(originally published 01/30/12)
Blue Sphere was recently challenged to design and implement a level control system for a wastewater stream which contained large amounts of adhesive. The adhesive has a tendency to dry/set up upon tank walls, traditional float based level switches and everything else it comes in contact with. For this reason we needed to use an economical no-contact level sensor.
While there are many radar based transmitters on the market, most of the devices are costly. It would not be uncommon to pay more than $1,000 per sensor. Upon conducting a little research, Blue Sphere selected the Flow-line Ecopod DS-14 for use as a high level alarm switch. The DS-14 seems to provide sufficient functionality and economy. The units sell for around $350 each.
Blue Sphere personnel have utilized Flowline equipment in the past with poor results. Early Flowline model transmitters where difficult to commission in the field. The set points had to be measured off of a wall with a tape measure. Additionally, we found the structural integrity of the housings to be poor. The clips which held the lids on would break thus allowing water into the device.
However, Flowline appears to have engineered out those particular issues with the DS-14. The unit is small, watertight and rugged. Programming is accomplished via a laptop with a little FOB interface that only costs $50. We are excited to put this device to work in the field and report on its performance. Six of the DS-14 level switches are being installed and will be tied to a small customized PLC control system.
The DS-14 radar based level sensor was found to give false positive readings on tanks that were taller then the devices rated range. This was despite manufacturer literature stating that the device would fail with an open relay upon week signal return. However, we were pleased with the structural integrity of the device and the ease of use of the programming software. Blue Sphere had to replace three Echopod DS-14 with the larger transmitter DL-24. Two of the DL-24 transmitters have performed well to date on tanks with relatively low levels of turbulence. One was ultimately changed out and replaced by a Flowline LP-15 capacitance based sensor on a tank with a high level of turbulence.