Producing trigger signals, synchronized with a projectile’s arrival at location(s) downrange from the muzzle of a gun, is a frequent requirement for ballistic research experiments.  PAI’s model UDC-100 Up/Down Counter is ideal for providing such trigger signals at any user-selected location regardless of the actual projectile velocity.

As its name implies, an up/down counter counts and stores the time for a projectile to travel a known distance (i.e. the distance between two projectile detection stations), then immediately counts the stored time downward until zero is reached and a trigger signal is generated. If the up count and down count are performed at the same rate the trigger signal occurs when the projectile has arrived at a location downrange of the second detection station equal to the distance between the two detection stations regardless of the projecitle’s actual velocity.

The UDC-100 consists of four identical up/down counter circuits that are controlled by a pair of variable frequency counters (both of which are driven by a single quartz oscillator) that allow the frequency of the up count and down count to be set independently.  This feature allows the ratio between the up count and down count to be set such that a trigger signal can be generated when the projectile arrives at any location downrange of the second projectile detection station.

     Each of the four counter circuits can be set to provide trigger signals synchronized with the projectile’s arrival at the selected location or they can be preset with values to produce specific positive (post trigger) or negative (pre-trigger) time delays with respect to the primary down count. These time delays are useful for triggering instrumentation before projectile arrival and/or providing post arrival triggering.

In addition to operating in an up count followed by an immediate down count mode, the UDC-100 can be directed to hold the up count until a third input signal (from a third detection station) is received and the down count begins.  This mode proves useful if velocity detection stations are connected to a recoiling barrel and also for providing greater trigger accuracy at locations long distances from the projectile detection stations.

The UDC-100 uses a personal computer interface via a RS-232 connection.  Software for presetting and testing the unit and receiving its output is provided with the unit.  The unit produces two output signals from each of the four counter circuits, one TTL level signal and one 10-50V (settable) into 50 ohms impedance.

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