AR4000 User’s Manual
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LLL004001 – Rev 2.7
Otherwise, the output will be the indicated sensor range, uncompensated for
temperature, signal strength, and other effects.
In the default configuration, the current output is updated 5 times per second.
This may be increased or reduced with the Set Sample Rate Command, using
either the pushbutton on the back of the sensor or the ‘S’ command over the
serial port.
Best accuracy and noise immunity is obtained by loading the line with a 500 ohm
resistor to ground at the measurement point. The default configuration is for
calibrated output, with the zero current set to 4 milliamps, the zero point at zero
distance, and the span at 650 inches.
The minimum current loop span is approximately 9 inches. Attempts to set a
smaller span will result in a span of about 9 inches.
The direction of increasing current output can be reversed by setting the span to a
value closer that the previously set zero point.
The current loop output is a single line: The return portion of the “loop” is
through ground.
11. Serial and Analog Output Performance
Specifications
11.1 Sample rate
Maximum of 770 samples per second for calibrated output, 3300 samples per
second for uncalibrated output. The sample rate is programmable to any rate
below this, down to one sample per 10 seconds, with a resolution of 1
microsecond. Valid arguments for the sample rate command are 20
(microseconds per sample) to 9999999 (microseconds per sample).
Sample rate has a slightly different meaning for serial output and for the optional
current loop output. For serial output, one sequence of characters is transmitted at
each sample interval. The sample rate may be limited by the time required to
obtain and calibrate a range measurement in calibrated output mode. It may also
be limited by the time required to transmit each sample at the specified baud rate.
If the baud rate is the limiting factor, data will be transmitted continuously. For
calibrated output, the maximum sample rate is 1400 microseconds per sample if
only the serial output is enabled.
For current loop output, the current transmitted is updated once per sample
interval up to the limits of the sensor’s sample rate capability. If a low sample
rate is specified the resolution of the output will be 1 part in 4000 over 0 to 20
milliamps, the limit of the output converter. If only the current loop output is
enabled, the maximum obtainable sample rate is 1300 microseconds per sample.