Standard measuring instruments
Deltares designs and builds instrumentation for flow measurements of waves, water levels, sediment concentrations and bathymetry. We use these instruments in our research facilities as well as in field studies in rivers, coastal areas and estuaries. Because of this, we know that our instruments are robust, accurate and easy to use. Our instruments are always calibrated before use.
Programmable electromagnetic liquid velocity meter (pEMS)
The electromagnetic velocity meter measures bi-directional water velocity in two perpendicular directions. The measurement principle is based on conductive liquid moving through a magnetic field. The magnetic field is induced by electrical current in a small coil inside the body of the probe. Two pairs of diametrically opposed platinum electrodes sense the induced voltages produced by the flow past the probe. The probe has been designed in such a way that these voltages are proportional to the liquid velocity parallel to the plane of the electrodes.
Applications
Specific applications where the electromagnetic liquid velocity meter can be used include:
- laboratory research
- engineering studies
- open channel stream gauging
- slurries and sludge transport
- environmental and hydrological measurements
- sedimentation and filtration processes
- flow monitoring under surge conditions
Standard probes
There are two standard probes available. The E30 type probe is especially suitable for physical model studies and laboratory research due to its smaller probe size. The E40 type probe has a larger probe size and is therefore more robust. Furthermore, the E40 type probe can be fully submerged in liquid, as opposed to the E30 type probe. Next to these two standard probes, special probes (e.g. cranked) can be made to suit specific applications. As described above, the probes measure the liquid velocity using a magnetic field beneath the probe. This magnetic field should not be disturbed. The probes have to be connected to a control unit.
More information on liquid velocity measurements: pEMS
Wave height measurements (WHM)
The wave height and direction meter features simultaneous measurement of both wave height and orbital velocity by combining two probes at the same spot. One probe measures wave height, the other probe measures orbital velocity. The main purpose of this instrument is to measure wave direction and directional spreading. Each probe is connected to a dedicated control unit by a power signal cable. Both control units are mounted in the same universal carrying case (UCC). Output signals for surface elevation and x- and y-velocities are analogue.
Applications
The wave height and direction meter are primarily used in (3D-wave) basins for tests and experiments on:
- wave penetration in harbours
- performance of breakwaters and dikes
- coastal protection
- load and stability of offshore structures
- determination of reflected waves
This instrument is also used in flumes to make distinction between incident and reflected waves.
Wave height meter
The wave height meter is constructed of two parallel stainless-steel rods, mounted underneath a small box. This box contains electronics for sensor excitation, signal detection, amplification and galvanic isolation. The rods act as the electrodes of an electric conduction meter. A platinum reference electrode is included to compensate the surface elevation measurement for the effect of varying electrical conductivity of the fluid. The analogue output signal is linearly proportional to the water level between the sensor rods.
More information on wave height measurements WHM
Measuring sediment concentrations
- Sediment optical - low concentrations OSLIM / FOSLIM / OPCON
- Sediment acoustic - average concentration UHCM
- Sediment conductivity - high concentration
The OSLIM optical silt measuring system
The OSLIM optical silt measuring system is an instrument to measure concentrations of suspended particles. The measuring principle is based on the attenuation of the intensity of light passing through the measuring volume. The light is absorbed and scattered on suspended silt particles. The output is presented as an analogue voltage.
The OSLIM system consists of a probe and a control unit. The control unit provides the system with power, controls, and switches for setting the zero, span, out-of-range detection and analogue output. The particle suspension is to pass the OSLIM probe, e.g. by pumping.
Applications
- Analysis of suspended sediment samples
- Monitoring of suspended matter in liquids
FOSLIM optical silt measuring system
The FOSLIM optical silt measuring system is an instrument designed to measure concentrations of suspended particles. The measuring principle is based on the attenuation of light passing through the measuring volume. The light is absorbed and scattered on suspended silt particles. The output is presented as an analogue voltage.
The FOSLIM system comprises a probe and a control unit (the same model as used together with the OSLIM instrument). The control unit provides the system with power, controls and switches for setting the zero, span, out-of-range detection and analogue output. The FOSLIM probe is to be immersed in the particle suspension.
The measuring volume resides between two optical fibre tips. The measuring volume is illuminated by the one optical fibre and received by the other fibre; the receiving fibre is aligned ‘looking’ towards the transmitting fibre. The distance between the two opposing fibres is adjustable by the operator to adapt the instrument to a specific measuring range.
Applications
- Silt transport studies
- Mud concentration profiling
OPCON
The OPCON is an instrument specifically for measurement of suspended particle concentration in the field of hydraulic sediment transport investigations. Together with the OPCON control-unit it enables detailed non-sampling measurements with negligible process disturbances. Depending on the characteristics of the particles the OPCON can also supply data about the size of the particles.
Applications
- hydraulic research
- engineering studies
- industrial processes
- environmental and hydrological measurements
Ultrasonic High Concentration Meter (UHCM)
The measuring principle of the UHCM is based upon attenuation of ultrasonic energy passing through a suspension of sediment particles. Its measuring range depends, to some extent, upon the kind of the particles. The UHCM is intended for high concentrations of particle suspensions of clay, silt, sand, mud, sludge and similar. The analogue output signal is proportional to sediment concentration.
The UHCM-system comprises:
- an acoustic probe with opposing transmitter and receiver elements
- a UCC instrument housing and acting as system power supply
- a UHCM control-unit with:
- controls
- logarithmic amplifier
- LCD-display unit
- analogue output
Applications
- laboratory research
- bed sediment of rivers and harbours
- slurries (cement, clay, etc.) UHCM control unit
- environmental investigations and studies
- concentrated suspensions in the food-industry
- sludge (water treatment, sewage, etc.)
Conductivity type Concentration Meter
The conductivity type concentration meter (CCM) system is an instrument to measure the concentration of sand-water suspensions. The measuring principle is based on the conductivity change of a sand-water mixture due to change of the amount of suspended sediment present in the measuring area. The conductivity of the fluid should differ from the conductivity of the particles. By a second (slave) unit the conductivity of the particle free fluid can be continuously monitored and compensated for.
The CCM system consists of a probe and a CCM control unit. The control unit provides the power, controls and switches. On the control unit settings for the type of measurement (concentration or conductivity), the range, the span, the LCD display unit and the analogue output can be adjusted. The output is presented as an actual value on the LCD display and as an analogue output voltage.
Applications
- Bed sediment settlement or erosion
- Dredging studies
- Concentration of suspensions in the food industry
Wave research
Hard- and software
Delft-Measure is a data acquisition system, comprising both hardware and software. It is configured for operation in a PC environment under Windows. The standard version is primarily intended to acquire data of analogue instruments. On request digital instruments, e.g. counters and serial devices can also be supported. The operator controls Delft-Measure via a graphical user interface.
Essential functions like setup, data acquisition and performance monitoring are supported. While data acquisition is in progress, acquired data is graphically visualized in strip chart fashion and also displayed numerically. Most importantly, the data values are recorded in file (ASCII or binary).
More information on data acquisition - Delft Measure
Measurement campaigns
We also advise on setting up measurement campaigns. This includes advice on which instruments are needed for a specific measurement but also whether it is possible to adapt the instruments to the situation. Due to our own work in the field and research facilities, we now have a lot of experience with this.
An example is the meters adapted for the Delta flume, which are equipped with measuring electrodes (wires) made of a titanium alloy with optimal electrical and mechanical properties.
