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Water Level loggers Vented vs Absolute
12

Water Level loggers Vented vs Absolute. Definitions Absolute: Measures total pressure (weight) above the sensor. Atmospheric pressure must be removed.

Dec 26, 2015

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Ralf Potter
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Page 1: Water Level loggers Vented vs Absolute. Definitions Absolute: Measures total pressure (weight) above the sensor. Atmospheric pressure must be removed.

Water Level loggersVented vs Absolute

Page 2: Water Level loggers Vented vs Absolute. Definitions Absolute: Measures total pressure (weight) above the sensor. Atmospheric pressure must be removed.

Definitions

Absolute: Measures total pressure (weight) above the sensor. Atmospheric pressure must be removed from this value to reveal actual water pressure (water column).

Vented: Measures only water pressure above sensor. Atmospheric vent accounts for atmospheric pressure.

Page 3: Water Level loggers Vented vs Absolute. Definitions Absolute: Measures total pressure (weight) above the sensor. Atmospheric pressure must be removed.

The mystery of barometric compensation

Pressure in cmH₂OLevel logger: 1500cmH₂O – Baro: 1000cmH₂O = 500cmH₂O

= 0.5m above the pressure sensor

ALWAYS take a manual dip measurement!

Page 4: Water Level loggers Vented vs Absolute. Definitions Absolute: Measures total pressure (weight) above the sensor. Atmospheric pressure must be removed.

How do they work?5cm

0

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Page 5: Water Level loggers Vented vs Absolute. Definitions Absolute: Measures total pressure (weight) above the sensor. Atmospheric pressure must be removed.

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Baro

Absolute

2 x Errors

Page 6: Water Level loggers Vented vs Absolute. Definitions Absolute: Measures total pressure (weight) above the sensor. Atmospheric pressure must be removed.

Pressure ranges

1m --------------------------------------------------------------------------------------

10m --------------------------------------------------------------------------------------

30m --------------------------------------------------------------------------------------

Sensitivity varies with manufacturer. Accuracy based on full scale.

Page 7: Water Level loggers Vented vs Absolute. Definitions Absolute: Measures total pressure (weight) above the sensor. Atmospheric pressure must be removed.

One size does not fit all…..High Accuracy?

100m range?

Low maintenance?

Easy to deploy?

Multiple interface options?

Long battery life?

Low cost?

120

UbUnobtanium

Page 8: Water Level loggers Vented vs Absolute. Definitions Absolute: Measures total pressure (weight) above the sensor. Atmospheric pressure must be removed.

If vented loggers are so good, why would I choose not to use them?

Vented cable: installation, vandalism, weather protection, tailor length cables/re-deployment

Cost

User interface

Maintenance

Page 9: Water Level loggers Vented vs Absolute. Definitions Absolute: Measures total pressure (weight) above the sensor. Atmospheric pressure must be removed.

When should I use a vented logger?

Critical data

External logger or telemetry?

Single installation?

Page 10: Water Level loggers Vented vs Absolute. Definitions Absolute: Measures total pressure (weight) above the sensor. Atmospheric pressure must be removed.

Why would I choose to use an absolute logger?

Maintenance free

Easy deployment

Low cost, particularly for multiple installations

Purpose made intuitive interfaces

Easy re-deployment/Versatility

Discrete

Page 11: Water Level loggers Vented vs Absolute. Definitions Absolute: Measures total pressure (weight) above the sensor. Atmospheric pressure must be removed.

What else to consider?Site access?

Equipment placement (above and below water)

Environmental/human risk?

Return visiting?

GPRS signal? (NOT THE SAME AS CALL SIGNAL)

Critical data?

Expected fluctuation?

Other parameters?

Budget?

Page 12: Water Level loggers Vented vs Absolute. Definitions Absolute: Measures total pressure (weight) above the sensor. Atmospheric pressure must be removed.

Conclusion

Is vented better than absolute? … Not necessarily

Consider your application carefully