Technical Information & Specifications

ShockWatch Label Placement

The correct placement of a ShockWatch label is paramount to achieve proper device operation. A ShockWatch label placed in the wrong position on a package can alter that device’s response characteristics and cause erratic results.

Whenever possible, the ShockWatch label should be placed on as rigid an area as possible. The reason for this is that if the surface to which the label is affixed is flexible, or can flex, it will dissipate an indeterminate amount of shock. The selection guide for ShockWatch devices is based on the assumption that the label is placed on a package at a position that has minimal flex. If a ShockWatch label is placed in a non-rigid position, its activation response will not correlate with the selection guide.

Typically, the most rigid area of a container (box) is at or near a corner. The most flexible area of a container is the center of a side. To prove this to yourself, press against the center of one side of a corrugated container. You will see that it easily gives way and flexes. Now, press against that same side but at a point near the junction of that side with one of the other sides (corner). You will see that there is considerably less flex.

In conclusion, if a ShockWatch customer reports erratic results in using the ShockWatch labels, the first item to check is the placement of the label.

Packaging

As you well know, the packaging of an item plays a very important role in ensuring that the product will reach its destination without damage. But do you know specifically how packaging protects the contents? The assumption is that packaging simply absorbs or dissipates shock. Actually, packaging uses physics to alter shock or impact so that it doesn’t render damage to the contents. Here is how.

Figure 3 shows a damage boundary curve (DBC). A DBC can be developed for every product made. A DBC shows what shock is required to damage a product. Any impact whose characteristics fall within the damage area of the DBC will damage that product. For instance, on the DBC shown, an impact of 50G @ 5 ms would damage the product because that impact is within the damage area. For the same DBC, an impact of 10G @ 5 ms would not damage the product because it is outside the damage area. Two interesting characteristics of a DBC are 1) it clearly shows that for all products, there is a minimum acceleration, and 2) a minimum time duration that must be exceeded in order to render damage to a product.

Figure 4 shows two shock pulses. The top pulse represents what a product is exposed to when it is dropped a specific height with no packaging. The bottom pulse represents what a product is exposed to when it is dropped from the same height but is protected by packaging. Each pulse occupies approximately the same area, as represented by the numbered squares. This area is called delta V, or rather, the change in velocity experienced by the product when it was dropped. v is purely a function of the drop height and since drops from the same height generated these shock pulses, they have the same v.

So how can two shock pulses have the same v, but be shaped so differently? When the product was dropped with packaging, the first thing to hit the ground was the box. When the box touched the ground, it came to a stop very quickly. The amount of time required for an object (box) to stop once it has impacted another object (ground) is what we call the time duration of an impact. Although the box had stopped, the contents continued to move by compressing the packaging foam. Thus the contents had a longer time duration. So if the box and contents were experiencing the same v, but the contents experience a longer time duration, the peak acceleration seen by the contents had to be lower.

Refer to the DBC on figure 3. You will see two points. One is marked “A1, T1″and the other is marked “A2, T2.” “A1, T1” represents the shock pulse without packaging shown on figure A. As you can see “A1, T1” is within the damage area of the DBC and thus would damage the product. “A2, T2” represents the shock pulse with packaging shown on figure 4. “A2, T2” is outside of the damage area and thus would not damage the product. So in effect, what the packaging did was to increase the time duration, lower the peak acceleration, and get the impact out of the damage area of the DBC.

So packaging really just changes the characteristics of shock to not damage the contents.