AR4000 User’s Manual
14
LLL004001 – Rev 2.7
If the power supply falls below 5 volts for more than 100 microceconds, the
sensor will be reset to avoid unreliable operation that could damage it. If this
occurs, the quality of the power supply and its ability to provide a constant
voltage when there is noise on the AC line. If the power supply output voltage
can be increased to 5.5 volts, this may provide enough margin to prevent resets,
unless the supply has very poor line regulation.
7.3.1 Serial Communications Check
If no information is received over the serial port, check the power supply and
serial cable connection. The sensor may in a configuration that prevents serial
communication, such as being set at the wrong baud rate. Turn the power off,
press the button on the back panel of the 4000, and turn the power on with the
button held down. The LED should stay off until the button is released, and then
flash briefly (after a 5 second pause on the 4000-LIR). This will reset the sensor
to the factory default configuration (9600 baud, 8 bits, no parity, 1 stop bit), and
should enable serial communication with the host system.
If no serial data is being received and the LED is blinking several times a second,
the power supply voltage is low. It should be at least 5.0 volts at the end of the 6
foot sensor cable.
7.3.2 Range Output Check
If the range output is in error, check that the sensor and target are stationary and
stable, that the target is about 8 feet from the sensor as an initial test range, and
that the beam is hitting the target. The sensor may need to warm up before
reaching full accuracy: leave it on for a few minutes and re-check the range
accuracy.
One way to check the basic ranging operation of a sensor configured with pulse
width output is with an oscilloscope. Check the waveform on the pulse width
output. It should be a square wave swinging from 0.4 to 0.9 volts, with at rise/fall
time of about 20 nanoseconds. The duration of the low portion of this signal
should increase as the distance to the target surface increases. The signal repeats
approximately 200 times per second at low sample rate settings, depending on
the maximum range configured. For high sample rate settings, the signal will
repeat once per sample interval.
7.3.3 Analog Output Check
The analog signal outputs can be tested with a voltmeter or oscilloscope. Each
should be between 0 and 5 volts. Amplitude should change as the target is
moved, or as the target color changed. The ambient light output will also change,
to a lesser degree. Pointing the sensor at a brightly lit surface should raise the
ambient light output. Temperature should rise gradually for the first 15 minutes
or so from a cold start, or more rapidly if the heater power is applied.