Page 48 - Programmable Logic Controllers, Fifth Edition

Analog input
modual
1
Temperature
probe 1C
Sensor 2
transducer Transmitter 2C
0 to 10 V
DC signal 3
3C
4
10 4C
Volts
DC
0
Time
Figure 2-24 Analog input module circuit.

Two-wire (ANL COM) points are electrically connected together
transmitter inside the module but not to earth ground. When wiring
Transmitter Input module single-ended analog input devices to the analog input
+
–
Power + IN+ card, the number of total wires necessary can be limited
supply – IN–
ANL COM by using the ANALOG COMMON terminal, as shown
Three-wire in Figure 2-26. Note that differential inputs are more
transmitter immune to noise than single-ended inputs.
Transmitter The analog output interface module receives from
supply signal Input module
Power + IN+ the processor digital data, which are converted into a
supply – GND IN– proportional voltage or current to control an analog field
ANL COM
Four-wire device. The transition of a digital signal to analog values
transmitter is accomplished by a digital-to-analog (D/A) converter,
Transmitter the main element of the analog output module. An analog
supply signal Input module
Power + + + IN+ output signal is a continuous and changing signal that is
supply – – – IN– varied under the control of the PLC program. Common
ANL COM devices controlled by a PLC analog output module in-
clude instruments, control valves, chart recorder, elec-
Figure 2-25 Wiring two-, three-, and four-wire sensors to tronic drives, and other types of control devices that
an analog input module. respond to analog signals. They employ standard analog
output ranges such as ±5 V, ±10 V, 0 to 5 V, 0 to 10 V,
Power + Transmitter 4 to 20 mA, or 0 to 20 mA.
+
supply – signal IN 0 + Figure 2-27 illustrates the use of analog I/O modules
IN 0 – in a typical PLC control system. In this application the
Transmitter ALL COM
+ signal IN 1 +
IN 1 –
Analog output
Transmitter ALL COM
+
signal IN 2 + Valve
IN 2 –
Transmitter ALL COM Level PLC
supply signal sensor
+ + IN 3 +
Ground
IN 3 –
ALL COM Analog input

Figure 2-26 Wiring single-ended analog input devices. Figure 2-27 Typical analog I/O control system.

PLC Hardware Components Chapter 2 29

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