Models TA280-016, TA280-020, TA280-017 and TA280-021 can be mounted with 4 No. 6-32 machine screws from the rear. Models having a square adapter plate, such as Shockmasters® TA280-018, TA280-022, TA280-019 and TA280-023, can be mounted from the top with 4 No. 6 wood screws or machine screws. The Shock Indicator may be mounted on the container or on the packaged item. If it is mounted on the container, it will indicate the handling which the package as a whole has experienced. This way of mounting essentially checks on the handling methods. If the Shock Indicator is mounted on the packaged item, then the recorded shocks will be less severe due to damping by the packaging materials, such as isolators, foam cushioning, corrugated cardboard, etc. This type of mounting will indicate the amount of shock to which the packaged product was subjected.
Models TA280-016, TA280-017, TA280-018 and TA280-019 are sensitive to all acceleration forces except those coming from the top (i.e. passing through the hemisphere occupied by the plastic dome). Two equal-G Shockmasters mounted back-to-back will cover shocks from all possible directions. For long containers, it will be advantageous to have a Shock Indicator at each end of the package. Models TA280-020, TA280-021, TA280-022 and TA280-023 have longitudinal response and will only trip if subjected to axial shocks applied to the bottom of the Shockmasters. Side or transverse shocks have no effect.
When mounting a Shockmaster, it is important to consider the direction of the anticipated shock. For example, a Shockmaster with the plastic dome up will trip when banged on a table. In this case, the shock has come from the bottom of the Shock Indicator. This impact reflects what would occur if a box were dropped. On the other hand, if a Shockmaster is installed dome up in a vehicle which collides with an obstacle, the shock would come from the side of the Shock Indicator.
The Shockmaster consists of a spring-loaded weight with an integral trigger which engages with a spring-loaded sleeve. When tripped, this sleeve moves along a guide rod and exposes a red band on this rod. The upper periphery of the weight rests against a shoulder. The whole assembly is enclosed in a metal housing and transparent dome.
If the shock is applied to the unit along the long axis, the weight will be forced down against the spring. If the shock is applied from any side direction, the weight tips against the spring. Either movement disengages the trigger from the sleeve, which then moves under the action of its spring, exposing the red band. The Shock Indicator is now tripped. It can be reset by inserting a wire, such as a straightened paper clip, into the hole on the side of the dome and pushing the sleeve back to its cocked position. For models of 25 G and over, a plunger in the dome is depressed while the sleeve is pushed back.
In most cases, it is advisable to seal the resetting holes after resetting. This may be done by inserting 2 No. 4-40 screws with drilled heads into the two holes in the dome, safety wiring them and sealing the wire with an inspector's seal. Shockmasters with ratings of 25 G's or more are made tamper-proof by re-inserting one screw, threading safety wire through the holes in the plunger and screw head and securing with an inspector's seal.
AGM's guarantee of proper functioning of the Shockmaster under environmental conditions of dust, sand, moisture, etc., is dependent upon the proper sealing of the resetting holes. CAUTION: The transparent dome is easily damaged by solvents and thread locking solutions. RTV has been found to be suitable for sealing screw heads against dust and moisture intrusion.
INDICATOR WITH ELECTRICAL CONTACTS
Models TA280-019, TA280-021 and TA280-023 with electrical contacts can be used to check the Shockmaster® condition inside a package without opening it. If this type of Shock Indicator is enclosed inside a box or attached to the packaged item, wires can be run to the outside of the box and terminated there, either in pigtails or in suitable connectors. Do not solder to these connectors as this will damage the shelter. These wires must be crimped to the terminals on top of the dome. Polarity is immaterial. The condition of the Shock Indicator can then be determined from the outside by a simple continuity check with a portable ohmmeter, for instance, or with a dry cell and a light bulb. The contacts will be closed when the Shockmaster is tripped.
If the Shockmasters have to be tested for conformance with performance specifications published here or elsewhere, the tests must be carried out in accordance with AGM's test specifications. These specifications will be made available upon request.
The nominal rating is defined as the acceleration along the longitudinal axis (expressed in G's) necessary to trip the Shock Indicator mounted with axis vertical in gravity free space when applied for infinite time.
The response of the unit to a shock will vary with (A) the duration of the shock or (B) the effects of gravity and shocks coming from directions at an angle other than the Shockmaster's longitudinal axis or transverse plane.
(A) If the duration of the shock is short, say below 30 milliseconds, an acceleration in excess of the nominal rating will be needed to trip the unit. The following graphs approximate the "excess G's" required as a function of the shock duration for the most common G-ratings. These graphs are based on a "theoretical square wave" type shock. The "excess G's" have to be added to the nominal rating to obtain the response to short duration shocks. See Graph 1 for an example.
(B) Due to the effect of gravity, the attitude of the unit to the vertical varies the magnitude of tripping acceleration required. The relation of the direction of the applied acceleration to the vertical and the unit axis, also varies the magnitude of the tripping acceleration. See Case 1, Case 2 and Case 3 for examples.