The bucket tips. Light does not.
An optical rain gauge measures liquid precipitation using infrared light, without a tipping bucket, pivot or other moving mechanism. Gill’s TruMet PW100 provides a pulse output compatible with the format used by conventional tipping-bucket gauges, with one pulse per 0.1 mm of rainfall. This can simplify integration into existing monitoring systems, subject to the logger’s input and configuration requirements.
How do you measure rainfall without moving parts?
Rainfall can be measured without moving parts by detecting raindrops optically instead of collecting them in a tipping bucket. Gill TruMet PW100 detects drops across an infrared optical surface, so there is no funnel to block and no bucket or pivot to maintain. It gives the same pulse output as a tipping bucket, one pulse per 0.1 mm of rainfall.
Tipping-bucket rain gauges have been widely used in meteorological networks for decades. Rain enters a funnel and collects in a small bucket until a set volume causes it to tip. Each tip generates an output pulse representing a defined depth of rainfall.
The mechanism is familiar and widely supported, but it introduces moving parts and a funnel that can become obstructed by leaves, insects or debris. The bucket mechanism also needs to remain level and move freely. On remote installations, a blockage or mechanical fault may go unnoticed between site visits.
TruMet PW100 uses infrared optical measurement instead. Raindrops are detected across an optical measurement surface, removing the bucket and pivot mechanism. This reduces susceptibility to funnel blockage and eliminates the need to maintain a tipping mechanism, although the sensor still has application-specific operating limits.
Requirements for rainfall measurement
The choice between the two approaches depends on the existing monitoring system, the site’s exposure to debris, maintenance access and the type of precipitation that needs to be measured.
Blockage and site maintenance
Debris in a tipping-bucket funnel can prevent rainfall from being recorded. An optical gauge has no funnel or tipping mechanism, reducing these particular sources of failure. Site conditions and maintenance requirements should still be considered when selecting and installing the sensor.
Less susceptible to debris blockage
Installation and levelling
A tipping-bucket gauge must be correctly levelled so that its mechanism operates as intended. An optical gauge has no tipping pivot, removing that mechanical requirement. Correct mounting and installation remain important.
No moving parts
Logger compatibility
Many rainfall monitoring systems record pulses from a tipping-bucket gauge. TruMet PW100 provides one pulse per 0.1 mm, replicating that output format. This can support integration with an existing logger or weather station, but the receiving equipment’s electrical input, configuration and scaling should be checked before installation.
One pulse per 0.1 mm
Precipitation type and temperature
TruMet PW100 measures liquid rainfall. It does not measure snow or hail. Its stated measurement temperature range is 0 to +70°C, so the expected site conditions and precipitation type must be considered before selection.
Measurement 0 to +70°C
Comparing tipping-bucket and optical rain gauges
The two methods have different strengths. The appropriate choice depends on the measurement requirement, site conditions and the wider monitoring system.
| Consideration | Tipping-bucket rain gauge |  TruMet PW100 optical rain gauge |
|---|---|---|
| Measurement method | A bucket fills to a set volume and tips | Infrared detection of raindrops across a 66 × 20 mm optical surface |
| Moving parts | Bucket and pivot | None |
| Debris blockage | Funnel can become blocked | No funnel to obstruct |
| Output | Pulse generated by each tip | One pulse per 0.1 mm |
| Frozen precipitation | Heated versions are available from some manufacturers | Does not measure snow or hail |
| Maintenance considerations | Funnel, levelling and moving mechanism require attention | No tipping mechanism; installation and site conditions still matter |
| Typical application | Established networks and sites with regular maintenance access | Remote or long-term sites where reducing mechanical maintenance and blockage risk is important |
Neither measurement method is automatically more accurate in every application. Existing network requirements, measurement conditions and the relevant standard may favour a particular method. Where maintenance access is difficult, the absence of a funnel and moving mechanism can make optical measurement an attractive alternative.
Technical limits and selection considerations
Liquid precipitation only
TruMet PW100 measures liquid rainfall, not snow or hail. Its stated measurement temperature range is 0 to +70°C. Applications involving frozen precipitation or temperatures outside this range require a different measurement solution.
Rainfall intensity and accuracy
TruMet PW100 has a stated measurement range of 0 to 200 mm/h, with 5% accuracy. Applications involving very intense short-duration rainfall should be assessed against this range and the measurement requirements of the project.
