ANALOG INPUT
SECTION 10
Page 10-1 RPC -320
Figure 10-1 Analog I/O
DESCRIPTION
The RP C-320 has 8 single ended analog input channels.
These channels are used to measure voltages from
transducers, 4-20ma current loops, thermistors, etc.
Input voltage r ange is 0 to 5 volts or ±2.5V with 12 bit
(4096 count) resolution. Signals are 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 ma y be used to
measure ambient temperature.
Two am plifiers are available to signal condition inputs.
By installing appr opriate r esistors and capacitor s, inp uts
are buffered, amplified, and filtered.
This chapter begins with basic information on connecting
and using ana log inputs. Later , de scriptions of how to
measure voltages other than 2.5 or 5 volts, temperature
measurem ent, data logging, using the amplifiers, and
calibration are presented.
CONNECTING ANALOG INPUTS
All analog inputs interface through connector P4.
Additional compone nts, such as r esistors and capacitors,
may be conne cted directly to the screw terminals.
For gr eatest accuracy, connect unused inputs to ground.
R17 is adjusted to trim accuracy to your system. See
Calibration
later in this chapter for more information.
Tem peratur e output or other signa l input may g o directly
to channel 0 via header H1. See
Temperature
Measurement
and
Amplifiers
below.
Overvoltage conditions
Inputs are protected over voltage protected. M aximum
voltage on 1 channel is 25 volts. M aximum voltage for
2 to 4 channels is 12 volts. Total input current m ay not
exceed 16 ma on all channels. Each channels input
current is computed by the following formula:
I
in
= (V
in
- 5)/4700
When V
in
< 5 volts, no curr ent flows into the channel.
NOTE:
An over-voltage condition on one channel
usually affects 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 a nalog input ter minal str ip). W hen both
analog and digital grounds come from the same device,
you will have to play aro und with the g rounds to
determine which scheme provides the best performance
f o r y o ur s ys te m .
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:
C O N F I G A IN
channel,mode, range
channel
ranges from 0 to 7 for single-ended inputs.
Differential inputs use adjace nt channels.
mode
defines single-ended or differential. 0 =
differential, 1 = single-ended.
Differential inputs operate in a special way. The
polarity of the input signal must be connected as shown
for an even or odd
channel.
For exam ple, when
channel
is odd (1, 3, 5, or 7), channel 0 m ust be more negative
than channel 1 otherwise a 0 is returned. Should the
relative polarity change, configure the even channel for
differential input and perform an AIN on it. Use the