The test is performed independently on a pair of test sites, with only one site being tested at a time. At each site, 50 products (detonators) are tested using a precisely defined procedure.
At high temperature, the firing current is set to the specified value (usually 240 mA) and the firing pulse length is set to 10s. The firing current is applied to the first product. If occurs ignition at at leas one detonator, the firing current is reduced by 5 mA in the second step and the same activity is performed. If the current did not lead to ignition, the firing current is increased by 5 mA in the next step. This procedure is repeated until the firing current is applied sequentially to all 50 products in one holder.
At low temperature, the firing current is set to the specified value (usually 660 mA) and the firing pulse length is set to 10s. The firing current is applied to the first product. If ignition occurs, the firing current is reduced by 10 mA in the second step and the next detonator is tested. If the current did not lead to ignition, the firing current is increased by 10 mA in the next step. This procedure is repeated until the firing current is applied sequentially to all 50 products in one holder.
The products are then subjected to a relatively complex evaluation, the result of which is shown in the figure:
The system consists of an industrial computer with usual components (keyboard, mouse, monitor, printer). The test device includes a pair of relay matrices controlled by digital outputs. Each of the 5 x 10 channel matrices allows firing current to be switched on for one of the 50 test products in the test matrix. A total of 20 bits is required for control. Device manufactured by Indet, which was modified for control by serial line RS232, is used for generation of firing pulses .
A pair of cheap vibration sensors are used, one for each test chamber, to register whether an explosion has occurred. The absolute value of the vibration is of no interest, but whether the vibration has exceeded a certain set threshold level is important. Exceeding this set level will flip the flip-flop circuit connected at the sensor output; the state of this flip-flop is sensed by the digital input of the computer.
The basis of the system is in a measuring program created in the TestPoint development environment. The program controls the entire measurement, guides the operator and controls the equipment.
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