Chapter 1. INTRODUCTION
1 - 2
1.2 Glossary
1.2.1 A - Analog Value
The continuous changeable value such as voltage, current, temperature, velocity, pressure and flow is
called analog value. For example, temperature changes continuously with time as shown in Fig. 1.1. The
PLC can process that continuous changeable temperature by use of the RTD input module.
1.2.2
D - Digital Value
In Fig.1.2, the number of man can be counted as 0, 1, 2, 3. The non-continuous changeable value as such
is called a digital value. On and Off signals can be denoted as a digital value 0 and 1, respectively.
Analog value cannot be directly input to the CPU
module for digital processing. Therefore, analog value
should be converted into a digital value to be input to
the CPU module. In addition, for external output of
analog value, digital value of the CPU module should
be converted into analog value.
1.2.3 Pt
This is a sensor that detects temperature as the type of resistance.
The Pt 100 outputs the resistance value of 100.00
Ω
for the temperature of 0
°
C
1.2.4 Burn-out Function
If a part of the connected RTD or cable is disconnected, the out-of-range voltage is input by the internal
burn-out circuit and the connection or disconnection is detected.
A/D
Conversion
CPU
(Digital
processing
)
D/A
Conversion
Analog
-200~-600
℃
Analog
0~
±
10V or
4~20mA
[Fig 1.3] Processing in the PLC
0
Temperature
time
time
Number of man
[Fig 1.1] Analog Value
[Fig 1.2] Digital Value
0