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Tipping Bucket Rain Gauge (TBRG) Operation and Calibration. Hydrography Basics Course No. 27743. What is a TBRG?. Rim – of known diameter (usually 200mm or 203mm) which catches precipitation. Funnel – which channels precipitation into the measuring chamber.

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what is a tbrg
What is a TBRG?

Rim – of known diameter (usually 200mm or 203mm) which catches precipitation

Funnel– which channels precipitation into the measuring chamber

Syphon– controls flow of water into bucket assembly

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

syphon v non syphon
Syphon V Non-syphon?
  • Syphon allows a TBRG to deliver consistent results during low AND high rainfall intensities.
  • Syphon allows the TBRG to be accurately calibrated over a wide range of intensities
  • Non-syphoning models are calibrated accurately at ONE rainfall intensity only (e.g. 50mm/hr)
calibration procedure for tipping bucket rain gauges
Calibration Procedure

For

Tipping Bucket Rain Gauges

buretting
Buretting

‘Buretting’ ensures:

  • Buckets tip at correct ‘practical’ reading
  • Buckets tip ‘evenly’
bucket capacity
Bucket Capacity
  • The theoretical value is the volume of water in the bucket that will cause it to tip
    • e.g. A 200mm catch with a 0.2mm bucket will theoretically tip at 6.28mL
bucket capacity calculation

200mm

0.2mm

Bucket Capacity Calculation

For 200mm diam. Catchment with 0.2mm bucket

Theoretical Value

Volume = π × r² × h

= π ×10 cm² × 0.02 cm

= 6.28 cm³

= 6.28 mL

bucket capacity1
Bucket capacity
  • The practical value is less than the theoretical to compensate for the extra water that enters the bucket during the tipping cycle

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

calibration set up
Calibration Set Up

Nozzle

Catch Height

Syphon

tb3 standard calibration data 200mm diam catchment
TB3 Standard Calibration Data (200mm diam. catchment)

* Based on BOM Specification (20mm equivalent rainfall)

bucket tip sequence set at theoretical value

Bucket begins

to tip @

6.28mL

bucket holds

6.28 + ?? mL

Bucket Tip SequenceSet at ‘Theoretical Value’

~350ms after

tip began…

bucket tip sequence set at practical value

Bucket begins

to tip @

5.2mL

bucket holds

6.28mL

Bucket Tip SequenceSet at ‘Practical Value’

~350ms after

tip began…

syphon no syphon compared at each rate

Syphon/No Syphon compared at each rate

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

25mm hr @ 2x

With

Syphon

Without

Syphon

25mm/hr @ 2x
50mm hr

With

Syphon

Without

Syphon

50mm/hr
100mm hr

With

Syphon

Without

Syphon

100mm/hr
200mm hr

With

Syphon

Without

Syphon

200mm/hr
300mm hr

With

Syphon

Without

Syphon

300mm/hr
500mm hr

With

Syphon

Without

Syphon

500mm/hr
without a syphon

Without a Syphon

Video will play 3 times

then images enhanced

with a syphon

With a Syphon

Video will play 3 times

then images enhanced

with syphon1

100mm/hr

300mm/hr

With Syphon

01/12

with syphon2

100mm/hr

300mm/hr

With Syphon

02/12

with syphon3

100mm/hr

300mm/hr

With Syphon

03/12

with syphon4

100mm/hr

300mm/hr

With Syphon

04/12

with syphon5

100mm/hr

300mm/hr

With Syphon

05/12

with syphon6

100mm/hr

300mm/hr

With Syphon

06/12

with syphon7

100mm/hr

300mm/hr

With Syphon

07/12

with syphon8

100mm/hr

300mm/hr

With Syphon

08/12

with syphon9

100mm/hr

300mm/hr

With Syphon

09/12

with syphon10

100mm/hr

300mm/hr

With Syphon

10/12

with syphon11

100mm/hr

300mm/hr

With Syphon

11/12

with syphon12

100mm/hr

300mm/hr

With Syphon

12/12

summary
Summary

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

- residual water in each bucket prior to syphon discharge

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

‘Signature’ is less noticeable with increasing intensities