Basics of Zero Suppression and Zero Elevation (Range Suppression and Range Elevation)
Head Pressure = (Density of Liquid) * Acceleration Gravity * Height
H1 = Distance from transmitter to upper tap H2 = Distance from transmitter to lower tap H3 = Distance from transmitter to measuring point
Range Suppression - If an instrument is mounted below a vessel,it senses a total head,but the head due to the distance from the instrument location to the bottom of the vessel does not represent level in the vessel. This head must be cancelled by a range suppression calibration,using the zero adjustment provided in the instrument.
Range Elevation - If an instrumented is mounted above a vessel,the distance from the instrument location to the zero level of the vessel must be added by a range elevation calibration,using the zero adjustment provided in the instrument.
Pressure and differential pressure transmitters are typical and all such instruments provide built in zero and span adjustment to provide range or zero elevation or zero suppression.
Once the zero calibration is complete for either suppression or elevation,the span adjustment provided in the instrument is used to calibrate the actual the actual range of level change measured in the vessel.