different measurement needs.
The tipping bucket rain gauge is a wired telemetry instrument designed for continuous monitoring. It records both the rate and accumulation of precipitation over time, and consists of two main components, a sensor and a recorder, connected by a cable.
The siphon rain gauge is similarly capable of continuous recording, capturing not only the total amount of precipitation but also the duration of each rainfall event. Its upper funnel shares the same dimensions as that of a standard rain gauge, ensuring consistency in data collection.
The standard rain gauge, by contrast, is designed specifically to measure accumulated precipitation over a defined period rather than record it in real time. Its cylindrical outer shell is typically made of transparent glass or plastic, allowing the water level to be read directly. Rainwater is channeled through a funnel into a narrow storage tube at the base, which concentrates the collected water to improve reading precision.
Types of rain gauges
Rain gauges are available in a wide variety of designs, each differing in appearance and underlying measurement principle. Some are built to capture instantaneous rainfall rates, while others record total accumulated precipitation. Some operate on mechanical principles, others on optical ones. Despite these differences, all rain gauges share the same core purpose: delivering accurate, reliable precipitation data for a given area.
This article focuses on four of the most widely used types:
- Standard rain gauge
- Tipping bucket rain gauge
- Optical rain gauge
- Weighing rain gauge
Standard rain gauges
The standard rain gauge is one of the most widely used and cost-effective options available. Installation is simple: the gauge only needs to be placed in an open area with unobstructed exposure to rainfall.
Its operating principle is straightforward. Rainwater falls into a funnel-shaped collector at the top, which channels the water down into a narrow measuring tube. Because the collector’s diameter is ten times that of the tube, the water level inside the tube rises at ten times the rate it would in an open container of the same width. This magnification effect allows precipitation to be measured to a precision of one-hundredth of an inch.
When rainfall exceeds the capacity of the measuring tube, the overflow is held in the outer housing of the gauge. The recorder can then empty the tube, measure the overflow separately, and combine the readings for a complete total.
Standard rain gauges reading
Recording rainfall using a standard or funnel rainfall gauge is usually done manually. It is important to be as accurate as possible when reading the meter. When taking the reading, the rain gauges must be kept level, and your line of sight must be flush with the water surface in the instrument, and read the lowest point of the sunken water surface. The reading should be accurate to one decimal place.
If the amount of precipitation is large and the amount cannot be completed at one time, it can be divided into multiple amounts. After each measurement, it shall be recorded and the total amount of precipitation shall be accumulated. In the event of solid precipitation such as ice and snow, the funnel should be replaced with a snow-bearing port, so that the solid precipitation can directly fall into the rain gauge (the water storage bottle should be covered to prevent evaporation), and it should be placed in a warm place or added Quantitative warm water (boiling water cannot be used or too much added). After the ice and snow are melted, measure with a measuring cup, and then subtract the added warm water from the measured result to get the measured solid precipitation.
Standard rain gauges installation
Place the standard rain gauges on a fixed shelf in the observation area. The mouth of the organ is kept level, 70 cm above the ground. In areas with deep snow in winter, a backup shelf that can make the height of the rain gauge reach 1.0-1.2 meters from the ground should be installed nearby. When the snow depth exceeds 30 cm, the instrument should be moved to the backup shelf for observation.
When it snows in winter, the funnel must be unscrewed from the mouth of the device (for stations with old rain gauges, the snow bearing mouth must be replaced), the water storage bottle shall be taken away, and the snow bearing mouth and water storage tank shall be used directly to hold the precipitation.
Standard rain gauges maintenance
- After the precipitation stops in the warm season, supplementary observations should be made immediately to avoid excessive evaporation and incorrect precipitation measurement.
- The measuring cylinder and water storage bottle of the rain gauge should be kept clean frequently and should be cleaned and inspected at least once a month.
- Don’t check the cylinder for leaks in winter or rainstorm season.
- Every time you check the equipment and equipment, you should pay attention to whether there is any blockage in the water holder and the water funnel, and whether there is any debris such as sharp soil, leaves, etc. in the water cylinder. If there is any debris, it should be removed immediately.
Tipping bucket rain gauges
The tipping bucket rain gauge is a weather sensor designed for greater measurement complexity and accuracy than a standard gauge. It is commonly paired with outdoor weather stations and offers a key practical advantage: fully automated readings that eliminate the possibility of human error. The tipping bucket rain gauge is widely regarded as a highly accurate rainfall measuring instrument.
