Remote-processing RPC-2350 Manuel d'utilisateur télécharger pdf (Page 45)

CHAPTER 8 ANALOG I/O

8-3

The input range is -2.5V to + 2.5V. The result from an

AIN function is 0 for -2.500V, 2048 for 0. 000V, and

4095 for + 2.4998V.

4. Differential, ±2.5V input

CONFIG AIN chan,0,0

The input r anges from -2. 5V to + 2.5V. The r esult is

the difference of the two voltages. AIN will return 0

for a difference of -2.500V, 2048 for a difference of

0.000V, and 4095 for a difference of 2.498V.

ACQUIRING ANALOG DATA

Once the analog input is initialize d, the AIN function is

used to acquire data. The syntax is:

S = AIN(ch)

Where: ch = channel number, 0-7

This command reads the voltage and returns a number

from 0 to 4095 to the variable S. The number returned

corresponds to the voltage input and the type the channel

was configured for.

To convert the returned numbers to a voltage, use the

following formulas:

5V Unipolar: A = 0.0 0122 * AIN(chan nel)

±2.5 Bipolar: A = 0.00244 * AIN (channel) - 5

The AIN function requir es about 500 m icro-Seconds to

convert a channel of data. Additional time is needed to

store the data. Saving data to a single dimension array

takes 500 micro-seconds longer than saving to a sim ple

variable.

Data logging on a timer tick

Some application require that data be taken at fixed

intervals. The ON TIC K construct can be used to take

data in intervals from 0.01 to 655.35 seconds. The

program below takes 100 samples on 2 channels every

10 seconds.

10 DIM F(100,2)

20 ON TICK 10 GOSUB 50

30 ..this is a dummy loop

40 GOTO 30

50 F(I,0) = AIN(0)

60 F(I,1) = AIN(1)

70 INC I

80 IF I = 100 THEN ON TICK 10 GOSUB

90 RETURN

Line 80 shuts off interrupts after 100 samples.

MEASURING HIGHER VOLTAGES

Input voltages higher than 5V are measured by placing a

resistor in series with the input. Use the following

formula to determine the required series resistance:

Rs = Vi * 20,000 - 100, 000 0-5V range

Rs = Vi * 40,000 - 100, 000 0-2.5V range

Rs is the resistor value in ohms in ser ies with the input.

Vi is the maximum input voltage. If the result of your

calculation is 0 or negative, a series resistor is not

necessary.

NOTE: When an input voltage exceeds its voltage

range, other channels values are affected.

The 100K ohm resistor is R15. This is a 2% part. Y ou

may want to add a trim resistor in series with a fixed to

obtain higher accuracy.

Since input impedance is higher , noise incr eases. A

capacitor at the appropriate channel at W13 will reduce

noise.

CONVERTING ANALOG

MEASUREMENTS TO REAL WORLD

UNITS

Inputs are 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).

var result is in real world units (PSI, pounds, inches,

volts, etc.)

Example 1: To measure the results of an A/D

conversion in volts and the voltage range is 0 to 5V,

1 2 ... 40 41 42 43 44 45 46 47 48 49 50 ... 82 83

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Remote-processing RPC-2350 Manuel d'utilisateur Page 45

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