Hydrology Sensors

Stevens is the original water level measurement instrumentation company with the introduction of the widely known chart recorders introduced in 1911. Today, Stevens offers a wide selection of water level measurement sensors including robust ceramic pressure sensors, shaft encoders, acoustical sensors, and visual reference staff gages. Stevens still offers the low-powered, mechanical chart recorders for long-term uninterrupted, real-time chart of water level.

Pressure sensors

Pressure sensors like the SDX perform liquid level measurement by having the sensor submerged at a fixed level under the water surface. The pressure sensor measures the equivalent hydrostatic pressure of the water above the sensor diaphragm, using this to calculate the total liquid depth. This function of a pressure sensor can be compared to “weighing the water”. Pressure sensors are ideal for ground and surface water level applications.

Applications

  • Ground water level monitoring
  • Ground water slug testing

Advantages

  • Output can be analog or digital depending on model
  • Smaller diameter stilling well or pipe can be used for installation.
  • A low profile installation site can be achieved using pressure sensors with internal data logging.
  • Easy to install, maintain and calibrate.

Limitations

  • Typically subject to long-term drift and variations with temperatures. However, they are in the water where the temperature is usually fairly stable. It's a good idea to check calibration every 6 months.
  • Fouling or corrosion with direct exposure to the water can affect the readings.
  • Models are available in a broad pressure range that needs to be known at time of purchases.
  • Some models require breather tube in the cable to reference to atmospheric pressure for best accuracy.
  • Some models have a sensor head that can be easily damaged by human touch or other objects.


Logging level sensors

Cost-effective and reliable, compact groundwater logging sensors like the Van Essen Mini-Diver provide accurate and reliable long-term measurements of water levels, temperature, and conductivity—essential data needed for effective water resource management, environmental remediation, mine dewatering, and slope stability.

All Diver sensors have a 3 year warranty, up to 10 years battery life, and can be used from 300 m below to 5000 m above sea level.

We offer additional Diver sensors and other logging sensors.


Non-contact sensors

Both ultrasonic and sonic level instruments operate on the basic principle of using sound waves to determine fluid level. The frequency range for ultrasonic methods is ~20-200 kHz, and sonic types use a frequency of 10 kHz. A transducer directs sound waves downward in bursts onto the surface of the water. Echoes of these waves return to the transducer, which performs calculations to convert the distance of wave travel into a measure of height, and therefore water level.

Applications

  • Water level measurement with the sensor attached to a bridge or structure directly over the water.
  • Flood applications to avoid damage from debris flow

Advantages

  • Easy installation on a bridge or structure over the water.
  • Reduces the problem of sensor fouling or corrosion. Also potential damage from debris is reduced.

Limitations

  • The speed of sound through air varies with the air’s temperature. The transducer may contain a temperature sensor to compensate for changes in operating temperature. However, this only takes into account the temperature at the sensor, which may be different as the sound wave approaches the water
  • Debris, extreme turbulence or wave action of the water can cause fluctuating readings. Use of a damping adjustment in the instrument or a response delay may help overcome this problem.
  • Maximum distance to the water level surface is typically 30 feet or less.
  • Limited usage in shallow streams or in streams with very high velocities with minimum depth requirements.
  • Very high concentrations of fine sediment in suspension can scatter and absorb the sonic pulse, preventing reflection of a detectable echo.
  • Ultrasonics typically require more power than other water level sensors.
  • Build-up on the sensor head, even simple condensation, can cause problems with the sensor's operation.


Bubblers

Bubbler systems like the OTT CBS are hydrostatic pressure sensors that are ideally suited for accurate liquid and water level measurement, especially in industrial process systems.


Encoders / floats

A shaft encoder like the Stevens PAT is an electro-mechanical device used to convert the angular position of a shaft or axle to an analog or digital electrical signal. Part of the mechanical aspect of this device for level measurement utilizes a float and counter-weight attached to a line or tape placed around a pulley attached to the encoder’s shaft.

As the level changes, the float moves up and down and, thereby, rotating the pulley and the attached shaft—generating an electronic wave form for both rotating direction and amount. By converting shaft rotation into electronic signals, encoders are used to electronically monitor the position of a rotating shaft. There are two main types of encoders for liquid level measurements: absolute and incremental.

Absolute encoders provide a binary “word” for each position. Each bit requires a separate optical channel. The resolution is equal to the number of output bits. Absolute encoders constantly retain the correct position for one revolution. Therefore, the main advantage is that the output signal is not affected by a power shut-off. When power returns the encoder recognizes what position it is in based on the voltage measurement reference. Whereas incremental measurements rely on a referenced position pointer. Therefore, if power is shut off to an incremental encoder, the reference is lost and incremental pointer resets to zero.

Incremental (relative) encoders provide a contact or pulse for each increment of shaft movement. Usually this consists of two optical quadrature channels to enable the determination of the direction of rotation. The incremental encoder has a lower cost than the absolute encoder due to the limited number of channels, and the encoded position is not limited in revolutions.

Advantages

  • Since many older sites were designed for mechanical float operated measurement, encoders are easily adapted to existing float gear and gaging system.
  • Float-operated systems are easy to understand and troubleshoot.
  • Most encoders offer good temperature stability.
  • Various electronic technologies can be used including digital incremental and digital absolute (encoders); analog absolute (potentiometers and linear variable differential transformers); or digital absolute (synchros).
  • Float is protected in a stilling well and sensor is not in direct contact with the water. Therefore the risk of damage is low from debris flow or fouling.
  • Highly accurate with large-sized floats.

Limitations

  • Requires a stilling well to assure stability and reliability of the float-operating system.
  • Rapid changes in water level may result in the cable / tape line becoming disengaged from the float-operating sensor’s pulley.


Staff Gages

Staff gages provides a quick and easy visual indicator of water level. Made with a durable baked-on porcelain enamel finish on a metal plate. Stevens was the company who originally designed and introduced the staff gage measurement styles used by the water resource market.

Stevens is one of the leading designers and providers of custom staff gages. Custom staff gages are for non-standard sizes, slopes or flow measurements or for other unique mounting angles that a site may require for a easy visual measurement.


Contact Meter

Our contact meter is an ideal device for quick, portable measurement of bore holes, wells, reservoirs, and other applications where liquid level depth is needed. The probe is simply fed down and when it reaches liquid the light on the front of the unit illuminates. Depth can then be read from the easy-to-read white tape.

Stevens offers a range of multi-parameter sensors that provide a choice of water quality parameters to meet your unique monitoring needs.

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pH

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Depth (pressure)

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Chlorophyll a

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Blue-green algae

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Rhodamine WT

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Total dissolved gas

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Ion-Selective Electrodes (Ammonia/Ammonium, Nitrate, Chloride)

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Sunlight intensity

What's the Easiest and Quickest Way to Start Collecting Data and Access it Anywhere?

The Answer's in the Cloud.

eTracker is a cellular modem and "virtual" cloud-based data logger in one (meaning you don't need to install a separate data logger). Simply connect your sensor and a power source to eTracker and you're done. Configure (or reconfigure) anytime from any Internet-connected device, and use Stevens-Connect to retrieve your data, or forward it to your favorite software system.