How do you measure Bubble Diameter in Blown Film Extrusion for bubble up ratio?

In blown film extrusion, the bubble diameter is typically measured using a caliper or other measuring device at the bubble's widest point, which is usually above the die. The bubble up ratio is calculated by comparing the measured bubble diameter to the die diameter. This ratio helps assess the efficiency of the extrusion process, as an optimal bubble up ratio contributes to uniform film thickness and quality. Accurate measurement is crucial for ensuring consistent film properties.