Lysimeter Balance Design

The lysimeter balance uses mechanical advantage to increase measurement precision. This in combination with a counter-balance weight, allows a 25-pound capacity load cell to measure a soil tank weighing many time heavier than the load-cell capacity.

The single beam balance is designed to support a soil tank 12-inches (30-cm) diameter by 36-inches (90-cm) deep with a theoretical weight of 275 pounds (125 kg). The beam is designed to offer a 4-times mechanical advantage, which cuts the load cell weight down to 68 pounds (31 kg); nearly three times greater than the load cell capacity. By adding a counter-balance weight, it is possible to reduce the dry tare weight to only a few pounds; allowing the load cell to measure the change in water weight (approximately 18 pounds (8 kg) for a sandy soil with a dry bulk density of 1.45 g/cm3).

The double beam balance is designed designed to support a soil tank 18-inches diameter (45-cm) by 18-inches (45-cm) deep with a saturated soil theoretical weight of 337 pounds (153 kg). Force from left and right level 1 beams are transmitted to the level 2 beam via two connection rods. The connecting rod placement can be adjusted into 6 different positions, giving a mechanical advantage range from 20 to 45 times. There are trade-offs for this adjustability; higher mechanical advantage yields greater signal noise with a lighter counter weight, while lower mechanical advantage has lower noise with a much heavier counter weight. Although the rod position can be changed in the field, the rods must be positioned prior to installing the lysimeter outer shell and preferably prior to filling the soil tank.