Remote Processing RPC-2300 - Manual (Page 26)

ANALOG I/O CHAPTER 8
Page 24 RPC-2300
Converting analog measureme nts
Inputs can be converted to engineering units of
measurem ent by performing scaling calculations in the
progr am. The A IN func tion retur ns values fr om 0 to
4095. To change these numbers into something more
meaningful, use the following formula:
var = K * AI N (n)
n is the analog channel to read. K is the scaling
constant. K is obtained by dividing the highest number
in the range of units by the maximum AIN count (4095).
E x am p le 1 : T o m ea su r e t he r es ul ts of an A / D
conversion in volts and the voltage range is 0 to 5V,
divided 5 by 4095 to obtain K.
K = 5/4095
K = .001221
Your program could look something like:
1000 C = .001221 * AIN(N)
Example 2: Y ou want to measure a 0 to 200 PSI
pressure transducer w ith a 0 to + 5V output. Divide 200
by 4095 to obtain the constant K.
K = 200 / 4095
K = .0488
The code can then look like:
1000 B = .0488*AIN(0)
CALIBRATION
The A/D converter is calibrated using an external
voltmeter. For 12 bit accuracy, you must use a
voltmeter with an accuracy of 0.02% or better.
To calibrate the SBS-2300:
1. Connect the digital voltmeter ground to U10,
pin 11.
2. Connect the digital voltmeter '+ ' lead to U10,
pin 14.
3. A d ju s t t r im p o t R 7 fo r 5 . 00 0 V D C .
You may increase the reference voltage to a higher
value, up to 5.12V. This will allow you to detect if an
input device is at or above its output range (5V).
ASSEMBLY LANGUAGE ACCESS
The A/D converter is serially accessed. The routines
used to initialize, read and w rite to this chip are a part of
CAM BASIC II and are not available for distribution.
Ther e are no externa l assembly la nguage ac cesses (calls
or jumps) available.
ANALOG OUTPUT
Two optional analog output channels can be
independently configure d for three vo ltage ranges.
These ranges are jum pered in hardwar e. Refer to the
following table for jum per settings.
Range J7-17 J7-19
(AOT 0) (AOT 1)
0 - + 5 W2[2-4] W2[1-3]
0 - + 10 W2[8-10] W2[7-9]
±5V W2[6-8] W2[5-7]
W3 is alw ays set [1-2] an d [5-6]. Channe l 0 output is
pin 17 and channel 1 is pin 19.
Programming voltage output
The AOT command is used to send data to an analog
output. T he syntax is:
AOT channel, value
Where:
channel specifies the an alog channe l to write da ta to
and can be either 0 or 1. channel 0 is on pin 17 and
1 is on pin 19.
value is the value to output from 0 to 4095.
Use the following table to convert from a desired voltage
to a value.
Range For mula
0 - 5 value= V * 819