Transmitters convert the measurement parameter (rotation, resistance, etc.) to an electrical signal for transmission over an instrumentation field bus or communications loop. Most transmitters use an incremental or absolute encoder with either brush, optical, magnetic or the latest capacitive sensors.
Incremental encoders count steps up or down to find level and then store the information in memory. A power loss can causes the transmitter to forget where it is, so recalibration or a battery backup may be required. Absolute encoders count the absolute position on the encoder disc to find level. After a power loss the encoder knows where it is, so no battery backup and no recalibration is required.
Brush sensors make contact with the encoder disc causing the encoder to wear down over time and brushes may “feather”, which will affect the accuracy or reading. Brush sensors need replacing every 5-8 years. Optical sensors, either linear or reflective, do not make contact with the encoder disc. Sunlight may affect calibration (except with infrared sensors) and photo-etched (painted) discs may fade, affecting the reliability and accuracy of the reading. Varec’s 2920 FTT uses the latest capacitive sensors with gold plated etched discs to provide maintenance free operation with the most accurate output to on the market to date.
Temperature Measurement Integration
Temperature sensors connected to the transmitter allow the inventory system, such as FuelsManager®, to calculate volumes that are temperature corrected. Spot temperature sensors are appropriate for float & tape tank gauging, while average temperature devices are generally associated with radar or servo tank gauges due to the increased accuracy obtained from the level device.