How Does an Electrolytic Sensor Work?

Electrolytic Sensor Technology

For static applications, electrolytic is the highest accuracy and most repeatable technology. The Electrolytic tilt sensors have no mechanical moving parts to break or wear out, and because tilt is referenced to gravity, they can be installed anywhere without the need for complicated levers or fixtures.

The words tiltmeter, inclinometer, and clinometer all refer to an inertially referenced device that measures angular rotation with respect to a vertical gravity vector, the most stable of all external references. At Jewell Instruments, we denote our higher precision geo instruments as tiltmeters. We use the name clinometer for our general-purpose 900-Series products.  Our Electrolytic Sensor technology is an integral part of our Geo Products used in both Geophysical and Geotechnical markets for a range of applications.

All Jewell tiltmeters and clinometers include full signal conditioning electronics that produce stable output signals over a wide range of input voltages. This important feature means you can be confident that our measurements represent actual movement and not power supply variations. The high-level voltage, current, and serial outputs provided by our electronics assure reliable data delivery over long cables and wireless data links. As a bonus, all of our tiltmeters include temperature measurement in their output.

We divide our tiltmeters into four different Series based on measurement resolution and angular range: Economical, High Precision, Ultra Precision, and Mini Tilt Sensors and Signal Conditioners. Certain instruments report resolution in microradians or even nanoradians: a reflection of their high level of sensitivity.

How do they work?

Jewell Instruments tiltmeters and clinometers each contain one or more electrolytic tilt sensors. These sensors consist of a sealed glass or alumina vial that is partially filled with electrolytic liquid. This conductive fluid covers three or five internal electrodes according to the sensor type. The sensor’s operation is based on the fundamental principle that an enclosed bubble, suspended in a liquid, always orients itself perpendicular to the vertical gravity vector. Traditional applications of this phenomenon include the humble carpenter’s level and spirit levels on surveyor’s transits and navigational sextants.

Electrolytic tilt sensors offer amazing performance in a small and affordable package. Dynamic range is the maximum measurement range divided by the smallest angle that can be detected with the sensor. Some of our sensors achieve a dynamic range greater than 120 dB (>1,000,000:1).

Jewell Instruments tiltmeters operate electrolytic tilt sensors as AC voltage dividers (potentiometers). The tiltmeter’s electronic circuitry creates a balanced AC signal that is applied differentially to the two excitation electrodes. The amplitude and phase of the output signal, measured at the pickup electrode, indicate the magnitude and direction of tilt movement.

When the sensor is level, the conductive liquid covers an equal area on each excitation electrode; the AC resistances, R1 and R2, between the excitation electrodes and the pickup electrode are equal. When the sensor is tilted, however, the liquid covers more of one excitation electrode than the other and R1 and R2 are not equal.

Tilt sensors can also be operated as the active half of a Wheatstone bridge. The Wheatstone bridge circuit is mainly used for nulling (leveling) applications. Regardless of which type of circuit is used, only AC excitation may be applied to the sensor. Direct current damages the sensor by causing plating of the electrodes.

Our uniaxial tiltmeters use a single tilt sensor. Biaxial tiltmeters in our 500700 and 800-Series use two tilt sensors, oriented orthogonally. Our 900-Series biaxial clinometers use an electrolytic tilt sensor with five electrodes, arranged in the pattern of a cross. In this instance, biaxial tilt measurements are made by alternately exciting orthogonal pairs of electrodes.

How Accurate are our Electrolytic sensors?

Electrolytic sensors are some of the most sensitive in their market with a resolution as fine as 2.5 nanoradians. What is a nanoradian? Let’s say you have a beam that stretches from San Francisco to New York City (2500 miles). If you raise one end by 4 mm, about an eighth of an inch, you have tilted it by a nanoradian.




The main advantages of the electrolytic technology are:

  • Extremely repeatable
  • Incredible resolution as fine as 2.5 nanoradians
  • Absolute gravity reference, the most stable of all external references
  • No power-on errors
  • No mechanical elements that can break or wear out
  • Low Thermal drift

While some models are built to survive the elements, the added enclosure makes for a larger footprint.