How does a tipping bucket rain gauge work? It operates based on the tipping bucket principle, which detects changes in rainfall in real time. The sensor uses a mechanical bistable structure with two small buckets. When one bucket collects a certain amount of rainwater, it tips over due to gravity and empties, while the other bucket moves into position to collect water. Each tipping action generates a pulse signal. These signals are recorded and transmitted to a cloud server via wired or wireless communication.
At present, the materials of tipping bucket rain gauge commonly used in the market are professional stainless steel rain gauges and cheap ABS rain gauges.
Tipping bucket rain gauges reading
Tipping bucket rain gauges record rainfall automatically, feeding data into an intelligent rainfall monitoring system that transmits readings to a central data center via RS485, analog, GPRS, Ethernet, or other communication methods.
Users can access the data via a computer or mobile app. The platform allows them to view rainfall trends in the form of curves, including hourly, daily, monthly, and annual rainfall. Historical data can also be exported and saved as Excel files for further analysis, research, and inspection.
The system is capable of continuous monitoring and full process tracking. It integrates data collection, recording, and storage, and also supports remote diagnosis and control functions.
Tipping bucket rain gauges installation and commissioning
- The installation height of the rainfall sensor is 0.7m (the distance from the plane of the bearing aperture to the ground of the observation site) for the continuity and comparability of the observation data in this area. The height of 1.2m can also be used in the some area.
- When the rain sensor is installed, use a level to level the rain-bearing mouth.
- The installation holes of the three feet on the base of the rain sensor are fixed on the concrete base with three M8 anchor bolts and spirals (or expansion screws). The depth of the base buried in the soil should be able to ensure that the instrument is installed firmly and will not shake or tilt in a storm.
- Note: When pouring the foundation concrete, it should be ensured that the three anchor bolts are divided into 120 equal parts.
- Adjust the leveling screw to center the round bubble. After the instrument is leveled, slowly tighten the three fixing screws. If the level bubble changes, readjust it again. Hold it firmly.
- The base should have drainage pipe outlets and cable channels. If it is necessary to collect the drainage volume to test the measurement accuracy of the system, a small room (pit) for the collection container should be constructed.
- The signal output cable is a two-core shielded cable (A43VVT2*16/0.15 microphone cable).
- The cable is inserted through the rubber cable sheath of the instrument base and locked with a screw cap to increase the tensile strength and prevent the wiring from pulling off. The two-core wires of the cable are stripped 20mm in length, folded in half, twisted into strands, inserted into the two wiring holes of the commonly used signal-transmitting parts in the terminal block, and fastened with screws.
- Gently dial the parts of the tipping bucket with your hand to check whether the signal of the receiving part is normal.
- Perform manual water supply verification.
- Put the rain receiver components on the base of the instrument. At this point, the instrument is installed.
Tipping bucket rain gauges maintenance
- First, protect the physical integrity of the instrument. The gauge opening must not be deformed, and the body must remain stable and level. Annual checks with a vernier caliper and spirit level are recommended. Unattended stations should have additional protective measures in place.
- Second, keep all water channels clear. Depending on local conditions, regularly remove silt, dust, leaves, insects, and other debris from the funnel, channels, and inner surface of the rain receiver to ensure unobstructed water flow.
- Third, keep the tipping bucket clean. If mud or sand accumulates in the water chamber, clean it with water or alcohol using a soft cotton swab. Avoid touching the inner wall of the bucket with bare fingers, as skin oils can affect measurement accuracy.
- Fourth, maintain the jewel bearings carefully. If the tipping mechanism feels stiff or resistant, clean the shaft journals and bearing holes with water or alcohol. Do not apply oil to jewel bearings, as dust particles drawn in by the oil act as an abrasive and accelerate bearing wear. Because jewel bearings are hard and brittle, they must be handled and assembled with care. If a bearing is worn or broken, replace it promptly along with the bucket shaft if damaged.
- Fifth, preserve calibration. Do not arbitrarily adjust the fine-tuning screws that govern the tipping bucket’s inclination and water volume settings. Ensure the bubble level remains centered. These two conditions are the foundation of measurement accuracy.
- Sixth, protect the gauge when not in use. When the instrument is stored indoors or left unattended in dry weather, cover the opening with the tube cover to prevent dust from settling into the rain receiver.
Like the tipping bucket rain gauges, the optical rain gauge is also an automatic rain gauge, relying on built-in sensors and other accessories to automatically count rainfall, and upload the data to the cloud platform through wired or wireless means for customers to view.
