Tipping Bucket Rain Gauge (TBRG) Operation and Calibration

Tipping Bucket Rain Gauge Tipping Bucket Rain Gauge (TBRG) Operation and (TBRG) Operation and

CalibrationCalibration

Hydrography Basics Course No. 27743

What is a TBRG?What is a TBRG?Rim Rim – of known diameter (usually 200mm or 203mm) which catches precipitation

FunnelFunnel – which channels precipitation into the measuring chamber

Bucket AssemblyBucket Assembly – each bucket tip sends voltage free switch closure by means of a reed switch

SyphonSyphon– controls flow of water into bucket assembly

Syphon V Non-syphon?Syphon V Non-syphon?

• Syphon allows a TBRG to deliver Syphon allows a TBRG to deliver consistentconsistent results during low AND high rainfall intensities. results during low AND high rainfall intensities.

• Syphon allows the TBRG to be accurately Syphon allows the TBRG to be accurately calibrated over a wide range of intensitiescalibrated over a wide range of intensities

• Non-syphoning models are calibrated Non-syphoning models are calibrated accurately at ONE rainfall intensity only (e.g. accurately at ONE rainfall intensity only (e.g. 50mm/hr)50mm/hr)

Calibration ProcedureCalibration Procedure

ForFor

Tipping Bucket Rain Tipping Bucket Rain GaugesGauges

BurettingBuretting

‘‘Buretting’ ensures:Buretting’ ensures:

1.1. Buckets tip at Buckets tip at correct ‘practical’ correct ‘practical’ readingreading

2.2. Buckets tip Buckets tip ‘evenly’‘evenly’

Bucket Capacity Bucket Capacity

• The The theoreticaltheoretical value is the volume value is the volume of water in the bucket that will cause of water in the bucket that will cause it to tipit to tip– e.g. A 200mm catch with a 0.2mm e.g. A 200mm catch with a 0.2mm

bucket will theoretically tip at 6.28mLbucket will theoretically tip at 6.28mL

0.2mm

Bucket Capacity CalculationBucket Capacity Calculation

Theoretical ValueTheoretical Value

200mm

For 200mm diam. Catchment with 0.2mm bucketFor 200mm diam. Catchment with 0.2mm bucket

Volume = Volume = ππ × × rr² ² × h× h= = ππ ×10 cm² × 0.02 ×10 cm² × 0.02

cmcm= 6.28 cm³= 6.28 cm³= 6.28 mL= 6.28 mL

Bucket capacityBucket capacity

• The The practicalpractical value is less than the value is less than the theoretical to compensate for the theoretical to compensate for the extra water that enters the bucket extra water that enters the bucket during the tipping cycleduring the tipping cycle

‘‘Practical Value’ applies to ‘Syphoning’ Rain Gauges only!!Practical Value’ applies to ‘Syphoning’ Rain Gauges only!!

Calibration Set UpCalibration Set Up

Catch Height

Syphon

Nozzle

TB3 Standard Calibration TB3 Standard Calibration Data Data (200mm diam. catchment)(200mm diam. catchment)

* Based on BOM Specification (20mm equivalent rainfall)* Based on BOM Specification (20mm equivalent rainfall)

Bucket Bucket SizeSize

TheoreticalTheoretical

ValueValuePracticalPractical

ValueValueTheoreticTheoretical No. of al No. of tips per tips per

653ml* of 653ml* of waterwater

0.2mm0.2mm 6.28ml6.28ml 5.20ml5.20ml 103.9103.9

0.5mm0.5mm 15.69ml15.69ml 14.40ml14.40ml 41.641.6

1.0mm1.0mm 31.39ml31.39ml 29.50ml29.50ml 20.820.8

Bucket Tip SequenceBucket Tip SequenceSet at ‘Theoretical Value’Set at ‘Theoretical Value’

Bucket beginsto tip @ 6.28mL

~350ms aftertip began…bucket holds6.28 + ?? mL

Bucket Tip SequenceBucket Tip SequenceSet at ‘Practical Value’Set at ‘Practical Value’

Bucket beginsto tip @ 5.2mL

~350ms aftertip began…

bucket holds6.28mL

Syphon/No Syphon Syphon/No Syphon compared at each ratecompared at each rate

25, 50, 100, 200, 300, 25, 50, 100, 200, 300, 500mm/hr500mm/hr

25mm/hr @ 2x25mm/hr @ 2x

WithSyphon

WithoutSyphon

50mm/hr50mm/hr

WithSyphon

WithoutSyphon

100mm/hr100mm/hr

WithSyphon

WithoutSyphon

200mm/hr200mm/hr

WithSyphon

WithoutSyphon

300mm/hr300mm/hr

WithSyphon

WithoutSyphon

500mm/hr500mm/hr

WithSyphon

WithoutSyphon

Without a SyphonWithout a Syphon

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Without SyphonWithout Syphon

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300mm/hr


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With a SyphonWith a Syphon

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SummarySummary

All ‘syphoning’ type gauges have a distinct All ‘syphoning’ type gauges have a distinct ‘signature’, exhibited by ‘variations’ in ‘signature’, exhibited by ‘variations’ in duration of each bucket tip cycle. Primary duration of each bucket tip cycle. Primary cause:cause:

- residual water in each bucket - residual water in each bucket priorprior to to syphon dischargesyphon discharge

- variations in the flow rate of water - variations in the flow rate of water entering the gauge catchmententering the gauge catchment

‘‘Signature’ is less noticeable with increasing Signature’ is less noticeable with increasing intensitiesintensities

HS TBRG SpecificationsHS TBRG SpecificationsFeature TB3 TB4 TB6

Catchment & Rim

200mm diameter, powder coated aluminium

Enclosure Powder coated aluminium

Bucket Type Painted brass or ABS chrome plated

Painted brass (1.0mm only) or ABS

chrome plated

ABS chrome plated

Bucket Resolution

0.2mm/0.5mm/1.0mm/0.01” 0.2mm/0.5mm/0.01”

Pivots Sapphire pivot with stainless steel shaft

Stainless steel shaft and pivot

Syphon Yes No

Catchment Filter

Yes

Range 500mm/hr 300mm/hr

Accuracy ±2% 25-300mm/hr±3% 300-500mm/hr

±2.5% 0-100mm/hr±3%

100-300mm/hr

Questions?Questions?

Tipping Bucket Rain Gauge (TBRG) Operation and Calibration

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