As with all interesting applications, we are faced with some constraints to work within.
In this application, we are working on placing level measuring instruments on relatively older tanks that have had their drawings misplaced and possess little or no references to their dimensions. Currently the liquid level of the tank is measured by using a dip tape with a strapping table. We do not have the exact distance from the nozzle position to the bottom of the tank.
As the tank is still in service, we are do not want to remove the product from the tank or modify the tank to fit in our instruments.
Also, no instrument cables or any type have been laid down from the control room to the tank.
Choosing the instrument type
Not removing the product from the tank or modifying it means that we will have to use a top-down measuring solution to determine the level.
A non-contact solution is also preferred because the tank will be used to contain different products and its physical properties may change, making the measuring instrument inaccurate.
Of the non-contact solutions, laser has the smallest footprint size and beam divergence angle. As the nozzle that we are able to use on this particular tank is very near the side of the tank, having a smaller beam divergence angle will mean lesser issues for us to tackle later (such as signal disruption by the tank walls).
Height: About 10.6 Meters
Process connection: 4 inch flange
Contains: Lubricants and mixtures
After placing this unit to test for a week and comparing the readings with the dip tape measurement, we realized that the instrument read almost the same as the dip tape at high levels but increasingly lesser compared to the dip tape at lower levels. This can be attributed to the angle of measurement of the laser being different from the angle of measurement of the dip tape. We have further narrowed the problem down to our flange adapter.
Working with the nozzles available meant that we were not given too many options and had to modify our equipment to fit the size of the nozzle available.
Our standard unit comes with a 2" flange process connection which we had to place an adapter on to fit the 4" flange we were given. Doing this caused some issues with the alignment as our adapter flange may not have a uniform height all round.
Below is an image of what could be wrong and the impact a small difference in measurement angle makes in the results.