Leveltrol calibration procedure

Calibration of Leveltrol in the Field

1. Preparation:

   • Close both primary isolation valves.
   • Drain the liquid inside the chamber.

2. Zero Adjustment:

   • Adjust the zero to get a 0% output.

3. Setup:

   • Connect a transparent PVC tube to the drain point as per hookup instructions.
   • Fill the tube to the center of the top flange.

4. Span Adjustment:

   • Adjust the specific gravity or span adjustment (for electronic leveltrol).

5. Check Linearity:

   • Fill up to 50% level and check linearity of output.

Calibration of Interface Level Control

• Interface leveltrol deals with two liquids of different specific gravities.

1. Zero Level (0%): When full of lighter liquid
   [ \text{Zero % level} = H \times d ]

   • (H): Displacer length
   • (d): Specific gravity of lighter liquid

2. Full Level (100%): When full of heavier liquid
   [ 100% \text{ level} = H \times D ]

   • (D): Specific gravity of heavier liquid

3. Calibration with Water:

   • Fill to (H \times d) level with water and adjust zero.
   • Fill to (H \times D) level with water and adjust span (specific gravity).
   • Check linearity.

Weight Test Calibration of Leveltrol

1. Remove the displacer from the torque arm.
2. Apply an equivalent weight on the torque arm equal to the displacer weight to adjust zero output.
3. For Span:
   
   • Volume (V = \pi r^2 h)
   • Loss in weight = Weight of float – (Volume × density of liquid)
   • Span weight = Weight of float – Loss in weight
4. Apply weight equal to Span weight on torque arm and adjust span to get 100% output.
5. Check linearity by applying average of the two weights.

Common Issues

• If displacer falls down while in line: Output will be at maximum.
• If displacer has a hole: Output will be at minimum.

Use of Suppression and Elevation

• Applied in level measurement when:
  1. Transmitters are not mounted at the same level.
  2. Wet leg is present (condensable vapors in the impulse line).

Limitations of Leveltrol

• Cannot be used for displacer lengths greater than 72 inches.

Commissioning a Differential Pressure (D.P.) Transmitter in a Pressurized Vessel

1. Close both isolation valves.
2. Vent the High Pressure (H.P.) side.
3. Fill the transmitter with sealing liquid.
4. Open the Low Pressure (L.P.) side vent valve.
5. Adjust zero using the suppression spring.
6. Close the L.P. vent valve.
7. Open both isolation valves.

Checking Zero of a Level D.P. Transmitter While Inline

1. Close both isolation valves.
2. Open vent valves on L.P. leg and drain H.P. leg.
3. Check and adjust zero if necessary.

Zero Suppression:

• Used when the transmitter is installed below the tank’s zero level.
• Because the transmitter senses additional hydrostatic pressure from the liquid column above it, it reads a pressure even when the tank is empty.
• Zero suppression adjusts the output to ignore this extra pressure, ensuring the transmitter outputs the correct minimum signal (usually 4 mA) when the tank is actually empty.

Zero Elevation:

• Used when the transmitter is installed above the tank’s zero level, or when a wet leg (a liquid-filled capillary line) is used on the low-pressure side.
• In this case, the transmitter senses less pressure than the actual level, so the zero point must be “elevated” (offset upward) to ensure the instrument reads zero level correctly.
• This adjustment ensures the transmitter outputs the correct minimum signal when the tank level is truly at zero.

Working Principle of an Enraf Level Gauge

• Uses a servo-powered null-balance technique with a displacer as a continuous level-sensing element.
• The displacer (denser than the measured liquid) is suspended by a wire attached to a drum.
• A two-phase servo motor controlled by a capacitive balance system winds or unwinds the wire to balance the tension against the buoyant force on the displacer.
• Capacitive sensors detect changes in level by measuring differences in capacitance caused by the movement of a sensing rod.
• An electronic circuit detects and integrates these changes.
• The servomotor’s rotation alters a voltage pattern transmitted to a remote indicator, which drives a counter to display the level variation continuously