Remote Technologies RPC-320 Connecting Analog Inputs, Initialization, Overvoltage conditions

ANALOG INPUT

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:

Iin = (Vin - 5)/4700

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

NOTE: An over-voltage condition on one channel

SECTION 10

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 for your system .

Figure 10-1 Analog I/O

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 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

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