Current Instrumentation Solutions for a Modernized his

CURRENT INSTRUMENTATION SOLUTIONS FOR A MODERNIZED HIS

Module 2:

Mark HeggliInnovative Hydrology, Inc.

Consultant To The World BankExpert Real-Time Hydrology Information Systems

Examples that refer to products are intended for illustrative purposes only, and do not imply an endorsement or

recommendation of any particular product

Instrumentation• Surface Water Level• Discharge• Ground Water• Rainfall• Data Logger

Water Level:• Two categories of water level sensors

• Contact and Non-Contact Solution• What is a Contact and Non-Contact Solution?

• Contact• Sensor has components that are in contact with the water being measured• Susceptible to debris, water pollution damage• Includes:

• Shaft Encoder/ Stilling Well• Bubbler• Submersible Pressure Transducer

• Non- Contact• Sensor components are not in contact with the water being measured• What flows in the water and any water pollution will not interfere or otherwise

foul the sensor• Includes:

• Ultrasonic Sensor• Radar

Water Level - Contact:

Stilling Well/Shaft Encoder• Concept

• Water comes into the stilling well through inlet pipes from the water source• As water level increases and decreases, a float moves up and down with the water level• A tape attached to the float turns a wheel which is connected to the shaft on the encoder.

As the wheel turns so does the shaft.• The shaft encoder will convert the shaft rotations to an electronic signal, which will be

measured by a data logger

• The components of this type of gauge include:• A stilling well• Inlet pipes from the water • Float and weight• Tape • Wheel• Shaft encoder Water Inlet

Float


Stilling Well/Shaft Encoder Continued• Installation

• The civil works for this type of station is among the most expensive, while the sensor and associated equipment is among the least expensive sensor solutions • Construction cost of the stilling well

• Ideal Location• Stable river beds where the channel does

not change• Not a lot of sedimentation


Stilling Well/Shaft Encoder Continued• Advantages

• Low cost of equipment• Never needs to be calibrated, but only checked and reset to an outside staff gauge

• Disadvantages• Expensive civil works• The stilling well requires occasional flushing to remove sediments that may have collected

at the bottom of the stilling well. If left unchecked, the sediments could eventually block the inlet/outlet pipes


Bubbler

• Concept• The bubbler is a stage

measurement device that has a non-submersible sensor.

• The bubbler, also known as a gas-purge system allows a small quantity of air or inert gas (e.g. nitrogen) to bleed through a pipe or tubing to an orifice in the stream.

• The pressure of the gas that displaces the liquid in the orifice is then measured by a pressure transducer.

Non- Submersible Pressure Transducer


Bubbler Continued• Components

• Compressor• Orifice Line• Pressure Transducer• Tank• Desiccant


Bubbler Continued• Two Types

• Non- continuous• Only turns on at a set time

• This allows water to feed back up orifice line so the line needs to be purged and stabilized• Continuous

• Keeps the orifice line under pressure by producing approximately 1 bubble per second

• Ideal Location• Open Channels and Reservoirs• Stable river bed where channel does

not change• Not a lot of debris or sedimentation

that can cover the orifice inlet• Great option if there is not a bridge or

platform near by to put a radar or ultrasonic sensor


Bubbler Continued• Advantages

• It’s a Non-Submersible Pressure Transducer• Elimination of risk or damage of the most expensive part (pressure transducer and

compressor)• Orifice line (least expensive component) only part in the water

• Install is relatively inexpensive compared to the stilling well for the shaft encoder

• Disadvantages• Expensive compared to shaft encoder, ultrasonic sensor and submersible

pressure transducer• Desiccant replacement• Not suitable for changing channel and debris


Submersible Pressure Transducer• Concept

• The pressure exerted on the sensor by the head of water above the sensor is converted to depth.

• Components• Submersible Pressure Transducer• Pipe


Submersible Pressure Transducer Continued• Installation

• The transducer is installed in a pipe below the minimum water line.• Ideal Setup

• A submersible transducer should be avoided in open channels• It is more appropriately used in wells to measure ground water, or in lakes where the occurrence of

damaging debris or toxic water is not an issue.


Submersible Pressure Transducer Continued• Advantages

• The main advantages of a submersible pressure transducer is that the sensor requires the simplest installation • As the sensor only needs to be run down a pipe to some level that is lower than the

expected minimum water level. • The submersible pressure transducer is also one of the lowest cost sensors

(ranging $1,000- $1500)• Disadvantages

• The main disadvantage is the sensor is a contact solution and in contact with the water and all debris in the water

• In the event of a flood, the debris in the river can sweep the sensor away • These sensors are also more susceptible to damage caused by lightning striking

the water • Require calibration that usually requires the sensor to be sent back to the factory

Water Level:

• Non- Contact Sensors• Ultrasonic Sensor• Radar

Water Level - Non-Contact:

Ultrasonic Sensor• Concept

• The ultrasonic sensor measures the distance of target objects (water surface) by sending pulsed ultrasound waves at the object and then measuring the time for the sound echo to return. Knowing the speed of sound, the sensor can determine the distance to the object.

