By Bill Sholette
A recent trend in level measurement for lift station wet wells is radar technology. In the past, radar transmitters were considered too expensive for use in wet wells but recent developments in electronics have allowed for new offerings in the sub-$1,000 range.
Radar transmitters offer a number of advantages over traditional wet well level technologies. First, like the ultrasonic instrument, radar is a non-contact technology using the time-of-flight measurement principle. With radar, an electromagnetic pulse is directed to the surface of the material being measured. The energy is reflected by the dielectric property of the water. Similar to ultrasonic, the time taken to reach the water surface and the reflection to return are measured, providing a distance to the surface of the water, which is then used to calculate the level.
Along with the advantages of non-contact measurement, the transmission of electromagnetic energy is not affected by vapors or steam in the air space above the water, which is a decided advantage over ultrasonic level technology.
New radar antenna designs provide wetted parts of all Teflon with a concave surface. These concave antennas are designed to shed condensation buildup on the antenna face, preventing attenuation of the electromagnetic signal. In sewage wet well applications, the Teflon helps to prevent coatings from adhering to the antenna when water splashes solids.
Mapping It Out
One of the great advances in new radar units is the simplicity of commissioning and mapping. Accessing the setup program can be done via Bluetooth® and executed on a smart phone or tablet. This is a great advantage over older units that required commissioning through a push-button HMI interface or opening the housing and connecting a cable to a laptop with a modem.
In many cases the radar transmitter may be located in an installation that is difficult to access. This is particularly true of water and sewage wet wells where the radar may be inside a concrete vault. Trying to reach these units for access to the HMI or to connect a cable to a modem may require a confined-space permit. With Bluetooth, in most cases it is a simple matter of opening the manway.
New radar technology offers sophisticated mapping programs that allow the transmitter to ignore internal obstructions such as ladders, pump columns, cables and baffles. While these mapping programs are sophisticated, they are much easier to implement than previous mapping programs from even a few years ago.
Summary
There are a number of ways to measure the water level in lift station wet wells. Selecting the technology able to provide the most reliable level measurement with the least maintenance should be the goal. While traditional technologies such as submersible hydrostatic and ultrasonic instruments can provide a reliable measurement, the new lower-cost radar transmitters now available in the market should be considered for these applications. The advantages gained in performance and reliability along with the ease of commissioning are significant.
Bill Sholette is the level product business manager for Endress+Hauser. Learn more at www.yourlevelexperts.com/bluetooth-boundless.
