Remote-processing RPC-2300 Manuel d'utilisateur télécharger pdf (Page 26)

ANALOG I/O CHAPTER 8

Page 24 RPC-2300

Converting analog measureme nts

Inputs can be converted to engineering units of

measurement by performing scaling calculations in the

program. The AIN function returns values from 0 to

4095. To change these numbers into something more

meaningful, use the following formula:

var = K * AIN(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).

Example 1: To measure the results 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: You want to measure a 0 to 200 PSI

pressure transducer with 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. Adjust trim pot R7 for 5.000VDC.

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 write to this chip are a part of

CAM BASIC II and are not available for distribution.

There are no external assembly language accesses (calls

or jumps) available.

ANALOG OUTPUT

Two optional analog output channels can be

independently configured for three voltage ranges.

These ranges are jumpered in hardware. Refer to the

following table for jumper 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 always set [1-2] and [5-6]. Channel 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. The syntax is:

AOT channel, value

Where:

channel specifies the analog channel to write data 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 Formula

0 - 5 value= V * 819

1 2 ... 21 22 23 24 25 26 27 28 29 30 31 ... 35 36

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Remote-processing RPC-2300 Manuel d'utilisateur Page 26

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