• Components• Sensor• Mounting Platform• Pipe


Ultrasonic Sensor Continued• Installation

• Requires some sort of bridge or platform to mount the sensor• Sensor must not have any object within the area of signal projection• Should be mounted where it can easily be accessed to repair if necessary

• Ideal Location• Need a Bridge or Platform directly

over water• Not practical in reservoirs or rivers

with shallow slopes• More ideally suited for canals• Measurement distance up to 10m


Ultrasonic Sensor Continued

• Disadvantages• Disadvantages are that you

need some structure to mount the sensor (bridge railing or boom)

• Measurement is not as accurate or precise as other measurement techniques, usually being within .1 % of full scale. This accuracy is generally sufficient on small bodies of water such as creeks and small canals

• Advantages• The advantage to the ultrasonic sensor is the price (around $1000 USD)• Non-contact method of measurement. The measurement is generally

unaffected by the transparency, reflectivity, opacity or color of the target


Radar• Concept

• The radar works by releasing electromagnetic energy, which is reflected by objects with high dielectric properties (ex: metal and water).

• The distance reflected by the microwave energy is determined by the measurement of the time of flight divided by the speed of light, known as Time-Domain Reflectometry (TDR)

• Various frequencies from 1 Ghz to 30 Ghz are typically used, with the higher the frequency, the more accurate and more costly the device

• Components• Radar• Mounting Platform• Pipe


Radar Continued• Installation

• Requires some sort of bridge or platform to mount the sensor• Sensor must not have any object within the area of signal projection• Should be mounted where it can easily be accessed to repair if necessary

• Ideal Location• Radars are ideal for use in moist, vaporous, and dusty environments as

well as in applications in which temperatures vary• Radar requires some structure (bridge railing or boom) to be mounted on • The water channel would need to be constant beneath the radar or a

moveable device would need to be designed so that the radar can be placed above the channel if it moved


Radar Continued• Advantages

• Non-Contact Solution• Radar will penetrate temperature and vapour layers that may

cause problems for other techniques, such as ultrasonic • Compared to the ultrasonic, radars provide a solution with a larger

distance from the water surface and a higher accuracy. The radar sensor improves the accuracy to approximately 0.03% of full scale and can have a maximum range of 22 meters to the target

• Disadvantages• Need a bridge or platform to mount• More expensive than Ultrasonic

Discharge• Contact• Non- Contact

Discharge - Non-Contact:

Radar Discharge• Concept

• There are two sensors incorporated in the device, one sensor measures the Doppler velocities of the water at the surface of the water, and the other sensor determines the depth of water

• The Doppler radar discharge system generally measured velocity over one area and makes assumptions on the velocity profile, both horizontal and vertical aspects. A profile of the channel must be made and provided to the Doppler radar discharge sensor’s algorithm so that the discharge approximation can be calculated


Radar Discharge Continued• Installation

• Simple and Inexpensive• Mounted to existing bridge or platform

• Ideal Location• The system works optimally in well-defined

symmetric channels, such as canals. • The measurement also works best on creeks

and smaller rivers, where the area where the radar velocity measurement is made represents the flow in the channel.

• The device is challenged to provide accurate discharge measurements in a larger river where the area Doppler radar measurement does not represent the flow over the entire channel. This can happen if there are actually multiple channels within the river cross-section, or there is some other bifurcation of flow.

• Channels that are complex may require multiple Doppler radar discharge sensors.


Radar Discharge Continued• Advantages

• The Doppler radar discharge sensor is a non-contact sensor which is an enormous advantage to the Acoustic Doppler Current Profiler (ADCP)

• Disadvantages• A bridge or some other support structure is required to mount the equipment• The operator of these devices must understand the assumptions in order to

determine if the sensor will provide usable measurements• The Doppler radar discharge instrument can be expected to cost between

$10,000 and $15,000 USD

Discharge - Contact:

Acoustic Doppler Current Profiler (ADCP)• Concept

• The ADCP relies on SONAR which uses sound waves to determine the distance to targets.

