We have already demonstrated in several projects that at eguana we are not only familiar with software, but also hardware. We want to present one of these solutions today: the eguana.Flowmeter.
In injection technology, it is essential to record the current flow rate, because on the one hand this is an important quality parameter (mixing ratios, reaction of the subsoil, etc.) and on the other hand it can also be used for billing.
For example, think of toothpaste with stripes: the white stripe contains the cleaning solution, the blue stripe creates foam and a pleasant freshness aroma. In our example, the toothpaste does not come from a tube – it is automatically sprayed into strips from two tubes on the toothbrush. Ideally, the same pressure is exerted on both tubes and we have the perfect toothpaste strip. But what if one tube is pressed harder than the other? And suddenly our stripe is almost only blue, and the excess of freshness almost freezes our mouths – without really cleaning.
We face similar quality problems in injection technology, only that a different mixing ratio can mean that the desired sealing success is no longer given. Various flow sensors are used to monitor the flows, but none of them is right.
For example, the relatively simple stroke counter: Each stroke of the pump delivers a certain volume; The total volume delivered, and the respective flow rate can then be calculated from the number of strokes. All good, but too imprecise, especially with small quantities, since even the smallest deviations can influence the properties of the pressed material (e.g. with 2-component systems) and billing quantities.
Or the ultrasonic flow meter (ultrasonic waves are emitted into the flowing medium; the transit time, phase shift and frequency difference between the transmitted and the received wave determine the flow velocity and the volume flow is calculated from this) or the Coriolis mass flow meter (this method is based on the Coriolis principle, information for everyone who would like to know more about it can be found here). Both devices allow very precise measurements and in the case of the Coriolis, the measurement of other parameters. Due to the high acquisition costs and the limited suitability for use in harsh environments, they are not necessarily suitable for the construction site.
… better …
That’s why magnetic-inductive flow meters (MID) are generally used, which are available in very robust designs and are therefore ideally suited to the conditions on the construction sites. A magnetic field induces voltage in the flow and converts it into flow velocity. MID do not need any moving parts, which is why they do not wear out. Sounds pretty good so far, right? MID, however, also have disadvantages – in fact they rely on the fact that the material flowing through has a minimum conductivity. This is the case with cement (roughly a mixture of concrete balls and water), but not with all chemical injectables. Furthermore, there is a build-up, which can lead to a reduction in the measurement cross-section and thus incorrect measurement results. I.e. the MID must also be regularly serviced accordingly.
In the case of polyurethanes, for example, which consist of two components and are combined at the mouth of the borehole using a mixing head, the monitoring of the flow rates of both components is crucial. Deviations of the speeds from one another, for whatever reason, lead to a change in the mixing ratio and thus to different properties, such as viscosity, curing time, or others.
With such chemical two-component systems, paddle wheel sensors are usually used, which are constructed similar to a water wheel. The volume flow drives the wheel via blades. Magnetic scanning generates electrical impulses (to put it simply: how often does the impeller or its fins pass the measuring point?). The frequency of the pulses changes in proportion to the rotational speed and thus to the flow speed (more flow -> faster rotational speed -> more pulses). The quantity delivered per pulse can be determined based on the design of the sensors. They follow the same principle as the piston stroke count, but with a much better measurement resolution, which can be accurate to 2 ml / pulse.
Since not all controls are able to record the flow rate via pulse inputs and only specially developed controls also take the deviations of the two components into account, we have developed the eguana.Flowmeter, which extends the paddlewheel sensors by exactly this point.
The tasks are simply summarized:
- Measuring of the impulses
- Calculate the current flow rate of both components and the total flow rate
- Calculate the deviation of the quantities delivered between the two components
- Generation of a constant current which is proportional to the total flow rate and which is read by the controller via a current loop
- Generation of specific impulses which are used by the control for quantity acquisition
- Optical output of the current status via a signal light (pumping process active / inactive, deviation OK / problem)
- Output of the flow rates, the pumped quantity and the deviation on a display
Since every paddle wheel sensor is subject to manufacturing tolerances, there is a calibration mode to determine and save the quantity per pulse.
In addition, the device must be able to withstand the harsh conditions of construction sites and be compatible with different controls. Compatibility could be ensured by orienting ourselves on the output signals of common MID. These measuring devices also generate 100 ml pulses to encode the total quantity and transmit the current flow rate via a 4-20 mA current loop. This means that the device generates a constant current which is proportional to the flow rate. Current loops are used because the influence of the signal lines is irrelevant. Line breaks can be easily identified. Since even a measuring signal of 0 l / min is coded with 4mA, a signal always arrives at the receiver. If this is not the case, there must be a technical problem with the sensor, the power supply or the connection.
Our FLOWMETER is already being used successfully. We are making another important contribution to quality assurance and digitisation of construction sites. For the first time, injections of this type can be optimally monitored, and the quality can be demonstrated during execution. Our little box is pretty powerful. And once again, the iguana proves that with will and adaptability a “That´s not possible” is followed by a “Very well with us!”.
Credit Titelbild: Bru-nO auf Pixabay