The Wireless Level Measurement Transmitter and Receiver perform liquid level measurement and sends the data by radio signal from the Transmitter to the Receiver. The wetwell part of the product consists of two parts, connected by a cable; the Transmitter and the Pressure Sensor. The Transmitter is suspended above the liquid, and the Pressure Sensor is submerged in the liquid near the bottom of the tank.
The Transmitter transmits updated level data and battery condition data once every second. To conserve battery power, most of the circuitry is powered down and asleep between updates. After being asleep, the Transmitter wakes up, powers up the Pressure Sensor, checks the level, checks the condition of the battery, transmits the new data to the Receiver, and then goes back to sleep. We estimate that the transmitter battery life to be fifteen years.
The Pressure Sensor converts the pressure exerted by the liquid into an analog voltage signal that represents the liquid level. The Transmitter and sensor are a sealed unit, and measure Absolute Pressure. Atmospheric Pressure is measured in the Receiver, and is used to subtract from the absolute value to provide the Gauge Pressure representing the wetwell level.
The pressure sensor contains a stainless steel diaphragm and silicone oil fill is provided to isolate and protect the pressure sensor from the liquid being measured. The weight of the Pressure Sensor acts to reduce its movement when placed in a moving liquid. A Strength Cord in the cable provides ample support for its weight. In applications where strong currents may be present, the 1/2” NPT fitting on top may be used to mount it in a fixed position.
The Pressure Sensor and the Transmitter come connected together tested and calibrated as a unit and are calibrated to read levels between 0.0 feet and 34.6 feet, providing a 16 bit number to the Receiver that represents the measured level. Calibration of the 4-20mA analog output, provided by the Transducer Receiver, is done using the Zero and Span potentiometers on the Receiver. Zero and Span potentiometers are provided for field calibration of the analog 4-20mA output. The Span may be adjusted for 20mA @ 11.5 feet/H2O, 20mA @ 23.1 feet/H2O, or 20mA @ 34.6 feet/H2O.
The Wireless Transducer Receiver reads the liquid level information in the radio signal from the nearby Wireless Transducer Transmitter and provides an analog 4-20mA output and SCADA register data that represents the liquid level being monitored. For applications where the Transmitter and Receiver Antenna have line of site, reliable communication can be maintained at distances up to 125 feet.
The Receiver provides three levels of Radio Link Quality indication. High, which indicates strong error free communication. Low, which indicates less than ideal communication. Lost, which indicates no communication with the Transmitter. The Battery Low indication is provided to indicate the condition of the battery in the Transmitter. Connecting the RS-232 serial port (or optional Ethernet Port) to a SCADA system allows the liquid level to be monitored remotely.
When we were down at MPE last month, another cool product John shared with us was the new Wireless Level Measurement Transmitter and Receiver platform. We're really excited for the applications where it's not feasible to run wire to the transducer, but level monitoring is still necessary.
For all the details, here's the MPE press release on it. Bolded parts are my highlights.