• The Doppler Effect is used to resolve the speed of the targets. • The ADCP operates by determining the velocity of water across the

cross section. • Types

• Up Looking• Side Looking• Down Looking


ADCP Continued• General

• The Acoustic Doppler is optimally suited for canals, estuaries, river deltas, and river reaches that experience backwater that can be protected from debris moving in the current

• Acoustic Doppler is especially effective in tidal areas or in the ocean to measure current, where current changes even though the water level stays the same

• This is not a suitable solution for streams where debris such as logs and moving rocks can dislodge and possibly damage this expensive sensor

• An increasing number of Acoustic Doppler systems are being installed in open channels since it removes the effort associated with obtaining the stage-discharge points


ADCP Continued• Up Looking

• Upward looking ADCP is where the ADCP is placed at the bottom of the channel. The upward looking ADCP will need to be programmed with the shape of the channel in order for the discharge calculations to be accurate

• Ideal Location• This is a good application in a canal where the water is generally free from

sediment and debris


ADCP Continued• Side Looking

• The side looking ADCP is place on one of the banks of a channel and project across the channel. The shape of the channel will need to be set in the ADCP for calculations to be accurate

• Ideal Location• A side looking ADCP is typically deployed in an open channel application, which

reduces the chance for sediment covering the sensor and keeps the sensor out of the way of the quickest current which also carries debris that could eventually destroy a bottom mounted ADCP


ADCP Continued• Down Looking

• The down looking ADCP is a non-permanent ADCP. The down looking is usually attached to some small floating device that can be pulled across the stream

• Ideal Location• The Down looking ADCP is a good solution for tidal situations and large areas that

the other ADCP’s cannot accurately calculate


ADCP Continued• Advantages

• Acoustic Doppler is an approach to measuring discharge that allows for the measurement without the need of a stage-discharge curve

• Disadvantages• Though many acoustic Doppler devices are very rugged, the approach relies on the sensor

being in contact with the water

Ground Water• Concept

• Ground water is most commonly measured with a submersible pressure transducer • The submersible pressure transducer measures pressure of the head water to

calculate the water depth

• Often with ground water stations, there is not a lot of room to house an external data logger, solar panel and external battery. With space being a concern, many advances in the industry have been made to accommodate the needs of the operators

• Many ground water submersible pressure transducers come with internal batteries; internal data logger and some have options with small GSM or GPRS antennas for communication

Ground Water Continued• Installation

• The transducer is installed in a pipe below the minimum water line

Ground Water Continued• Advantages

• Internal data logger• Disadvantages

Rain Gauge• Concept

• The tipping bucket is comprised of two buckets which rotate in collecting rainfall. As one bucket is filled, it empties, and moves the other bucket in place. The tipping action of the bucket activates circuitry that produces a switch-closure which can be measured by data loggers

• Components• Siphon and non- siphon

• Non-Siphon• Siphon

Rain Gauge Continued• General

• Not all tipping bucket rain gauges are created equally. Better gauges employ highly corrosion resistant powder coated metal or stainless steel. Tipping buckets themselves may have greater resistance to movement causing irregularities during the tipping moment

• Tipping bucket rain gauges need maintenance and calibration. The funnel must be kept clear of debris, and insects need to be kept out of the gauge body. Calibration is easily performed, and should be performed on at least an annual basis. It is understandable that the calibration should be performed just prior to the rainy season

• Tipping bucket rain gages are not well suited for the measurement of mixed phase or frozen precipitation, as the gauge must be heated to convert the frozen precipitation to liquid. The heating causes loss of precipitation due to evaporation. The tipping bucket solution should be avoided if frozen precipitation is expected to occur

Rain Gauge Continued• Advantages

• Tipping bucket rain gauges are relatively inexpensive, usually being less than $1,000 USD.

• Less maintenance then the storage gauge• Disadvantages

Data Logger• Concept

• A Data logger provides a hydrometric station with the capability of making measurements from electronic sensors, storing the data, and transmitting data from a variety of radio solutions

• Data loggers can nominally trigger measurements and data collection and storage device that records any desired data that is measured by the sensors.• This includes all digital and analog hydrological and meteorological sensors • This includes battery power, charge state, and charging power, which is used primarily by

maintenance technicians• Data loggers come with an array of logging capabilities and depending upon the

frequency of recordings and memory of the logger, multiple years’ worth of data can be stored

• Data loggers can take both digital and analog inputs and should be able to record multiple sensors simultaneously

• Any frequency of recording can be established by the user depending upon the needs

Data Logger Continued• Installation• Logger Types

• Vary in price and capabilites

QUIZ

a. Shaft Encoder

b. Radar

c. Bubbler

d. Ultrasonic Sensor

e. Side Looking ADCP

Which of the following sensor types are the best suited for this location?

Quiz• Concept

The End

Questions?

Current Instrumentation Solutions for a Modernized his

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