AR3000 User’s Manual
30
Rev 1/10
8.
External Trigger Operation
The AR3000 can operate with a hardware trigger that has been connected according to the diagram in
Section 4.1.5. To operate with an external hardware trigger, the AR3000 must operate in the Trigger
Measurement Mode, started by the Start Trigger command (DF).
The Trigger Delay (TD) settings affect the External Trigger operation.
8.1.
Start External Trigger Mode (DF) (<Esc> to stop)
This command causes the AR3000 to enter the External Trigger mode. The AR3000 will then
remain in the External Trigger mode until stopped with the Escape character (0x1B) via the serial
port (<Esc> key in HyperTerminal). While in the External Trigger mode the AR3000
continuously waits for external trigger events. On receipt of each trigger event, the AR3000 emits
a single laser pulse and acquires a single distance measurement. These measurements are counted
and stored until the count matches the Samples Averaged parameter value (SA), and then the
Sample Result is computed and the outputs are generated (serial, analog, and alarms). For
example, if SA is set to 20, then 20 triggers are required to get a single result (see section 7.2).
The ‘trigger event’ response to the external trigger input signal is specified with the Trigger
Delay parameters (TD – See section 8.2).
Type
DF<Enter>
to start the External Trigger mode. This command does not change any
configuration settings.
The serial port will respond with
external trigger on ...
Type
<Esc>
to stop waiting for an external trigger. Note: This is the only way to stop.
The serial port will respond with
external trigger off
.
The time to get a result depends on the number of samples averaged (SA) and the setting for
trigger delay (TD). The measurement frequency parameter (MF) is ignored in the External
Trigger mode. The time between the last bit of a trigger impulse and the first bit of output value
is approx. 200 µs. The trigger delay, measurement frequency and the average will influence the
time delay
8.2.
Trigger Delay (TDx y)
The Trigger Delay parameters specify the delay and transition edge used in the External Trigger
mode. The factory default setting is TD0.00 0
Type
TD<Enter>
to display the current trigger delay values.
Type
TD x y<Enter>
to set the new trigger delay values. A space must separate the values.
The serial port will respond by displaying the new values.
x
: The delay time has units of milliseconds (ms) with a resolution of approximately 0.01ms.
The allowed range for the delay is 0 to 300 ms.
y
: The transition edge has a value of 0 or 1.
0
falling edge – trigger input transition from HIGH to LOW
1
rising edge – trigger input transition from LOW to HIGH
Example:
TD8.5 0<Enter>
Sets the trigger event to happen 8.5ms after the trigger input signal
falls (external input goes from HIGH to LOW).
