USA57 Revision
1.2
95
Appendix F
Analog Inputs and Analog Feedback
Analog Inputs
The four inputs of the Accuriss are all ADC inputs.
The ADC values can be read via RS485, E.g.,
/1?aa<CR>
. These values are on a scale
of 0-16368 as the input varies from 0-3.3V. The inputs as shipped are good to about 7
bits resolution, but can be made to be better than 10 bits with the removal of the input
overvoltage protection circuitry (call factory for details).
The threshold upon which a digital “one” or “zero” is called can be varied with the “
at
”
command and affect the Halt H command or Skip S command.
Example:
Enter
/1at309999R<CR>
. This sets the threshold on input 3 to 09999. Note that it is
necessary to insert leading zeros after the input number (3), since the threshold value
must always be entered as five digits (00000-16368).
The thresholds for all four inputs can be read back with the
/1?at<CR>
command. The
Accuriss has a default threshold value of 6144 (1.24V).
It is possible, for example, to regulate pressure by turning a pump on or off depending
on an analog value read back, by designating the threshold of the One/Zero call as the
regulation point. E.g.
/1at308000gS03P1000G0R
.
A potentiometer can be wired to the Accuriss and its position read back via the
/1?aa<CR>
command. Note that the supply provided (which normally drives an LED) has 200 ohms in
series with 5V, so the use of a 500-ohm potentiometer will give a range of almost 0-3.3V range
on the inputs.
Potentiometer Position Command
Potentiometer 2 can be used to command the position of the motor. The value read back on
potentiometer 2, from 0-16368, is multiplied by the multiplier “
am
” and then divided by 256.
Then an offset given by “
ao
” is added. The motor will use this number just as if it had been
commanded by a
/1A12345R-
type command. Further, there is a “deadband” command, “
ad
”,
which sets a dead band on the 0-16368 potentiometer value read back such that a value
outside this deadband must be seen before a command is issued to cause a move.