Rain gauge or complete weather station
TruMet PW100 measures rainfall. Other parameters, such as wind speed, wind direction, temperature, humidity and pressure, require separate sensors or an integrated weather station.
Compatibility with weather stations
MaxiMet GMX550 and GMX551 are the MaxiMet models that accept the TruMet pulse input. MaxiMet GMX603 incorporates optical rainfall measurement within the weather station itself. MetConnect variants also accept TruMet through a contact-closure rain input. Confirm the exact model and interface before specifying a system.
Gill rainfall measurement products
Gill offers standalone optical rainfall measurement and weather-station options with rainfall measurement integrated or connected through a rain input.
TruMet PW100
Standalone optical rain gauge
TruMet PW100 uses infrared optical measurement to detect liquid rainfall. Its pulse output replicates the format used by conventional tipping-bucket gauges, helping it integrate with compatible monitoring systems.
MaxiMet GMX603
Compact weather station with integrated optical rainfall measurement
MaxiMet GMX603 combines optical rainfall measurement with wind, temperature, humidity and pressure measurements in a single unit. It is an option where several environmental parameters are required from a compact station without connecting a separate rain gauge.
MetConnect
Weather station with a separate rain input
TruMet PW100 connects to the contact-closure rain input on both MetConnect variants. This configuration allows rainfall measurement to be combined with the station’s other environmental measurements.
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Pulse output and system integration
Many established rainfall monitoring networks use a pulse to represent a fixed depth of rainfall. The logger counts those pulses and converts the count into a rainfall measurement.
TruMet PW100 produces one pulse per 0.1 mm, replicating the output format of a conventional tipping-bucket gauge. This can simplify replacement because the existing data system may be able to accept the same type of signal.
However, matching the pulse format does not guarantee a direct, configuration-free replacement in every installation. The receiving equipment must support the electrical input and pulse characteristics, and its scaling and recording configuration must be appropriate.
For a replacement project, check the logger model, input specification, pulse scaling and mounting arrangement before installation. These checks help establish whether the change can be made without wider system modifications.
The full explanation is in Optical rain gauge vs tipping bucket rain gauge
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Speak to our team
Tell us what you need to measure, where and under what conditions. We’ll help you work out the appropriate approach.
Frequently asked questions: rainfall measurement
A tipping-bucket rain gauge collects rain in a funnel and directs it into a small bucket. When the bucket reaches a set volume, it tips and generates an output pulse representing a defined depth of rainfall. The mechanism is widely used, but the funnel can become blocked and the moving parts need to remain level and free to operate correctly.
An optical rain gauge uses light to detect raindrops passing through or across an optical measurement area. TruMet PW100 uses infrared optical measurement and has no tipping bucket or pivot mechanism. Its output is one pulse per 0.1 mm of rainfall, providing a tipping-bucket-compatible signal for suitable monitoring systems.
Yes. An optical rain gauge such as Gill TruMet PW100 is an alternative where liquid rainfall needs to be measured without a tipping mechanism. It removes the funnel and moving parts associated with a conventional tipping-bucket gauge and provides a pulse output of one pulse per 0.1 mm. Suitability depends on precipitation type, operating conditions and system compatibility.
No. TruMet PW100 measures liquid rainfall and is not specified for measuring snow or hail. Its stated measurement temperature range is 0 to +70°C. Applications involving frozen precipitation or temperatures outside this range need a different measurement solution.
TruMet PW100 has a rainfall intensity range of 0 to 200 mm/h and an accuracy of 5%. MaxiMet GMX603 is specified at 5% accuracy or better for its integrated optical rainfall measurement. Confirm the current datasheet and applicable measurement conditions when assessing suitability for a particular project.
MaxiMet GMX550 and GMX551 are compatible models, and both MetConnect variants accept TruMet through a contact-closure rain input. MaxiMet GMX603 has optical rainfall measurement built in, so it does not require a separate TruMet rain gauge for that function. Confirm the exact model, interface and configuration before installation.
Potentially, provided the existing logger supports the required pulse input and electrical characteristics. TruMet PW100 outputs one pulse per 0.1 mm, matching the stated tipping-bucket output format. However, pulse scaling, input compatibility, configuration and mounting should be checked before treating it as a direct replacement.
Not necessarily. Accuracy depends on the instrument, rainfall intensity, installation, operating conditions and measurement requirements. Optical measurement removes the tipping mechanism and reduces susceptibility to funnel blockage, but that does not establish that it is more accurate in every application. Compare the specifications and suitability of both methods against the requirements of the monitoring network.