How to Commission a Tank ATG Level Gauge

Back to Blog

Set the Reference Height and Datum

An ATG reports level relative to a datum, so the first task is telling it where that datum is. Enter the gauge reference height, the fixed distance from the gauging reference point to the tank datum plate, exactly as certified, because the ATG uses it to convert its raw measurement into a level that can be compared with a manual gauge. A wrong reference height offsets every reading by that error and breaks the reconciliation with a hand dip, which is the whole point of an ATG in custody or inventory service.

Confirm which measurement the gauge takes, innage or outage, and that its sign convention matches the tank's gauging convention, since a servo or radar ATG can be set either way. The reference framework is the same one behind a manual gauge, built on the reference gauge height, and aligning the ATG to it is what lets the two agree. Record the entered reference height and datum on the commissioning sheet, because a later unexplained offset almost always traces back to one of these numbers.

Enter and Check the Strapping Table

Level is only half the job; the business wants volume, and the strapping table is what converts one to the other. Enter the tank calibration table, the certified level-to-volume relationship, into the gauging system, and check a few points by hand against the certificate to catch a transcription error. A tank is rarely a perfect cylinder, so the table accounts for its real shape, bulges, and internal deadwood, and interpolation between table entries handles intermediate levels. The concepts are covered in the gauge table interpolation and deadwood notes.

Confirm the table matches the current tank, because modifications, added heating coils, or a floating-roof correction change the volume relationship, and an out-of-date table quietly corrupts every inventory figure. Where the tank has a floating roof, ensure the roof correction is applied so the displaced volume of the roof is handled. The table should trace to a tank calibration certificate, and commissioning is the moment to confirm the loaded table and the certificate agree.

Configure and Prove the Alarm Points

An ATG usually carries the tank's high-level and overfill protection, so its alarm elevations are safety-relevant and must be set to the correct physical levels, not nominal ones. Enter the high, high-high, and overfill setpoints as the design specifies, and confirm they sit in the right order and at the right elevations relative to the tank's safe fill and overfill points. Where the overfill function is part of a protective system, its verification follows the site procedure for that system and involves the appropriate personnel, since it is a safety function.

Prove each alarm actually actuates. Where the gauge supports a simulated level or a test mode, drive the reading up through each setpoint and confirm the alarm annunciates and any associated action occurs, then confirm it clears on the way down. A configured alarm that was never proven is a common and dangerous gap, because the setpoint can be right in the configuration and still fail to reach the annunciator or the shutdown due to a mapping or wiring error downstream.

Verify Against a Manual Gauge

Prove the whole commissioning by reconciling with an independent manual dip on the same datum. Take a hand gauge, convert both it and the ATG to a common zero, and confirm they agree within the tolerance the service requires. Then confirm the ATG-derived volume matches the strapping table for that level. Agreement on both level and volume means the reference height, the datum, and the table are all consistent, which is the definition of a commissioned ATG.

Do the check at more than one level where practical, since a single point can hide a table or span issue that only shows elsewhere. Log the manual gauge, the ATG level, and the volumes together as the commissioning baseline. When the ATG feeds a monitoring history, later periodic dips overlaid on the continuous trend reveal any slow divergence, letting you catch a drifting sensor or a reference that shifted before it distorts an inventory reconciliation.

Avoid the Common Mistakes

The commissioning failures are reference and table failures, not sensor failures. A wrong gauge reference height offsets every reading and breaks reconciliation. A mistyped strapping table entry corrupts volume at specific levels. An out-of-date table that predates a tank modification quietly biases inventory. And alarm setpoints that were configured but never proven give false confidence in overfill protection. Check each reference against its certificate and prove each alarm before signing off.

Because an ATG produces a clean, authoritative-looking number, an error in its references hides well behind a plausible reading. Reconciling against a manual dip on a common datum is the check that exposes it, and building the logged dips into a monitoring history turns that reconciliation into an ongoing one. The trend catches slow reference drift; the periodic dip and the strapping certificate say whether the fault is the sensor, the datum, or the table.

Frequently Asked Questions