The Surcharge Level transducer is a differential solid state type transducer with a stainless-steel diaphragm. The diaphragm is located about 4.5” below the top of the tubular mounting frame. The Surcharge Level transducer becomes operable before the water surface reaches the standard range ultrasonic level transducer dead band. The pressure transducer is differential and has an air tube for the atmospheric reference. If this air tube becomes blocked or restricted by moisture the Surcharge Level transducer will become a barometer and a thermometer drifting up and down with atmospheric pressure and temperature changes. A depleted desiccant is the most common cause of surcharge level drift. Desiccants should be inspected and replaced or recharged at all site visits. A site visit is suggested after surcharges that submerge the logger and desiccant assembly.
Flo-Ware reports surcharge level directly without considering the sensor height or offset. This means the surcharge level value in Flo-Ware or on the Flo-Station represents approximately the water depth above the sensor and not the total surcharge depth. To get the total depth in Flo-Ware the recorded surcharge level values must be added to the sensor offset - 4.5”. FSData handles surcharge level differently. In FSData surcharge level is handled just the same as it is in Flo-Ware as long as the Flo-Dar sensor is not in the surcharge condition. When a surcharge condition exists: surcharge level > trigger value (1”) or distance < switchover value (7”) and conductivity > trigger (50) FSData will add the sensor offset value - 4.5” to the surcharge level value. This allows for viewing small drifts around 0 when not in surcharge while reporting the true surcharge depth during surcharge conditions.