Its working principle is based on optical sensing. When raindrops pass through the sampling area, they block the laser beam, causing changes in the electrical signal (such as voltage or current) received by the sensor. Once the raindrops leave the sampling area, the signal returns to its original state. By continuously scanning the size and number of raindrops in real time, the system calculates the rainfall amount and outputs the result.
Optical rain gauges installation
The rain sensor needs to be installed in an open place, and there should be no obstructions around and above it. Install the device on the bracket in the accessories first, and fix the device and the bracket with 4 M4*35 304 stainless steel screws and nuts. Then install the bracket to the position to be installed (the position to be installed needs to be opened with a φ5 round hole), the bracket should be installed horizontally, and finally the tray and the equipment are fixed by three M4*10 304 stainless steel screws and nuts.
Optical rain gauges maintenance
The rain gauge needs to be outdoors for a long time, and the use environment is very harsh. Therefore, the surface of the instrument should be kept clean and often wiped with a soft cloth. The instrument should be cleaned once a month for long-term operation and once every three months.
The rain gauges mentioned above are generally limited to measuring liquid precipitation. In contrast, a weighing rain gauge is based on the weighing principle and uses a high precision sensor to measure all types of precipitation, including solid, liquid, and mixed forms.
It continuously records the weight of collected precipitation in a storage container through a spring mechanism or a weight balancing system, and then converts the measured weight into rainfall using an electronic scale.
Weighing rain gauge installation
The first consideration is the selection of the installation location. The device should be installed in an open and unobstructed area, away from buildings, trees, and tall structures to avoid wind field interference or precipitation shielding. In general, the distance between surrounding obstacles and the instrument should be at least 2 to 4 times the height of the obstacles to ensure representative precipitation collection.
Secondly, the instrument should be installed on a stable and level foundation, such as a concrete base or a dedicated mounting bracket. This ensures that the weighing system remains level over the long term, as any tilt will directly affect measurement accuracy. During installation, a level should be used for calibration, and the device must be securely fixed to prevent displacement caused by wind or vibration.
The third aspect is the installation of the inlet and collection container. The rain gauge inlet must remain level, and the rim height should comply with relevant standards, typically around 70 cm above the ground, depending on specific requirements. It is also important to ensure that the inlet is not tilted or deformed to avoid systematic measurement errors.
The fourth consideration is drainage and protection design. Weighing rain gauges are usually equipped with drainage or overflow structures. During installation, proper drainage must be ensured to prevent water accumulation from affecting the weighing measurement. It is also recommended to install accessories such as wind shields and bird deterrent devices to reduce environmental interference.
Finally, electrical and communication connections should be completed according to the device type, such as RS485, GPRS, or Ethernet. Power supply and signal wiring must follow proper standards, with appropriate waterproofing, lightning protection, and grounding measures in place.
Weighing rain gauge maintenance
- When the instrument is used outdoors for long periods or in harsh environments, the inner wall of the rain inlet should be cleaned regularly with a soft cloth to keep it free of debris. If leaves or other foreign objects are found inside the inlet, they should be removed promptly to ensure unobstructed water flow.
- If the instrument is not used for an extended period, a cover should be placed over the inlet to protect it.
- Under normal operating conditions, the instrument should be cleaned once a month, and it must be cleaned at least once every three months.
- When the antifreeze liquid and evaporation suppression oil in the inner container are insufficient, they should be replenished as needed.
- A lightning protection safety inspection of the weighing precipitation sensor should be carried out every spring.
Conclusion
Before the Internet of Things technology was popularized, the monitoring and management of regional rainfall was relatively simple, basically relying on manual reading of data. During periods of heavy rainfall, it is difficult to obtain the latest real-time water level information.
Therefore, it is very important to choose the right measuring tools and measuring methods. Standard rain gauges are loved by meteorological enthusiasts and rainfall researchers. Tipping bucket rain gauges are often used with weather stations. The best place for the automatic rain gauge is outdoor. Optical rain gauges are of great significance to aviation and navigation. Weighing rain gauges are commonly used in scientific research observation stations and high-precision meteorological monitoring scenarios.
This article is written by the Renke Technical Team, which has extensive experience in rainfall measurement and meteorological instrumentation. The team has been involved in the design, calibration, and field deployment of multiple types of rain gauges, including tipping bucket, weighing, and optical systems, with a strong focus on measurement accuracy and long-term data reliability. Through continuous participation in real-world monitoring projects and system integration, Renke’s engineers have developed a deep understanding of precipitation measurement principles, environmental influences, and instrumentation standards that supports the accuracy and authority of the information presented in this article.