These sensors have a low-frequency response, which means they should be mounted to be stationary and upright to make small, gradual measurements, which is great for monitoring the activity of a structure or embankment. Some other special considerations are:

  • Low frequency response (intended for stationary measurements only)
  • Generally larger footprint
  • Must be mounted upright.
  • Not used for measuring acceleration
  • Only recommended for static geophysical and geotechnical applications without any vibration or shock

Will require some settling time after sudden movement occurs.

Product Selection

 Resolution (up to)Max Range (up to)
Miniature & SC755/756 and others<0.1 μradian±80°
Ultra-Precision500 Series<5 nanoradian± 300 µrad
600 Series<2.5 nanoradian±0.235º
700/750 * Series<0.1 µrad (0.02 arcsec)± 8 degrees
High-Precision800 Series<1 µrad (0.2 arcsec)±70  degrees
Economical900/850*/875* Series<100 µrad (20 arcsec)± 50 degrees
*Note: the 750 uses a different technology called Force-balanced.
                The 850 and 875 uses a different technology called MEMS.

900 Series

OEM, factory & industrial, pitch and roll applications

The Clinometer A904 series is an economical solution in a rugged NEMA 4X (IP65) enclosure. It incorporates a high-precision electrolytic tilt transducer as the internal sensing element, offering unrivaled resolution and long-term stability. Measured angular movement is referenced to the unchanging vertical gravity vector, eliminating the time and expense of locating an external datum. It is ideal for a wide variety of engineering projects including structural behavior testing, monitoring of foundation conditions, surveillance of natural and manmade structures, and machine positioning and control.

The Clinometer C904 is loop-powered. No separate power supply is required to power your tiltmeter, as it takes its power from the current loop. A temperature sensor also is included in your Clinometer C904. Output is a DC current proportional to temperature in degrees Celsius.

The biaxial model MD900-T is an economical digital clinometer with powerful firmware features, designed for a variety of industrial and scientific applications, such as industrial pitch and roll measurement, marine piling, dredging and construction systems, platform leveling, geotechnical monitoring and more. User programmable settings include AUTO-zero (tare), baud and output rate, sample averaging, and more. Available serial interfaces are RS-232 or RS-422 (RS-485 full duplex). Factory calibration values are stored in non-volatile memory. A liquid-filled electrolytic transducer comprises the sensing element and is excited and read by stable, low-noise electronics. The clinometer is housed in an easily mountable enclosure and provides an RS-232 or RS-422 serial interface.

800 Series

Geotechnical, slope stability, precision measurement & control

The Model 801 Tuff Tilt Uniaxial and Biaxial Tiltmeters are excellent sensors for a wide variety of monitoring and measurement applications. Model 801 tiltmeters are available in high-gain (±0.5 deg range), standard (±3 deg range) and wide-angle (±50 deg range) versions. Each of these versions is produced in both longitudinal, transverse, and biaxial tilt styles. The Model 802 DeepWater is a precision tiltmeter designed for underwater tilt measurements and other applications involving high external pressures. Model 802 offers unrivaled sensitivity and long-term stability under these demanding conditions. The 316 stainless steel housing encloses stable, low-noise electronics and an electrolytic tilt sensor, which is the internal sensing element. Measured angular movement is referenced to the unchanging vertical gravity vector, eliminating the time and expense of locating an external datum. DeepWater tiltmeters are an excellent choice for monitoring the behavior of underwater structures, such as dams, oil platforms and pipelines; measuring the rotational movement of underwater machinery; and tracking the pitch and roll of marine vessels. We also offer a shallow-water 820 series for use in fresh & salt water application. Its enclosure is made out of 316 stainless steel and rated to 200 meters (656.2 ft) waterproof for advanced protection from the elements.

700 Series

Geotechnical, slope stability, precision measurement & control

Our 700-Series Platform and Surface Mount Tiltmeters are dual-axis, analog output tiltmeters, designed for high-sensitivity, low power consumption, durability, and reliability under rugged field conditions. Suitable for geotechnical and geophysical projects in remote locations, they will also provide years of trouble-free service in industrial and laboratory applications. They are used worldwide for monitoring earth and structural deformation at dam sites, mines, volcanoes, power plants, engineering and scientific laboratories, bridges, highways, and many other industrial and scientific facilities. Platform and surface mount tiltmeters are essentially the same and consist of an aluminum or stainless-steel base plate, aluminum or stainless-steel cover (dome), sensors, PC board, connectors, and switches. They differ in that platform tiltmeters have adjustable legs that are used for leveling the tiltmeters on any hard horizontal surface. In contrast, surface mount tiltmeters have holes in the base plate and are mounted over threaded studs embedded in the measurement surface. Nuts are used to adjust the position of surface mount tiltmeters and to stably lock the tiltmeter in place for long-term measurements.

