Basics of water level gauges
water level gauges
This provides a clear explanation on the overview, features, and advantages of water level gauges.
On this page, you can learn about the roles, mechanisms, structures, types, methods of use, and technical details of water level gauges.
What is a water level gauge?
Water level gauges are also known as "water level sensors" and are used to detect water levels (water surface height). Monitoring and observation are conducted to grasp water levels at sewage treatment plants, sewers, rivers, dams, reservoirs, and agricultural water systems to prevent floods and water damage. Water level gauges are often used at such water-related facilities and disaster prevention facilities.
The importance of water level gauges
The impacts of global warming, which include sudden downpours and large typhoons, have brought about frequent flooding and water damage, not only from small and medium-sized rivers but also from major rivers. By measuring the water levels of rivers and dams, dam water discharge can be controlled, such as by slowing the release of water once a certain water level is reached, making it possible to predict floods and water damage.
The tool required for performing such water level measurements is called a "water level gauge" and can be used to obtain real-time water level data. Water level gauges are used as detectors in water level monitoring systems.
Roles of water level gauges
Dams are used to manage water supplies and flood control (e.g., by adjusting river water levels in the event of flooding or drought). Not measuring their water levels would prevent water levels from being properly managed, as well as prevent the monitoring of dangerous water levels in rivers, which could lead to flooding.
Sewers keep towns and cities clean. Unless sewers are managed, sewage would overflow and cause towns and cities to become unsanitary, and would also flow into rivers and oceans, resulting in environmental damage.
Without monitoring water levels on slopes and detecting flooding in towns and cities, it would be impossible to evacuate residents in the event of a flood or understand the situation on the ground.
Types of water level gauges
The types of sensors used as water level gauges are broadly divided into "contact types" and "continuous types." Contact types include switch types and electrode types, while continuous types include immersion types, float types/guide rope types, bubble types, and ultrasonic types. There are various types of water level gauges with different measurement methods, and the most suitable method must be selected by considering factors such as the measurement site.
Because each method comes with its own advantages and disadvantages, we recommend selecting a water level gauge based on the application and usage environment. For example, in the case of float types, any float malfunctions may prevent proper measurement, whereas immersion types (pressure types) are not impacted by components such as a float. We recommend an immersion type(Pressure type) water level gauge. The table below details the features of each type.
| Output | Measurement method | Illustration | Advantages | Disadvantages | |
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| Water level gauge | Contact method (ON/OFF output) Outputs an ON/OFF signal when contact is made with water |
Switch (float) type Displays the water level depending on the location of the float on a liquid surface |
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| Electrode type Has no moving parts, but displays the water level by detecting electrical conduction when contact is made with water |
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| Continuous method (analog output) Uses analog signals to perform real-time monitoring of water levels |
Immersion type (pressure type) Displays the water level calculated based on water pressure |
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| Float type/Guide rope type Displays the water level based on the level of the float |
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| Bubble type Displays the water level by using an above-ground sensor to detect the pressure when air is released |
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| Ultrasonic type Detects the water level by measuring the time it takes for ultrasonic waves to bounce off the water surface and return |
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What is an immersion-type water level gauge?
Immersion-type water level gauges are placed on the bottom surface of a body of water and measure the water height (water level) based on the water pressure applied to the gauge. However, this is only possible when the pressure inside the tank is atmospheric pressure. Immersion-type water level gauges enable constant monitoring of the water level and are easy to set up even in narrow spaces.
The water level is proportional to the height of the water (i.e., the weight of the water above the gauge).
In other words, if the water depth is 1 meter, the reading from an immersion-type water level gauge will also indicate 1 meter regardless of whether it's in a narrow well or a wide pool.
Principle and components of immersion-type water level gauges
The measurement principle of the water level gauge is that it detects only water pressure when atmospheric pressure is applied to the rear surface of the sensor.
Advantages and disadvantages of immersion-type water level gauges
Advantages
- Easy to set up and integrate with equipment
Just secure the cable above ground and submerge the sensor part - Won't malfunction due to debris, deposits, etc.
Only water is measured with no detection of debris, etc.
Disadvantages
- Vulnerable to corrosive substances
The gauge must be made of the proper material as it conducts measurements by being placed in direct contact with the medium - Although corrosion-resistant titanium gauges are available, they are expensive
Gauge maintenance
- In locations where the gauge may be subjected to debris, perform maintenance in accordance with the level of debris, such as cleaning the tip portion of the water level gauge. (Some manufacturers offer types that allow the tip cap to be removed for cleaning.)
- Because water level gauges use the bottom surface as a reference point for measuring the upper surface of a liquid, check the output of the water level gauge yearly and contact your distributor if output is found to be abnormal.
Water level measurement FAQ
This refers to adjusting the measurable range of the water level gauge while keeping the output at 4 to 20 mA. There are two ways to make an adjustment: either by adjusting with the water level gauge itself, or by adjusting using peripheral equipment such as a distributor.
Typically, water level gauges are submerged at the bottom of the body of water and adjusted to 4 mA. However, when used for sewage, they are installed slightly higher to avoid being buried in sludge and other sediment. For example, if the gauge is raised 10 m above the bottom of the tank, an output of 10 m will be added (shifted). This enables measurement with the bottom of the tank set as 0 m.
The permissible level of electrical resistance between the water level gauge and its power supply is the load resistance. Because products with an output of 4 to 20 mA are typically limited to 600Ω, ensure that the total of connected equipment such as the distributor, arrester, display, and cable does not exceed 600Ω.
This is not a problem for water level gauges that output 4 to 20 mA. For water level gauges that output special signals, please check with the manufacturer.
Water level gauges measure the water level using water pressure. For this reason, they require correction due to the influence of atmospheric pressure (measuring of the differential pressure between the water pressure and atmospheric pressure). This function is performed by the cable's built-in atmospheric pressure reference pipe. Without it, there would be a difference in water level readings between typhoons and normal conditions.
[Additional information]
Water depth = water pressure (water pressure + atmospheric pressure) - atmospheric pressure
Purposes of the relay box
• To serve as a terminal block for converting the water level gauge cable (dedicated wire) to a general-purpose wire
• For displaying information in the field
• To release atmospheric pressure via the box
If no display is necessary, a general-purpose box can be used after being modified to include an atmospheric pressure release mechanism.
Although water level gauges are generally selected depending on their installation environment, in the case of publicly managed sewer systems and water treatment facilities, highly reliable immersion-type water level gauges are often used. It is also preferable to use models that are both easy to maintain and highly resistant to environmental factors such as corrosion.
In the case of the contact method, only two types of signals-ON and OFF-are output. In this regard, it is similar to a light switch. It is also not possible to set precise thresholds.
On the other hand, the continuous method type uses analog output. Analog output types primarily include current types (4 to 20 mA) and voltage types (0 to 10 V) that allow precise thresholds to be set.
Please contact your local retailer for details.
Although some water level gauges and peripheral equipment have built-in arresters, they are not included on distributors and we highly recommend installing one for added protection. If used with any peripheral equipment that has a built-in arrester, this will provide an extra layer of protection. Also, because arrestors are more inexpensive and easier to replace than peripheral equipment, we recommend their installation.
