CALIBRATION MADE EASY

CALIBRATION
A belt scale should be thought of as a precision instrument and its performance should be quickly and easily checked. Thayer Scale can provide an accurate reliable calibration using a calibrating weight instead of test chains for all scale capacities. Thayer Scale developed and patented the first automatic calibration system in 1971.

Thayer belt scales use a certified test weight in the form of a round bar which resides in one of two positions (“V” notches) on an intermediate lever between the approach-retreat suspension and the load cell itself. This bar provides tare counterbalance in its “zero” position, and simulated calibration loading in its “span” position. This method of “test weight” application is referred to as the “moveable-poise” method, in contrast to the additive weight method.

For belt scale calibration, the test weight represents a specific pounds per ft. loading value and the system instrumentation provides an automatic belt length measurement system. This combination produces accurate, repeatable calibrations free from human error. Unlike electronic calibration which simply simulates a load cell output to the instrumentation, the test weight mechanically exercises the scale mechanism. Thayer’s unique suspension design assures that the test weight will accurately load the scale, with one weight at less than 60 lb. while representing 80-100% of full scale load. Because the need for test chains is eliminated, calibration time is reduced to a matter of minutes and can be performed by one person.

THAYER TEST WEIGHT USING “SEE-SAW” SECONDARY LEVER
(Used where belt loading exceeds 300 lb. per idler)
CALIBRATION for 2RF-6A, 3RF-6A, 3RF-8A, 4RF-6AR, 6RF-8AR, NAR-6
On high capacity scales where it is impractical to apply the test weight directly to the end of the weighbridge because of the physical size of the test weight, a special arrangement of the secondary lever is used.

In this configuration, the test weight provides tare mass counter-balance in its “storage” position on the secondary lever and a test load of known value in its “calibrate” position. By taking advantage of ratios in the secondary lever, smaller, easily manageable test weight(s) can be used to produce significantly higher loading values. This method of applying the test weight does not introduce error on inclined conveyors. Since the test weight is on the scale at all times, its moments due to the sine component remains constant regardless of the test weight’s position on the lever.

The weight is always present on the secondary lever, which also serves as a means to counterbalance dead loads and control the force range presented to the load cell. In the movable poise weight design the weight resides in either one of two locating “V” notches, but is never added or subtracted from the lever itself.

In one position, the weight serves as “counterbalancing” weight for a portion of the dead load. In the other position, the weight serves as the calibration test load. This unique method, whereby the movement of the weight alone affords the means to apply a large effective test load, is the only practical and economical system known for calibrating “heavily loaded” conveyor scales.