The D711 is a precision biaxial digital tiltmeter packaged in a weatherproof housing. The high-gain version, Model D711-A, has the greatest sensitivity and an angular range of ±0.5 degree. The mid-range version, Model D711-B, has a much greater angular range (±5 degrees), but is less sensitive. Some typical applications include precise alignment of telescopes, antennae, and air frames; monitoring of structures and foundations; monitoring of volcanoes, and all jobs that call for precision measurements under demanding operating conditions. The Tiltmeter is available with either RS232 or RS485 digital output. RS232 is typically limited to cable lengths less than 15 meters (49.2 feet). The RS485 output of the Tiltmeter, which is functionally equivalent to RS422 output, can drive cable lengths greater than 1000 meter (3,231 feet). Model D711 bolts or clamps to any surface and can be used in areas of heavy traffic or vibration.

600 & 500– Series

Geophysical research, high precision metrology

The 603 High-Precision Platform-Mount Tiltmeters are dual-axis, analog output tiltmeters, designed for high-sensitivity, low power consumption, durability. Suitable for geotechnical and geophysical projects in remote locations, they will also provide years of trouble-free service in industrial and laboratory applications. The tiltmeter is constructed with a painted white aluminum cover (dome), stainless steel base plate, electrolytic tilt sensors, PC board, connectors, and switches. It has two adjustable worm gear legs making the tiltmeter easy to level when placed on a hard horizontal surface. The switches allow the tiltmeter to change between its gain settings and enable additional passive filtering.

The LILY Self-Leveling Borehole Tiltmeter is designed for volcanic and tectonic research and for monitoring of hydraulic fracturing and other subsurface processes in the energy and mineral industries. LILY is the culmination of over 35 years of experience in the fields of instrumentation and geophysics by engineers and scientists. Its small diameter and high-pressure stainless-steel housing give it ruggedness and versatility for demanding field projects. The dual-axis tiltmeter senses angular movement in two orthogonal vertical planes using precision electrolytic tilt sensors. The digital electronics convert the tilt signals to easily recorded RS485 or RS232 data streams that contain tilt (2 channels), azimuth, temperature, serial number and time. Data output in NMEA 0183 format is a standard feature. The LILY tilt sensors can self-level on command through a range of ±10 degrees and have <5 nanoradians resolution over a dynamic range of ±330 microradians. LILY incorporates an innovative new design that achieves high mechanical stability, necessary for stable long-term measurements, at a much lower cost than was previously possible in instruments of this type.

Miniature Tilt Sensors & Signal Conditioners

Geophysics, antenna/radar position, high-precision Geotech

Our Miniature Tilt Sensors such as the 755 & 756 series are the most precise and repeatable commercial sensor for measuring gravity-referenced angular movements and are very low-profile. Miniature Tilt Sensor contains either one or two electrolytic tilt transducers, one for each orthogonal axis of rotation. Series 755 sensors contain high-gain (Type A) transducers that resolve angular changes smaller than 0.1 microradian over ±1 degree of arc. Series 756 sensors incorporate mid-range (Type B) transducers that resolve 1 microradian over ±10 degrees. We recommend that your sensor be operated with signal conditioning electronics supplied by Jewell Instruments LLC.

The model 781 Signal Conditioning Unit (SCU) is a compact module that may be used with all Jewell Instrument tilt sensors. Internal SCU electronics provide simultaneous excitation of two electrolytic tilt transducers and condition the returned signals into two analog DC voltages. The SCU provides both single-ended and differential outputs on each of its two tilt channels. You may thus select the output that is best suited for your application. The SCU also takes temperature readings from a National Semiconductor LM-35 temperature sensor, providing an analog output proportional to temperature. Temperature is provided as a single-ended output only.

Jewell Instruments’ instrumentation is used worldwide for measuring the behavior of dams, power plants, machinery, mines, bridges, buildings, tunnels, tanks, retaining walls, wells, landslides, volcanoes, and other natural and manmade structures. Please contact the factory for more information on these products.

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