Remote-processing RPC-330 Manuel d'utilisateur télécharger pdf (Page 35)

ANALOG INPUT SECTION 10

Page 10-1 RPC-330

Figure 10-1 Analog I/O

DESCRIPTION

The RPC-330 has 8 single ended analog input channels.

These channels are used to measure voltages from

transducers, 4-20 ma current loops, thermistors, etc.

Input voltage r ange is 0 to 5 volts or ±2.5V with 12 bit

(4096 count) resolution. Signals may be single ended or

differential. Input impedance is 100K ohms to ground.

Reference IC U 14 has a voltage output that corresponds

to the IC tem peratur e. T his output may be used to

measure ambient temperature.

Two am plifiers are available to signal condition inputs.

By installing appropriate r esistors and capacitors, inputs

may be buffered, amplified, and filtered.

This section begins with basic information on connecting

and using analog inputs. Later, descriptions of how to

measure voltages other than 2.5 or 5 volts, temperature

measurement, data logging, using the amplifiers, and

calibration are presented.

CONNECTING ANALOG INPUTS

All analog inputs interface through connector P4.

Additional components, such as resistors and capacitors,

may be connected directly to the screw terminals.

For greatest accuracy, connect unused inputs to ground.

R17 may be adjusted to trim accuracy to your system.

See Calibration later in this section for more

information.

Temperatur e output or other signa l input may go directly

to channel 0 via header H1. See Temperature

Measurement and Amplifiers below.

Inputs are protected over voltage protected. M aximum

voltage on 1 channel is 25 volts. Maximum voltage for

2 to 4 channels is 12 volts. Total input current may not

exceed 16 ma on all channels. Each channels input

current is computed by the following formula:

= (V

- 5)/4700

When V

< 5 volts, no curr ent flows into the channel.

NOTE: An over-voltage condition on one channel may

affect readings on other channels.

Grounding

Analog ground is somewhat isolated from digital ground.

While the ground plane is connected between the two,

analog ground is a virtual "island" connected only in one

place to digital ground. To minimize noise pickup, the

sending device should be connected to analog ground

(located at the analog input terminal strip). W hen both

analog and digital grounds come from the same device,

you will have to play around with the grounds to

determine which scheme provides the best performance

for your system.

INITIALIZATION

Each channel is initialized for 0-5V, single ended input

upon power up. Inputs can be reconfigured for eight

single-ended, four differential, or a mixture of single-

ended and differential inputs. Input voltage ranges are 0

to 5V or ±2.5V for any single-ended channel or

differential pair. Syntax is:

CONFIG AIN channel,mode, range

channel ranges from 0 to 7 for single-ended inputs.

Differential inputs use adjacent channels.

Differential inputs operate in a special way. Use the

following tables for differential inputs.

When channel = odd

Pol. - + - + - + - +

CH # 0 1 2 3 4 5 6 7

channel 1 3 5 7

1 2 ... 30 31 32 33 34 35 36 37 38 39 40 ... 47 48

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Remote-processing RPC-330 Manuel d'utilisateur Page 35

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