Centre Hole Load Cell Installation: Preparation & Troubleshooting

Encardio-rite model ELC-30S Centre hole load cell is a precision-engineered instrument used to measure tensile force in a ground anchor, rock bolt, cable or tie back. It is also used in the measurement of compressive load between structural members, i.e. tunnel supports or at the junction between a beam and the top of a pile strut.

Preparation of sensor before load cell installation

To give way to the six-pin terminal, remove the cable joint housing from the edge of the sensor. We only make use of four terminals. The active ones are marked with red, green, black, and white dots. Make sure to clean the terminals using a toothbrush.

NOTE: Make sure you’re not making use of acetone for cleaning the terminals as it may hamper the glass to metal seal. However, you can use acetone for other parts of the sensors.

Here’s how you can check if the sensors are working accurately.

1. Measure the resistance using a digital multi-meter. It should be 770 Ohm ± 5 % between red/black terminals and 700 Ohm ± 1 % between green/white terminals.
2. On the other hand, the resistance between the outer casing and any lead should be greater than 500 M Ohm.
3. Measure the zero balance of load cell using a portable digital indicator. If it is between ± 0.2 mV/V, then the sensor is working properly.

NOTE: Make sure your sensors are working properly before moving onto the load cell installation procedure.

To stay on the cautious side, inspect the cable visually for any cuts or damaged sheath. Add a meter extra length for cable jointing before cutting the cable. It is important to ascertain the correct length of the cable and the cable jointing should be avoided as much as possible.

CAUTION: While removing the cable, use a spool and do the task by rotating the spool. This eliminates the chances of bending, twisting, or nicking of the cable.

The next step is to connect a required length of cable to the sensor. Follow the same procedure as described above to check the working of the sensor.

NOTE: Remember to make the adjustment in cable resistance when checking resistance between leads after cable jointing.
Eg: For EC-0107 cable (7 x 0.25 conductor) resistance is around 49 Ohm/km (multiply by 2 for both leads). Similarly, make the essential change in the resistance in case of any other cable.

Before mounting the load cell, it is important to note that the load cell assembly is always mounted on a machined seating pad which has a thickness greater than the flat bearing plate.

The seating pad is filled in with grout perpendicular to the axis of anchor, keeping the top surface the ground.

In the case of Centre Hole Load Cell, it should be installed between load distribution plates & flat …[Continue Reading]